literature review on ro water purifier

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A Review on Reverse Osmosis and Nanofiltration Membranes for Water Purification

1 Department of Materials Science and Engineering, The Ohio State University, 2041 N. College Road, Columbus, OH 43210, USA

Zhiyuan Feng

2 State Key Laboratory of Precision Measurement Technology and Instrument, Tianjin University, Tianjin 300072, China

3 Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, China

Zhien Zhang

4 William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH 43210, USA

Sustainable and affordable supply of clean, safe, and adequate water is one of the most challenging issues facing the world. Membrane separation technology is one of the most cost-effective and widely applied technologies for water purification. Polymeric membranes such as cellulose-based (CA) membranes and thin-film composite (TFC) membranes have dominated the industry since 1980. Although further development of polymeric membranes for better performance is laborious, the research findings and sustained progress in inorganic membrane development have grown fast and solve some remaining problems. In addition to conventional ceramic metal oxide membranes, membranes prepared by graphene oxide (GO), carbon nanotubes (CNTs), and mixed matrix materials (MMMs) have attracted enormous attention due to their desirable properties such as tunable pore structure, excellent chemical, mechanical, and thermal tolerance, good salt rejection and/or high water permeability. This review provides insight into synthesis approaches and structural properties of recent reverse osmosis (RO) and nanofiltration (NF) membranes which are used to retain dissolved species such as heavy metals, electrolytes, and inorganic salts in various aqueous solutions. A specific focus has been placed on introducing and comparing water purification performance of different classes of polymeric and ceramic membranes in related water treatment industries. Furthermore, the development challenges and research opportunities of organic and inorganic membranes are discussed and the further perspectives are analyzed.

1. Introduction

Human welfare has been promoted by continued economic growth, which is accounted for by mechanization and industrialization. However, increasing income and wealth would cause ecological problems, since natural resources are used as inputs of several products, and the pollution of the environment is directly linked to the production scale [ 1 , 2 ]. Water shortage is one of the problems caused by global industrialization. In developing countries, untreated wastewater entered rivers and seas, leading to ground water contamination and limited clean water supply. In order to protect the environment and save mankind, various actions have been taken to tackle industrial pollutants [ 3 , 4 , 5 , 6 , 7 ]. On the other hand, continued population expansion and urbanization also lead to increasing residential water demand. The United Nations predicts that with the current population growth rate, in ten years half of the geographic regions of the world will be impacted by water scarcity [ 8 ]. Water purification and desalination have been used more and more around the world to provide people with fresh and clean water, especially in water-stressed countries such as Qatar, the United Arab Emirates, and Israel. These regions need inventive and viable approaches for safe water supply to support population growth. Since 1980, filtration systems equipped with nanoporous membranes have been commercialized and membrane separation has become a rapidly emerging technology in many industrial applications such as food industry, petroleum industry, chemical processing industry, pulp and paper industry, pharmaceuticals and electronic industry [ 9 , 10 , 11 , 12 , 13 , 14 ]. In these industries, wastewater purification is an essential process that involves membrane separation technique. According to particle size of retained species, water purification systems such as reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF) and microfiltration (MF) have been introduced globally [ 15 , 16 , 17 , 18 ]. A description of membrane types with corresponding pore diameter and retained species is shown in Figure 1 . Meanwhile, significant progress has been made in research on RO membranes made from different materials for desalination applications [ 19 ].

Classification of membranes for water purification in terms of pore size and retained species.

It is well known that polymeric membranes are currently used the most in seawater desalination and wastewater treatment industries due to their well-developed and outstanding performance [ 20 , 21 , 22 ]. Research is still being conducted to solve problems related to performance limitations and post-treatment process. Fouling is one of the main drawbacks of polymeric membranes. Surface structure and materials have been modified to suppress fouling effect. Introduction of materials that contain inorganic fillers in organic matrix such as mixed matrix membranes (MMMs) is a significant achievement for underlying issues. In addition to slow improvement achieved in polymeric membranes, inorganic membranes have gained growing interest due to their long-term chemical and thermal stabilities and high mechanical strength [ 23 ]. In general, inorganic membranes include metal oxide membranes and carbon-based membranes ( Figure 2 ). Alumina, zirconia, titania and their mixtures are the most commercialized metal oxide membranes in the market. Almost all inorganic membranes share a common structure, containing a macro-porous support and a meso- or micro-porous barrier layer. In the industry, ceramic membranes are usually used in systems whose operating conditions are challenging to polymeric membranes (high temperature, corrosive effluent, etc.). However, recent studies on cost-effective preparation method using cheap materials indicate a commercialization potential for ceramic membranes [ 24 , 25 ]. In addition, ceramic membranes synthesized from advanced porous materials such as carbon nanotubes (CNTs) and graphene oxide (GO) have been identified as the most promising inorganic membranes in thin film technology [ 26 , 27 ]. These membranes have excellent permeability and selectivity, and their structures offer high productivity and practically efficient performance in desalination and water purification processes.

Representative reverse osmosis (RO) and nanofiltration (NF) membranes for water treatment.

This paper critically reviews the growth and achievement in organic and inorganic membrane studies for RO and NF procedures. The review will start by introducing the synthesis method and structural properties of recent RO and NF membranes, followed by discussing and comparing water purification performance of representative RO and NF membranes made from organic and inorganic materials. The wide scope of this review highlights the potential of RO and NF membranes made from new materials for further research and improvement. Finally, challenges and remaining issues that need to be addressed for further work are summarized.

2. Reverse Osmosis and Nanofiltration Membranes

2.1. polymeric membranes.

Polymeric/organic RO and NF membranes have dominated the global market since 1980 due to their excellent performance and low cost. Some state-of-the-art polymeric RO and NF membranes are listed in Table 1 together with manufacturer, selective layer composition, operation condition, and purification performance. It can be seen that current market is dominated by thin-film composite (TFC) membranes due to their outstanding performance. Important polymers that are being used for making RO and NF membranes are polyamides, cellulose acetate, cellulose diacetate, cellulose triacetate, piperazine, etc. Polyamide is a macromolecule containing recurring amide (-CO-NH-) groups, and can be found both naturally and artificially. Examples of natural polyamide are wool, silk, and angora. Cellulose-based polymers are usually prepared by phase inversion method, as introduced in Section 2.1.1 . In this section, two classes of organic membranes made from different polymeric materials are reviewed.

Commercial polymeric RO and NF membranes for water purification.

2.1.1. Cellulose-Based Membranes

Cellulose-base (CA) membranes have been developed and commercialized for more than 60 years. In 1955, cellulose acetate membranes were prepared and introduced by Reid et al. using acetone as the solvent [ 28 ]. The general synthesis process of CA membrane is called phase inversion method: cellulose triacetate is first dissolved in an organic solvent or solvent mixture to form a casting solution. Then the solution is coated on a flat or tubular support. Finally, the support is immersed in a non-solvent bath, where polymer coagulation occurs and a CA membrane forms. Although CA membranes made by Reid at al. had good selectivity, the water permeability was extremely low and could not be used for practical applications. In 1963, Loeb et al. invented the first efficient RO membrane: cellulose diacetate (CDA) membrane. CDA membranes had much higher flux compared to CA membranes but were prone to biological attack [ 29 ]. The invention of CDA membranes accelerated the development of cellulose triacetate (CTA) membranes, which had slightly stronger thermal, chemical, and biological stabilities [ 30 ]. With asymmetric morphologies, cellulose-based membranes have anisotropic structures, consisting of an upper skin layer on a porous sublayer [ 31 ]. Both the skin layer and porous sublayer have identical chemical composition. The filtration performance of CA membranes depends on the degree of acetylation. For instance, CA membrane with 40 wt% acetate and a 2.7 degree of acetylation had a salt rejection between 98% and 99% [ 32 ]. Higher acetylation will result in higher selectivity but lower water permeability. CA membranes are stable in pH range 4–6. In acidic and basic feed solutions, hydrolysis reaction will happen and lower the selectivity.

Though membranes with better separation performances and comparable costs were fabricated, some studies were reported to improve CA membranes. Chou et at. found dispersing silver nanoparticles on CA membrane surface would increase its biological stability while maintain the permeability and salt rejection [ 33 ]. Coating phospholipid polymer on CA membrane during phase conversion resulted in a fouling-resistant membrane with high water flux [ 34 ]. A small percentage of mineral fillers such as aluminum oxide improved the compaction resistance of CA membranes remarkably [ 35 ]. During the past four decades, thin-film composite (TFC) membranes, whose permeability and rejections surpass those of CA membranes, have dominated the market. However, CA membrane still exists due to its overall exceptional chlorine resistance, which depends on several parameters such as polymer type, synthesis procedure, and pH of feed solution. Since feed water disinfection is a necessary step in RO and NF installations and chlorine is the most common choice of disinfectants, it is important to have chlorine-tolerant membranes for water treatment. Table 2 shows effects of various processing methods on chlorine resistance. Current research mainly focuses on modifications of TFC membranes for chlorine resistance improvement.

Effects of various processing methods on chlorine resistance.

2.1.2. Thin-Film Composite Membranes

TFC membranes were invented by Cadotte in the 1970s, but were not widely used until the second half of the 1980s [ 43 ]. Polyamide (PA) membranes were developed by Hoehn and Richter and had good water purification performance. The main drawback of PA membranes was susceptibility to free chlorine attack [ 44 ]. After development of TFC membranes, it was found the PA TFC membranes had outstanding separation performance as well as better chlorine resistance. As shown in Figure 3 , the structure of a PA TFC membrane consists of a thin selective barrier layer on a porous support [ 45 , 46 , 47 ]. The support has a microporous structure (UF membrane), providing mechanical strength and high water flux, and the barrier layer has a function of ion separation. Compared with CA membranes, which can only be made from linear, soluble polymers, TFC membranes have more desirable characteristics. Many materials (linear and crosslinked polymers) and approaches can be used to synthesize or modify the porous support and barrier layer individually to optimize the thermal and chemical stabilities, permeability, salt rejections, etc. Many papers focus on improving TFC membranes for RO applications have been published. On the other hand, the manufacturing cost of TFC membranes is higher than that of CA membranes since at least two membrane fabrication steps are needed: synthesis of microporous support followed by synthesis and deposition of barrier layer on microporous support.

Thin-film composite membrane structure.

The porous support plays an important role in providing mechanical strength to withstand high pressure during RO and NF processes. Meanwhile to form a defect-free barrier layer, the surface of the support needs to be uniform and smooth. Polysulfone is one of the most significant microporous supports for TFC membranes [ 48 ]. The surface pore size of polysulfone support ranges from 1.9 nm to 15 nm, with a surface porosity up to 16% [ 49 , 50 ]. The selectivity generally increases with decreasing pore size [ 51 ]. Since polysulfone shows good structural stability in a wide pH range, barrier layers made from highly acidic or alkaline precursors can be coated on polysulfone substrates. The disadvantages of polysulfone include poor weatherability, low chlorine resistance, and prone to stress cracks. Adding nanoparticles and applying new preparation methods are two main approaches to improve polysulfone supports. A chlorine-resistant TFC membrane can be made by metalation sulfochlorination of polysulfone [ 52 ]. Plasma treatment on polysulfone support results in the exhibition of hydrophobicity, which optimizes chlorine resistance and water permeability [ 53 , 54 ]. In addition to polysulfone, CA, polyimide, polypropylene, polyketone and polyethylene terephthalate (PET) have also been used as porous supports [ 55 , 56 , 57 , 58 ]. A hydrolyzed PA CA membrane has been fabricated and the covalent bond between porous CA support and selective PA barrier layer indicates a chemical stable structure. This membrane exhibits a NaCl rejection up to 97% [ 58 ]. In addition, TFC membranes synthesized by heat and plasma treatments using electrospun nanofibers as supports showed remarkable filtration performance [ 59 ]. Yoon et al. have prepared a PA TFC membrane using polyacrylonitrile (PAN) nanofibrous scaffold as porous support. The experimental result showed the PA PAN composite membrane has similar sulfate rejection rate (98%) but 38% higher water permeability compared to commercial NF membranes (NF270) [ 60 ]. Several recent studies focus on the effect of support pore size on barrier layer formation and water purification performance, but there have been no consistent conclusions so far [ 61 , 62 ].

Most selective barriers of TFC membranes are synthesized by interfacial polymerization, which occurs at an interface between two immiscible monomers/solvents [ 63 , 64 ]. Once a layer forms at the interface, solvents from both sides cannot pass through it and therefore the reaction stops, producing a membrane thinner than 200 nm ( Figure 4 ). Heat treatment is necessary since interfacial polymerization happens at elevated temperature. The purification performance of TFC membranes is primarily determined by barrier layer, which is affected by solvent type and concentration, curing condition and temperature. Table 3 summarizes precursors for preparing TFC membranes by interfacial polymerization method for water purification in recent studies. Due to their good mechanical property and outstanding rejection ratio, TFC membranes are used in a large number of purification tasks, especially in desalination. The main problem associated with TFC membranes is their flux and salt rejection decrease gradually as a result of fouling, particularly in treating with wastewater containing bacteria and nutrients. According to Mansourpanah et al., TFC membranes with antifouling property can be prepared by grafting functional groups or adding hydrophilic additives on membrane surface through radiation or plasma treatment [ 65 ]. The altered barrier layer becomes smooth, hydrophilic and has similar surface charge as foulants. Therefore the interaction between contaminants and membrane surface is reduced. It is also found that TFC membranes blended with polyacrylamide and polymethacrylic acid exhibit biofouling resistance [ 66 ]. Deposition of natural hydrophilic polymers such as sericin would increase surface hydrophilicity of TFC membranes, and improves selectivity and fouling resistance [ 67 ]. Another drawback of TFC membranes is poor chlorine resistance. During water purification process, chlorine (frequently used as disinfectant) changes the hydrogen bounding in TFC membranes, resulting in performance decay [ 68 ]. Thus, it is essential to increase chlorine resistance of TFC membranes. A chlorine-resistant TFC membrane has been invented by Yao et al. by secondary interfacial polymerization method to eliminate the interaction between unreacted amino groups and free chlorine [ 69 ]. Experimental results indicated TFC membranes blended with layered double hydroxides (LDHs) have high porosity and hydrophilicity, exhibiting superior chlorine resistance and anti-fouling capacity [ 70 ]. Similar studies focus on enhancing chlorine resistance of TFC membranes by incorporating additives are available in literature [ 71 , 72 , 73 ]. From a technique perspective, methods such as atomic layer deposition (ALD) controls membrane thickness precisely through sequential surface reactions [ 74 ]. Hydrophilic selective barriers synthesized using this technology have excellent fouling and chlorine resistance.

Mechanism of interfacial polymerization.

Monomers and performance evaluation for thin-film composite (TFC) membranes prepared by interfacial polymerization method.

2.2. Ceramic Membranes

Although ceramic/inorganic RO and NF membranes have only been studied for 30 years and are in early stage of commercialization, their encouraging performance, as exemplified in Table 4 , offers great potential for water purification. In this section, two classes of ceramic membranes made from different inorganic materials are discussed.

State-of-the-art inorganic RO and NF membranes for water purification.

2.2.1. Metal Oxide Membranes

Compared to polymeric membranes, inorganic membranes offer higher chemical stability and stronger mechanical properties. Metal oxides such as alumina, zirconia, and titania form an important class of ceramic membranes. Conventionally, a RO metal oxide membrane has an asymmetric structure consisting of a thick macroporous (>50 nm) support, an intermediate mesoporous (2–5 nm) layer, and a thin selective (<1 nm) top layer. A NF metal oxide membrane has similar structure as RO metal oxide membrane but contains no selective top layer [ 101 , 102 , 103 ]. The most widely used approach for preparing metal oxide ceramic membranes is sol-gel method, which converts precursor solutions into solid membranes in four steps: precipitation reaction first happens between hydrolyzed precursors, followed by a peptization reaction in which precipitation transforms into a colloid sol. The stable sol is then coated on a porous support and gelates during drying. Finally high temperature sintering is applied to the membrane to optimize mechanical properties and pore structure [ 8 , 89 ]. In order to make homogeneous membranes with less defects, colloidal particles are dispersed uniformly in the solvent by stabilizers such as nitric acid, ethanolamine (MEA) and triethylenetetramine (TETA) [ 104 , 105 , 106 ]. Since complex fabrication process of multi-layered membranes as well as expensive precursor materials indicating high manufacturing cost, simplified synthesis method and use of cheap materials will reduce the production cost and accelerate the development and commercialization of ceramic membranes.

One of the most widely studied inorganic membranes is alumina membrane, which has an average pore size of 2–5 nm (MWCO of 3000–1000 Da) and is commonly used in NF systems or as an intermediate layer in RO membranes [ 107 ]. Alumina membranes with pore size smaller than 1 nm has been made, but showed low permeability (5 LMH/bar) and cannot be used for industrial purposes [ 8 ]. Wang el al. have prepared a supported γ-Al 2 O 3 hollow fiber membrane with a mean pore size of 1.61 nm that demonstrates a high water permeability of 17.4 LMH/bar [ 85 ]. This membrane exhibits good selectivity for multivalent ions such as Ca 2+ (84.1%), Mg 2+ (85%), Al 3+ (90.9%) and Fe 3+ (97.1%), but very low retention of monovalent ions such as NH 4 + (27.3%) and Na + (30.7%). Recent studies focus on surface modification of alumina membrane to further improve its purification performance. For instance, a mixed matrix carbon molecular sieve (CMS) and α-Al 2 O 3 membrane fabricated by vacuum-assisted impregnation method has a water flux up to 25 kg m −2 h −1 and a salt rejection between 93% and 99% when tested using 3.5 wt% NaCl (seawater) at 75 °C [ 87 ]. Ren et al. changed the surface of a porous alumina membrane from hydrophilic to hydrophobic by fluoroalkylsilane (FAS) grafting, resulting in a water flux of 19.1 LMH and salt rejection over 99.5% [ 88 ]. Such outstanding salt retention and water permeability hold promise for practical desalination applications. In addition to surface modification, using cheap precursor materials provides both economic and environmental benefits. Researchers have used Al 2 O 3 hollow fiber supports and coal fly ash, a byproduct of coal burning, to synthesize Al 2 O 3 -NaA zeolite membranes successfully. The Al 2 O 3 -NaA zeolite membrane has been used to treat wastewater containing lead ions (Pb(Ⅱ), 50 mg L −1 ) and possesses a Pb(Ⅱ) removal rate of 99.9% [ 108 ].

Zirconia and titania are other popular materials for ceramic membranes. In sol-gel method, zirconium alkoxides are often used as precursors to prepare zirconia sols [ 109 , 110 ]. However, some zirconium alkoxides such as zirconium propoxide is water-reactive, which could produce agglomerates rather than stable nanoparticles. Therefore at the beginning few laboratories had successfully synthesized zirconia membranes. In 1998, Garem et al. discovered that adding 13 mol% magnesium would enhance the chemical and thermal stabilities of zirconia sols [ 111 ]. Since then many stabilizers have been investigated for preparing zirconia membranes. Glycerol has been introduced into the sol-gel process to make ZrO 2 NF membranes for treating high-salinity wastewater. More specifically, glycerol binds to the surface of ZrO 2 nanoparticles as a capping agent and prevents phase transformation during calcination. The crack-free ZrO 2 NF membrane exhibits a permeability of 13 LMH/bar and approximately 68% rejection rate when filtering NaCl solutions with mass fraction up to 24.92% [ 90 ]. Lu et al. have used zirconium salts and titanium alkoxides as sol-gel precursors to prepare a TiO 2 -doped ZiO 2 NF membrane [ 91 ]. The addition of Ti 4+ suppresses zirconia phase transformation, narrows the pore size distribution and increases the specific surface area. This membrane has high water permeability above 35 LMH/bar with a MWCO of 500 Da, and simulated retention rates of 99.6% for Co 2+ and 99.2% for Sr 2+ , indicating its attractive potential for radioactive wastewater treatment. Compared with alumina and zirconia membranes, the surface pore size and phase composition of titania membranes can be controlled by synthesis procedure. Anatase is the most preferable crystal form of titania due to its exceptional stability and narrow pore size distribution. A TiO 2 membrane with a pore diameter of 4 nm has been fabricated successfully by gentle heat treatment and remained stable in various solutions (brackish water, sea water and brine water) for over 350 h [ 89 ].

In addition to traditional metal oxide membranes, composite membranes made of two or more metal oxides is a current research focus. For example, a bilayer membrane containing a TiO 2 layer on top of a ZnAl 2 O 4 layer has been prepared and evaluated. It has been proved that compare to single layer membrane made from 50 mol% TiO 2 and 50 mol% ZnAl 2 O 4 with similar pore size, the bilayer membrane which has opposite surface charges could increase the electric interactions between membrane pores and filtered ions, and therefore produces a higher salt rejection, especially for divalent salts [ 112 ]. Another example of inorganic composite membranes is CoO-SiO 2 membrane synthesized by Elma et al. for desalination applications [ 94 ]. The effects of cobalt addition (up to 35 mol%), feed solution concentration (0.3–7.5 wt% NaCl), and operation temperature (22–60 °C) on purification performance were investigated systematically. Experimental results showed the volume fraction of silica mesopores increases with cobalt concentration, and with over 99.7% NaCl retention rate at all times, the highest water flux of 20 kg m −2 h −1 was achieved for 0.3 wt% feed solution at 60 °C. Furthermore, a series of studies confirm that silica membranes blended with cobalt oxide exhibit not only excellent desalination performance but also robust structures compared to single-element SiO 2 membranes [ 92 , 93 ].

In spite of prominent outcomes of metal oxide RO and NF membranes, certain shortcomings such as raw material cost and membrane thickness have hindered their commercialization for water purification. These issues can be overcome by further reducing the membrane thickness or exploring other cheap materials that have great chemical and thermal stabilities. Membranes that have strong surface charges in aqueous environment are also attractive.

2.2.2. Carbon-Based Membranes

In recent years, ordered mesoporous materials (OMMs) have attracted increasingly research interests in addressing water pollution and water shortage problems [ 113 , 114 ]. Among all kinds of OMMs, ordered mesoporous carbons (OMCs) such as carbon nanotubes (CNTs) and graphene possess important properties including large specific surface area, highly uniform structure with tunable pore size and strong atomic bonds, thus have been selected as promising candidates for wastewater treatment applications [ 115 , 116 , 117 ]. As one of fullerene derivatives, CNTs are cylindrical molecules composed of rolled-up graphite sheets with diameter ranges from 1 nm to several centimeters [ 118 ]. Based on the layers of graphite sheets, CNTs can be further classified into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs) and multi-walled carbon nanotubes (MWCNTs). For water desalination and purification applications, CNTs can be fabricated into standalone membranes or incorporated with other materials in many formats. An investigation of a highly stable and electrochemically active membrane made solely of CNTs, which could find significant applications in chemical and biological wastewater treatment, was undertaken by Sadia et al. [ 119 ]. Such CNTs membrane maintained a phenol removal rate over 85% for 4 h with an average oxidation rate of ~0.059 mol h −1 m −2 when operated with H 2 O 2 . Since water molecules can transport through CNTs structure without much impedance, some CNTs membranes used in RO systems with outstanding salt rejections as well as high water permeabilities have been reported [ 120 , 121 , 122 ]. On the other hand, the incorporation of CNTs into polymeric or inorganic matrix makes it possible to modify membrane properties and further improve surface hydrophilicity, fouling resistance, structural stability and salt retention. Yang et al. have confirmed a polyvinyl alcohol (PVA) based carboxylic MWCNTs membrane synthesized by interfacial adhesion method has better thermal stability and separation performance than a PVA membrane without carboxylic MWCNTs [ 123 ]. This PVA/C-MWCNT membrane exhibits a water flux of 6.96 kg m −2 h −1 and a NaCl rejection of 99.91% at 22 °C. In the work conducted by Peydayesh et al., hyperbranched polyethyleneimine modified MWCNTs were incorporated into polyethersulfone matrix to form a positively charged NF membrane, which had a average pore size of 0.81 nm and an enhanced water flux of 75.7 LMH [ 124 ]. The hybrid membrane showed superior retention rates for heavy metals (i.e., 99.06% for Zn 2+ , 94.63 for Ni 2+ , and 93.93% for Pb 2+ ) and antifouling property due to effective membrane surface charge and hydrophilicity, respectively.

Despite advantages of CNTs, drawbacks such as high cost and low selectivity for certain ions (arsenate, arsenic, and sodium) have limited their commercialization [ 118 ]. Graphene, a cost-effective two-dimensional carbon allotrope that consists of a monolayer of carbon atoms arranged in hexagonal lattice, has been found to be a highly permeable and selective material for water purification processes [ 125 , 126 ]. Since water flux across a membrane is inversely proportional to the membrane thickness, single-atom-thick graphene offers an opportunity for exceptional permeability and efficient energy utilization [ 127 ]. Pure graphene has a closely packed structure which is impermeable to gas and liquid molecules. Therefore to improve permeability and ion selectivity defects or functional groups must be generated designedly. Nanoporous graphene can be fabricated either by electrochemical modification of pristine graphene or by growth on supports from different chemical reactions [ 128 ]. The most commonly applied techniques to generate nanosized pores on graphene structure include high-temperature oxidation, ultraviolet (UV) ozone treatment and plasma etching [ 129 , 130 , 131 ]. Sub-nanometer-sized pores on monolayer graphene have been created successfully for nanofiltration and desalination applications [ 132 ]. During synthesis process, small defects were first introduced by ion bombardment and further enlarged by oxidative etching. The experimental results revealed that the separation mechanisms of the porous graphene membrane at short and long oxidation periods are electrostatic repulsion and streric size exclusion, respectively. Graphene oxide (GO), chemically converted from graphene nanosheets, has oxygen functional groups such as hydroxyl and epoxy which enable it to have better water dispersibility than graphene [ 133 , 134 ]. Nair et al. invented a GO membrane consisting of closed-packed GO sheets that only allow water molecules to travel through and concurrently hinder the motion of other species [ 135 ]. Similarly, Zhao et al. designed a free-standing GO membrane in which the GO sheets are crosslinked by Ca 2+ from Congo red dye [ 136 ]. More specifically, this GO membrane with tunable interlayer spacing was prepared by facile and thermal reduction methods using hot pressing method. Accompanied by relative high water permeability (17.1 LMH/bar), the resulting membrane showed excellent removal rates for heavy metal ions (i.e., 98.6% for Cu 2+ , 97.2% for Pb 2+ , 99.1% for Cd 2+ and 97.2% for Ni 2+ ). Although there have been many breakthroughs and exciting achievements for porous graphene and GO membranes in water filtration, special synthesis techniques for large-area porous membranes and fabrication reproducibility remain challenges towards commercialization.

2.3. Mixed Matrix Membranes

Mixed matrix membranes (MMMs), a currently popular area of research, are made by incorporating inorganic fillers into organic matrices. Although TFC membranes have excellent salt removal performance, there is a trade-off between permeability and selectivity. The main advantage of MMMs is to combine the low manufacturing cost, outstanding selectivity and high packing density of polymeric materials with long-term stabilities, high mechanical strength and regeneration capability of ceramic materials. One type of MMMs is a polymeric membrane blended with inorganic nanoparticles, which can be prepared by dispersion crosslinking, interfacial polymerization, or dip coating. Inorganic fillers that have been investigated for this purpose include titania, zeolite, silica, alumina, etc., and experimental results indicate the addition of inorganic nanoparticles alter the polymeric structures and effect the transportation of molecules through membrane pores [ 137 , 138 , 139 , 140 , 141 ]. Therefore it is not surprising that small inorganic nanoparticles would improve the water purification performance of organic membranes. Titania is widely used in anti-fouling coating due to its photocatalytic property. Kim et al. studied the influence of TiO 2 fillers on the properties of carboxylate groups functionalized TFC membranes and found the carboxylate groups help the adsorption of titania on TFC membrane surface, which result in very good anti-biofouling properties, especially under UV excitation [ 142 ]. Such a hybrid RO membrane also has stable surface structure since no significant loss of titania particles was observed after being tested for 168 h [ 143 ]. Researchers also recognized the addition of zeolite and silica nanoparticles increases the surface roughness, contact angle, and water flux [ 144 , 145 ]. NaA zeolite nanoparticles are the first successfully synthesized zeolite particles with low contact angle (<5°) and RO ranged pores (~0.5 nm) [ 146 ]. MMMs prepared with NaA zeolite fillers by interfacial polymerization method have many outstanding properties, that is, more negatively charged and hydrophilic surface with increasing zeolite content, enhanced water permeability, and better water purification performance [ 147 ].

Composite membrane synthesized from carbon-based materials and organic materials is another type of MMMs. Majumder et al. reported a polystyrene membrane incorporated with MWCNTs which have an average diameter of 7 nm [ 148 ]. The MWCNTs were grown and aligned by catalytic chemical vapor deposition (cCVD) method, followed by spin coated on polystyrene matrix to seal gaps between CNTs. The tips of MWCNTs were opened by plasma etching approach, and the water flux of the synthesized composite membrane was 4–5 orders of magnitude higher than that calculated from Hagen-Poiseuille theory, indicating macroscale hydrologic mechanism. On the other hand, some researchers explained the ultra-high water flux was due to the formation of a layer of water molecules along MWCNTs walls, which reduce the friction significantly when bulk mater molecules come through [ 149 ]. Furthermore, to simplify the complex fabrication steps of MMMs, a patient has been published recently about dispersing 0.8 nm diameter CNTs into cross-linking solutions during the formation of polymeric membranes, so that the CNTs can be embedded into the organic barrier layer on top of microporous polyethersulfone support [ 150 ]. After being functionalized by octadecylamine, tests were performed on membranes made with and without CNTs to demonstrate the improved water flux generated by CNTs pathways. Experimental results showed the flux of membrane containing CNTs was approximately twice as much as that without CNTs (44 L m −2 day −1 bar −1 compared with 26 L m −2 day −1 bar −1 ), and MMMs with CNTs also had a slightly better salt rejection (97.7% compared with 96.2%). Even though MMMs combine the benefits of both polymeric and ceramic membranes, they are difficult to study since the interface between various materials may have unwanted structure and certain great materials become insoluble in each other. In addition, studies on MMMs with larger surface area are necessary before developing manufacturing apparatus for large-scale production.

3. Challenges and Future Perspectives

Although the water purification market has been occupied by polymeric membranes for more than 10 years, research and development activities in polymeric membranes are reaching the bottleneck and many industries still use traditional TFC membranes such as PA membrane which was introduced nearly 40 years ago. Despite expansions of TFC membranes and related techniques, it is time to upgrade RO technology to a new height or develop another cutting-edge technology for water purification. Addition of functional materials such as inorganic fillers, lyotropic crystals, CNTs, MWCNTs, and aquaporins can optimize the water flux and/or salt rejection, but the high cost issue associated with synthesis and blending these materials needs to be addressed before scale-up production and commercialization [ 151 , 152 ]. Meanwhile, new models are needed to predict the performance of composite membranes. Traditional polymeric RO and NF membranes are commonly modeled based on extended Nernst-Planck equation, which needs to be modified for carbon-based MMMs [ 153 ]. Recent models applied to calculate water flux and salt rejection of charged membranes for aqueous electrolyte solutions are listed in Table 5 . For organic membranes blended with CNTs, CNTs can be simplified as circular cylinders, the fluid transport of which can be modeled using Hagen-Poiseuille equation. The flow through pores outside the CNTs and within the polymeric matrix can still be studied by extended Nernst-Planck model concerning dielectric exclusion since the dielectric constants for feed water, CNTs and organic matrix are different and electrostatic interactions will happen between ions in feed solution and polarization charges formed along the boundary of various dielectric media [ 154 ]. Assuming that the CNTs are distributed uniformly in polymeric base, the predicted model for such MMMs is likely to be extended Nernst-Planck formula plus an additional Hagen-Poiseuille term. Both terms are re-written according to their corresponding concentration before addition. The modeling of MMMs with GO fillers is more complicated and depends on the insertion direction: if GO is blended vertically into organic membrane like CNTs, similar equation of CNTs MMMs can be used for GO MMMs; If GO is added horizontally, the tortuosity factor in the extended Nernst-Planck equation needs to be revised due to the fact that the ion transport path inside GO is different from that in polymeric matrix. Additionally, since the functional groups located on the surface of GO (types of functional groups are determined by synthesis method, precursor materials, etc.) can react with ions in fluid and form complexes, the flux and permeability may change with time, indicating possible process-model mismatch. On the other hand, advanced techniques including rapid thermal processing (RTP) and nanorods fabrication enable the generation of defect-free membranes for water treatment applications. In addition to the use of new materials and leading-edge technologies, membrane diameter also plays an important role in enhancing filtration performance. Membranes with large surface area could reduce capital cost and energy consumption by approximately 15% [ 68 ]. Furthermore, different water treatment plants have specific difficulties to overcome. For instance, low recovery rate of seawater, disposal of brine and high capital cost are the biggest challenges that nowadays desalination plants confront. Tarquim et al. have developed a method to minimize produced brines, which results in good recovery rate, but more research and equipment are needed to reduce brine disposal [ 155 ]. Moreover, integration of traditional synthesis process with renewable energy may make green fabrication of nanocomposite membranes possible.

Recent models for transport of aqueous electrolytes through charged membranes.

The excellent filtration performance of inorganic membranes, as stated in Table 4 , indicates the capacity of ceramic membranes for most water purification applications, and the low acceptance of inorganic membranes in the past is because of the sheer dominance of polymeric RO and NF membranes in large-scale water treatment systems. Recent research on preparation of advanced inorganic membranes such as free-standing CNTs membranes and interlayer free membranes enables efficient filtration process with better purification performance and lower facility cost [ 8 , 162 ]. According to Weschenfelder et al., the operation expense and total cost of a water treatment plant using ceramic membranes with a flow rate of 2 m/s and water recovery rate of 95% are US $0.23/m 3 and US $3.21/m 3 , respectively [ 163 ]. Similar to polymeric membranes, the development and manufacturing costs of ceramic membranes remains a significant problem for their industrialization. For example, although there have been rapid growth and development for CNTs and MWCNTs membranes in laboratory-scale, the commercial applications of carbon-based membranes are ongoing in a low pace due to the high cost of synthesizing CNTs and MWCNTs. Thanks to recent advancements in fabrication technology including cCVD, large-scale synthesis of high-quality CNTs economically is achievable. However, the reproducibility and feasibility of these methods for making membranes are in doubt. For traditional metal oxide membranes, high cost of supports is a challenging issue for commercialization. Current research focuses on studying alternative inorganic membranes made from cheaper or waste materials such as coal fly ash to reduce the manufacturing investment.

4. Conclusions

Tremendous amount of effort has been made to overcome the clean water scarcity and nanotechnology is a strong candidate with fast development. Study and commercialization of polymeric RO and NF membranes started in the early 1960s. So far the water desalination market is dominated by two kinds of membranes: cellulose-based (CA) membranes and thin-film composite (TFC) membranes. The most representative products such as TS40, TS80 and AD-90 were developed more than 30 years ago and due to their low manufacturing costs and high salt rejections, no major change has been made since then. New research directions for barrier layers in TFC membranes include improvement of fouling resistance as well as chemical and thermal stabilities. Meanwhile microporous supports can be optimized to increase the mechanical strength and permeability.

Inorganic RO and NF membranes have been studied in lab scale for water purification since the 1980s. The most representative ceramic membranes are metal oxide membranes and carbon-based membranes. The main synthesis method for metal oxide membranes is sol-gel technique, which needs further optimization to control the particle size and distribution. The performance of mixed matrix membranes (MMMs) made with both organic and inorganic nanomaterials is excellent, yet they are too expensive compared with other membranes. Hence it is important to realize the economic competitiveness of MMMs, as well as their potential applications. While nanotechnology is leading the way in developing RO and NF membranes for water purification, there are still technical and scientific problems that need to be solved before more benefits can be realized. Despite the challenges to be overcome, it is highly possible that ceramic membranes will be commercialized and industrialized in water purification and desalination fields in the near future.

This research received no external funding.

Conflicts of Interest

The author declares no conflict of interest.

Appropriate household point-of-use water purifier selection template considering a rural case study in western India

• Review Article
• Open access
• Published: 30 April 2020
• Volume 10 , article number  124 , ( 2020 )

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• Ramprasad Venkatesha 1 ,
• Anand B. Rao 2 &
• Shireesh B. Kedare 3  

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There is a wide range of household water treatment options available for a variety of contexts. Each water purifier has its own optimal range of operation. Simultaneously, the diverse environments and circumstances set different boundary conditions for such purifiers to operate successfully. In low-income countries, especially with unregulated and decentralised water supply mechanisms such as open wells, the use of point-of-use water purifiers is quite widespread. However, it is observed that the water purifier may not be appropriate to the prevailing context. Hence, this short review aims to introduce a wide range of water purification alternatives available for a family (of about 3–5 members) and the way they could be classified and reviewed. The perspective selected is that of a low-income rural household in coastal region of western India and the scenario of water quality which is primarily affected by physical and biological impurities and not necessarily severe chemical contamination. Based on this context, attributes are defined and prioritised; further, a scale to rate the purifiers is worked out. A selected number of point-of-use water purifiers for which data from the literature or field observations are available are reviewed against these attributes for the sample context chosen. This independent review methodology consists of setting the attributes and comparing the water purifiers based on the sum of prioritised scores and thus acts like a selection template and can be adopted to select the appropriate purifier for any other scenario accordingly.

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Introduction

The global population which did not have access to safe drinking water in the year 2012 was around 700 million. With household treatment of water, it has been reported that diarrhoeal illnesses could be reduced by 30–40% (Sobsey et al. 2008 ). In India, it has been observed that 70% of the surface water is microbiologically and chemically contaminated. Further, more than 33% of ground water sources in rural India is claimed to be polluted (Water Pollution 2013 ).

In rural areas due to the dispersed settlements, drinking water sources are usually decentralised in the form of dug wells, hand pumps or tube wells. Even in urban areas, despite the existence of centralised water supply, marginal communities may lack the access to such utilities or supply through such centralised systems may be prone to get contaminated. In such scenarios, household point-of-use water purifiers become indispensable. A review of such purifiers might be quite useful to zero in on the most suitable purifier for the prevailing context and hence this study.

Point-of-use purifiers which incorporate water treatment at or near the place of use are covered in the study. This study, primarily undertaken through the review of the literature, classifies and describes the different types of PoU purification alternatives for a family (of about 3–5 members). Based on the perspective of a rural household consuming water from a decentralised source, such as an open well in the coastal region of Maharashtra State in western India, the attributes used to compare the water purifiers are prioritised. Further, the study compares a selected number of point-of-use purifiers across different attributes, for which relevant data from the literature and field observations were available. This independent reviewing approach, considering various references, helps in identifying the water purifier which gets the highest total score which is to be considered the appropriate water purifier for the prevailing scenario. Finally, this review comes up with some emerging inferences.

Classification and description of point-of-use water purifiers

Classification of water purifiers.

The classification of purifiers has gradually evolved, and the description and methodology adopted in this review takes references from Peter-Varbanets et al. ( 2009 ) and Loo et al. ( 2012 ). The purifiers have been categorised into thermal- or light-based treatment techniques, physical removal methods, chemical treatment techniques and integrated water purification. Both sections on classification (“ Classification of water purifiers ” section) and description (“ Description of purifier alternatives “ section) cover a wide variety of water purification options; however, a special focus has been accorded to feasible options in the context of decentralised water sources prevalent in rural coastal areas in developing countries such as India. Most of the water purifiers in use or available in the market usually combine different treatment techniques and hence are integrated water purification methods. However, to make it clear to the reader the underlying water purification methodology, the classification in terms of the technique used for purification is adopted. The detailed classification chart is as shown in Fig.  1 .

Hierarchical chart depicting the classification scheme of the study

Description of purifier alternatives

Thermal or light based treatment techniques.

Boiling is perhaps the oldest method of water purification (Sobsey 2002 ) but is a highly energy intensive one. One minute of boiling at a temperature 100 °C (at mean sea level) ensures neutralisation of faecal and thermo-tolerant coliforms, protozoan cysts and viruses (Sobsey 2002 ; Loo et al. 2012 ). Since boiling does not provide residual protection, boiled water needs to be kept in closed and clean containers and preferably consumed within 24 h. The taste of water after boiling gets altered and is generally not easily adopted across all regions except in Asia due to sociocultural reasons (Lantagne and Clasen 2009 ).

Thermal pasteurisation

In thermal pasteurisation, temperature usually does not go beyond 75 °C which is suitable to eliminate E. coli by more than 5 LRV (Islam and Johnston 2006 ; Gupta et al. 2008 ). Coiled metal tubes can be retrofitted with cookstoves (Fig.  2 ) as in traditional earthen cookstove or Chulha in Chulli purifier or Lonera cookstove in water disinfection stove (WADIS). Due to its difficulty in use and mechanical issues, its adoption was limited in Bangladesh (Gupta et al. 2008 ; Loo et al. 2012 ).

Chulli purifier in the form of a coiled tube (Islam and Johnston 2006 )

It has been reported that up to 4 LRV of faecal coliform and viruses could be removed using solar water heaters with solar irradiation of just 2 h on sunny days and 4 h on cloudy days (Kang et al. 2006 ; Loo et al. 2012 ).

Solar distillation

Solar distillation combining the process of evaporation and distillation can be a convenient method for the removal of salts and non-volatile impurities using solar stills (Flendrig et al. 2009 ). Solar still consists of a vessel which holds the contaminated water and a transparent lid which aids condensation (Flendrig et al. 2009 ) (Fig.  3 ). This method involves large area, high upfront cost and low discharge rates of 0.5 L/d to 3 L/d (Flendrig et al. 2009 ; Loo et al. 2012 ).

Conceptual sketch of a solar distillation unit (Loo et al. 2012 )

Solar disinfection (SODIS)

For low volumes of filtered water with turbidity of less than 30 NTU, water can be filled in transparent polyethylene terephthalate (PET) bottles (Fig.  4 ) and kept under sunlight for at least six hours after forceful shaking for aeration (Peter-Varbanets et al. 2009 ). SODIS can be an effective way to use heat and UV radiations from the sun to targets microbes. In case of low intensity of solar radiation, solar collectors or additives like lemon juice or vinegar can be used to improve the efficacy (Loo et al. 2010). SODIS has low operating costs involved because easy availability of PET bottles, however, has a long treatment time on low volumes of water.

SODIS in operation (SODIS, 20.11. 2019 )

Ultraviolet (UV) treatment

For low turbid water UV treatment could be effective even on Crypto Giardia lamblia cysts and Cryptosporidium parvum oocysts by more than 3 LRV (Gadgil 1998 ; Berg 2010 ). UV systems generally rely on electrical power and do not offer residual protection (Berg 2010 ). Aquaguard Compact (Fig.  5 ) is an example of UV-based purifier (Aquaguard, 28.10. 2014 ).

Aquaguard Compact UV purifier (Aquaguard, 28.10. 2014 )

Chemical treatment techniques

Chlorination

Chlorination is a simple, affordable and scalable method of water disinfection through the use of sodium hypochlorite NaOCl (liquid) (Fig.  6 ), NaDCC (solid) and calcium hypochlorite (Ca(OCl) 2 ) (solid). It gives residual protection due to the availability of free chlorine; however, there may not be any improvement in terms of turbidity. With a dosage of 2 mg/L for about 0.5 h, chlorination can offer about 3 LRV of enteric bacteria (Gadgil 1998 ); however, there is the issue of generation of disinfection by-products (DBPs).

Plastic bottle containing sodium hypochlorite solution. Photo: Darpan Das, based on special arrangement with the authors

Combined flocculation/coagulation and disinfection (CFD/CCD)

For a reduction in turbidity as well as microbial disinfection, combined methods such as coagulant/flocculant as well as chemical disinfectant powders/tablets are used (Peter-Varbanets et al. 2009 ). These products (like PuR sachet in Fig.  7 ) combine calcium hypochlorite (or bleach) with coagulating agents like sodium carbonate and oxidisers like potassium permanganate. For 10 L of water, a PuR sachet of 4 g is added, stirred for 5 min and after sedimentation, and the water is filtered across a clean fabric and left undisturbed for 20 min for disinfection (CDC, 28.10. 2014 ). The method could offer 7–9 LRV for bacteria, 2–6 LRV for viruses and 3–5 LRV for protozoa (Sobsey et al. 2008 ). Flocculation–disinfection also has the problem of taste and odour like chlorination but also involves higher cost, multiple steps and resources (Lantagne and Clasen 2009 ).

Combined flocculant–disinfection (PUR) sachet (PUR, 31.10. 2014 )

To remove particulates, organic matter and chlorine/disinfectant leftovers, adsorbents like activated carbon are used. They are used in granulated form after disinfection methods like chlorination, UV, etc. like in commercial purifiers like Aquaguard Compact and HUL PureIt Classic (Aquaguard, 28.10. 2014 ; Pureit, 28.10. 2014 ) (Fig.  8 ). Biofilm growth compels frequent replacement of such cartridges (Peter-Varbanets et al. 2009 ). In Tata Swach, adsorption is through rice husk ash (activated silica and activated carbon) which is impregnated with silver nanoparticles to target microbes (Swach, 28.10. 2014 ).

Tata Swach Cristella Plus and HUL Pureit Classic (Swach, 28.10. 2014 ; Pureit, 28.10. 2014 )

Physical removal methods

Sedimentation or clarification.

Clarifiers like alum, lime, iron, seeds of Moringa oleifera (drumstick) (Fig.  9 ) and seeds Strychnos potatorum (clearing nut or Nirmali tree) (Fig.  10 ), Guar gum and Jatropha curcas have been used to reduce turbidity through sedimentation (Ndabigengesere and Narasiah 1998 ; Sobsey 2002 ). There are also claims that Strychnos potatorum and aluminium salts (alum) and iron salts could help in reduction in microbial contamination by up to 95% and 99%, respectively (Sobsey 2002 ; Khan et al. 1984 ).

Moringa oleifera tree and dried seed (unpeeled and peeled) (Moringa Tree, 30.10. 2014 )

Strychnos potatorum (clearing nut) seeds (Clearing nut, 31.10. 2014 )

Membrane based treatment methods

In these methods, filtration occurs across a semi-permeable membrane due to gravity or a difference in pressure, osmotic potential, temperature or electric potential (Mulder 2000 ). Depending on the pore size, microfiltration (0.1–1 µm) can retain only bacteria, ultrafiltration (0.005–0.1 µm) can remove both bacteria and viruses, nanofiltration (0.5–5 nm) cannot retain salts, while reverse osmosis (0.15–0.5 nm) can even filter out salts (Fig.  12 ) (Peter-Varbanets et al. 2009 ) (Fig.  11 ).

Different membrane purification regimes, the respective pore sizes and the particles that can be removed (Peter-Varbanets et al. 2009 )

Paper, fabric and fibre filters

Considering the pore size of paper and fabric filters, only pathogens like Vibrio cholera can be filtered to a extent of 95–99% (Sobsey 2002 ). Those made with multiple layers of polyester or nylon could remove cyclops and zooplankton (Agrawal and Bhalwar 2009 ). Up to 6 LRV of Escherichia coli and 3 LRV of Enterococcus faecalis , the removal is possible through bactericidal papers impregnated with silver nanoparticles due to inactivation offered by silver (Loo et al. 2012 ).

Microfiltration (MF)

There are ceramic- and polymer-based microfiltration systems. In ceramic filters (Fig.  12 ), clay is mixed with burnout material to make porous ceramic filters of varied shapes with pore size of about 0.2–3.0 mm depending on the sophistication of manufacture (Sobsey et al. 2008 ). These ceramic filters could be locally made and coupled with silver impregnation to provide disinfection. The efficiency of removing bacterial and protozoan contaminants is significant (2–6 LRV and 4–6 LRV respectively); however, it is not so significant on viruses (0.5–4 LRV) (Sobsey et al. 2008 ). These filters can help in visible reduction in turbidity, however, needs to be cleaned and handled safely (Loo et al. 2012 ). Katadyn Mini, Potters for Peace pot-based clay filter (PFP, 28.10. 2014 ) and Terafil filter (Terafil, 28.10. 2014 ) are all a silver impregnated ceramic filters.

Ceramic filter system and element in different forms (Simonis and Basson 2011 )

There are polymer-based microfiltration devices like FilterPen whose polymer size is about 0.15 mm with a surface area of 0.02 m 2 (Peter-Varbanets et al. 2009 ).

Coated textile candle filter is another example for microfiltration. After regular prefiltration and activated carbon treatment, water is passed through a coated textile candle which claims to remove pathogens larger than 1 µm and further ruptures microbes; however, the disinfection level is not specified. The whole setup is housed in PET containers (Fig.  13 ) (Livinguard, 29.10. 2014 ).

Livinguard Rural Filter (Livinguard, 29.10. 2014 )

Ultrafiltration (UF) and nanofiltration (NF)

With much lesser pressure potential, ultrafiltration and nanofiltration techniques can ensure a complete microbial removal (Peter-Varbanets et al. 2009 ). Although inlet water quality does not significantly affect the performance, periodical backwashing is required to prevent fouling. Some of the popular devices are Lifestraw (Lifestraw, 28.10. 2014 ) (Fig.  14 ), wherein purified water is sucked from a vessel containing impure water (Loo et al. 2012 ). Another product named Lifesaver bottle (Fig.  15 ) claims to achieve 7.5 LRV against bacteria and 5 LRV against viruses and treats about 4000 L of water (Lifesaver, 28.10. 2014 ).

Lifestraw in operation (Lifestraw in use, 31.10. 2014 )

Lifesaver bottle (Lifesaver, 28.10. 2014 )

Pedal-operated UF purifiers have also been attempted like He ( 2009 ), Saini et al. ( 2013 ) (Fig.  16 ) and BARC (28.10. 2014 ) where pressure of 4 bar generated through pedalling motion can accelerate discharge rate to about 36 L/hour (Saini et al. 2013 ). These systems greatly help in improving the visibility of water by reducing turbidity (44.7 NTU to 0.267 NTU) and TDS along with microbial (total coliform count from 300 cfu/100 mL to < 1 cfu/100 mL) (He 2009 ).

Pedal powered UF system. Photo: Ramprasad V

There are modular variants of UF purifiers which are suitable for community scale like SkyHydrant, Lifestraw Family and also mobile variants like Jaldoot and Perferctor E (Loo et al. 2012 ; Peter-Varbanets et al. 2009 ).

Several stationary household UF purifiers are available like Moselle (Fig.  17 ), Jaltara (Fig.  18 ) and Waterife Little Star Gold (Moselle, 29.10. 2014 ; Jaltara, 29.10. 2014 ; Waterlife, 29.10. 2014 ).

Moselle purifier (Moselle, 29.10. 2014 )

Jaltara filter (Jaltara, 29.10. 2014 )

There is a unique experiment with plant xylem-based ultrafiltration. Bacteria up to 3 LRV can get filtered out with sapwood (predominantly xylem) of trees like pine which is easily available, inexpensive, biodegradable and suitable for resource-constrained environments (Boutilier et al. 2014 ). A small branch of a pine tree is peeled and then inserted into a tube and clamped to make the filter (Fig.  19 ). Achieving high flow rates is difficult; however, a volume of 3 cm 3 of sapwood can meet the needs of an individual (Boutilier et al. 2014 ).

Preparation of the plant xylem purifier (Boutilier et al. 2014 )

Biopolymer-reinforced synthetic granular nanocomposites

Reverse osmosis (ro).

RO with pore size of < 1 nm and high water pressure filters out all types of pathogens and waterborne impurities (Fig.  20 ) (Loo et al. 2012 ). To avoid RO membranes getting fouled, prefiltration such as sedimentation, microfiltration and activated carbon filters (also in post-filtration) are adopted. RO-based water purifiers are generally expensive. RO systems can be coupled with photo-voltaic systems to power them (Loo et al. 2012 ) and can be mounted on vehicles to make them mobile (Peter-Varbanets et al. 2009 ).

Reverse Osmosis Purifier (Kent RO, 31.10. 2014 )

Most RO purifiers are integrated water purifiers with methods such as microfiltration, ultrafiltration and ultraviolet treatment in conjunction with reverse osmosis based water filtration.

Forward osmosis (FO)

In forward osmosis, a bag (e.g. Hydro Pack) made of semi-permeable membrane is filled with concentrated sugar solution and then dipped in impure water (HTI, 29.10.2014). Due to the osmotic potential, water enters the pouch and contaminants get trapped outside the bag (Fig.  21 ). The diluted sweet water packed with nutrients and minerals can be consumed directly (Peter-Varbanets et al. 2009 ). However, this method is suitable for individuals during emergencies, considering its high cost and low yield.

Forward Osmosis X-Pack (HTI, 20.11. 2019 )

Biosand filter

A biosand filter (BSF) consists of a container packed with sand where a biologically active layer (schmutzdecke) is allowed to develop on the top surface (Fig.  22 ) which restricts the passage of bacteria by around 2 LRV and protozoa by more than 3 LRV and viruses by about 1 LRV (Sobsey 2002 ; Peter-Varbanets et al. 2009 ). BSF can remove 95% turbidity and gives a discharge of about 20 L/hour (Peter-Varbanets et al. 2009 ). A diffuser plate is placed on bio-layer to avoid disturbance of schmutzdecke and the user just pours in water on top of the diffuser plate and collects filtered water from the outlet. NEERI - Zar developed by CSIR-National Environmental Engineering Research Institute (NEERI) is also a type of modified sand-based water filter (NEERI, 22.04. 2017 ).

Cross section of a biosand filter (Biosand, 31.10. 2014 )

Integrated water purification

Considering the advantages and limitations of different water treatment methods, some of the household water purifiers combine multiple types of water treatment techniques. For example, the RO systems generally are supported by microfiltration, ultrafiltration and ultraviolet treatment techniques. There are also some mobile purification units comprising of multiple methods of water treatment like micro-hydraulic mobile water treatment plant (MHMWTP) which have been developed. MHMWTP incorporates chlorination, sedimentation, filtration and optional granular-activated carbon (GAC) treatment (Garsadi et al. 2009 ). Similar mobile system is Jaldoot (Fig.  23 ) which involves multiple treatment mechanisms ranging from pressurised sand filtration, GAC module, microfiltration and ultrafiltration all integrated into one unit on a three-wheeler. This unit is capable of delivering 1500 L every hour (Jaldoot, 29.10. 2014 ).

Jaldoot mobile purifier (Jaldoot, 29.10. 2014 )

Another example of integrated water purification is microfiltration coupled with biopolymer-reinforced synthetic granular nanocomposites which release silver ions in water offer arsenic and microbiological disinfection at a low cost (Sankar et al. 2013 ). The system has a discharge rate of 10 L/hour and purifies 3600 L of water (Sankar et al. 2013 ) (Fig.  24 ).

Schematic diagram of the purifier prototype (A) and its actual photograph (B) (Sankar et al. 2013 )

Review of purifier alternatives

Attributes selected for review.

The reference for different attributes which evaluate the purifiers was primarily followed as in Peter-Varbanets et al. 2009 and Loo et al. 2012 . However, the list of attributes and their priority (Table  1 ) was selected based on their relevance to a low-income rural context. Specifically, the context is that of a coastal rural area in a developing country like India, wherein there were no major chemical contaminants identified in the decentralised water sources, mostly open wells.

The finalised list of attributes (and the reference for scoring) is selected for review as follows.

Sustainability (Peter-Varbanets et al. 2009 )

Purification performance (Peter-Varbanets et al. 2009 )

Rate of production (Peter-Varbanets et al. 2009 )

Maintenance (Peter-Varbanets et al. 2009 )

Energy requirement or dependence on utilities (Peter-Varbanets et al. 2009 )

Ease of use (Peter-Varbanets et al. 2009 )

Portability/ease of deployment (Aggregated from multiple sources including local references, primarily Loo et al. 2012 )

Supply chain requirement (Loo et al. 2012 )

Cost (in Rs/L) (Lifetime and investment adjusted) (Aggregated from multiple sources including local references, primarily Peter-Varbanets et al. 2009 )

Social acceptability (Peter-Varbanets et al. 2009 )

The above attributes can further be broadly classified based on the categories proposed by Pagsuyoin et al. ( 2015 ) into technological performance, environmental sustainability, economic viability and social acceptability. This is a simpler way of integrating the attributes for a given context. Based on the categorisation, the following attributes: purification performance, rate of production, maintenance, energy requirement or dependence on utilities, ease of use, portability/ease of deployment and supply chain requirement will mostly get categorised under technological performance. Further, sustainability, cost and social acceptability would get categorised into environmental sustainability, financial viability and social acceptability, respectively.

However, it is to be noted that this broad categorisation of attributes is simplistic and not exactly as proposed in Pagsuyoin et al. ( 2015 ). Since the scores for different attributes selected were mostly from Peter-Varbanets et al. ( 2009 ), Loo et al. ( 2012 ) and other sources, an independent methodology for review, hve been adopted.

Alternatives selected for review

The classification of water purification techniques in “ Classification of water purifiers ” section represents an overall academic approach to illustrate wide spectrum of options possible with a special focus towards possibilities in the context of decentralised water sources as in rural coastal areas in developing countries like India. However, to adopt a more practical approach for identifying the appropriate water purifier for a given scenario, the water purifiers for which sufficient information from primary sources (field observations) and secondary sources (literature review) was available were chosen for review. A thorough literature review was undertaken from multiple references, but primarily from Peter-Varbanets et al. 2009 and Loo et al. 2012 . The purifiers for which sufficient information for comparison against all attributes was chosen were as follows:

Household boiling

Solar stills

Solar disinfection

UV-based purifiers

Combined coagulation–disinfection (PuR sachet)

Biosand Filter

Household Ceramic Filters

Portable UF (Lifesaver bottle)

Bicycle powered UF

Small-scale Reverse Osmosis

FO reusable filter pouch

Analysis of review of alternatives

This section presents a detailed comparison based on preferential scores assigned for each purification method based on its performance against a particular attribute. The attributes have been accorded priority considering a low-income rural household as the case in focus. Several visits to Ransai, Vavoshi and Shiroshi villages on Pen-Khopoli road in Raigad District of Maharashtra State in India were undertaken with support from a social organisation named Rural Communes. Similarly, several visits to villages near Ganeshpuri in Palghar district of Maharashtra State in India were undertaken with support from a social organisation named Shree Nityananda Education Trust (SNET). Based on extensive visits to these villages, observation of water sources, feedback from villagers and discussions with teams of social organisations, the attributes used to rate the purifiers were accorded priority. Physical filtration of turbidity and removal of pathogens turned out to be some of the key needs of the villages. This formed the specifics of the context of the review methodology: a rural setup in the coastal area in a developing country like India wherein open wells are the primary water sources and the primary concerns of water quality are mostly physical (turbidity) and biological (microbial contamination). No specific chemical contamination has been focused in the review as no such major issue was identified in the field area under consideration.

The purification methods have been assigned scores based on their performance again each attribute out of a total score of 3. Finally, the total score of each purification method is calculated by summing up the product of the score against a particular attribute and the attribute’s priority (Table  2 ).

Description of score rating of purifiers against each attribute

Purification performance against pathogens

Purification performance is microbial removal efficiency against pathogens. This attribute primarily considers performance in terms of effectiveness in the removal of bacteria. This was observed as one of the key needs in the villages surveyed apart from physical treatment in terms of turbidity. While turbidity does not have immediate adverse impact over the health of the people, the removal of pathogens is one of the critical needs; hence, this attribute has been assigned the highest priority of 6 out of 6 (Table  1 ). Apart from boiling, coagulation–disinfection, RO, FO, UV and UF, there seem to be no “foolproof” method of microbial disinfection; hence, these have been assigned a score of 3 out of 3. All of these are expensive except boiling when firewood is easily available and hence probably indicates the huge dependency of rural areas on boiling. The remaining purification techniques are assigned a score of 2 out of 3.

Cost Rs/L (lifetime and investment adjusted)

In the villages which were considered, cost is a crucial consideration in the adoption of any water purifier because population is mostly composed of low-income households. Hence, once again the highest priority of 6 out of 6 has been assigned to the cost attribute (Table  1 ). Each purifier has a time limit within which the purifier’s operational efficiency is acceptable. To take into account the investment and operational costs of the purifier over its lifetime, cost is calculated for every liter of water purifier based on the information of lifetime of the purifier available through the literature or through field-based observation. The ratio of purifier’s investment cost to the volume purified over its lifetime is summed up with the operational cost over the purifier’s lifetime in consistent units and presented as a single attribute as cost in Rs/L. (This review assumes a conversion rate of 1 US$ = INR Rs.60.) In this regard, sand/ceramic-based and chlorination-based purification is the cheapest (score 3 out of 3), while UF, solar stills, RO and FO are quite expensive (score 1 out of 3). The remaining purification methods have been assigned a score of 2 out of 3.

Rate of production

This attribute implies the ability to cater to increased demands of water within a short period of time. Boiling, SODIS, chlorination and combined coagulation–disinfection can be scaled up and down to meet the flexible demands, methods like UV, household UF, bicycle UF and RO have production rates of > 10 L/hour; hence, these have been assigned a score of 3 out of 3. Solar distillation and forward osmosis have < 0.1 L/hour (score 1 out of 3), while purifiers like Tata Swach, HUL Pureit, ceramic, biosand filter, Terafil and Lifestraw have discharge rates which are in between 0.1 and 10 L/hour (score 2 out of 3). If the rate of production is too low, it often renders the purifier unusable; hence, this attribute is also assigned a high priority of 6 out of 6 (Table  1 ).

Ease of use

If a purifier is convenient to handle and use, there are higher chances of its continued usage. Based on the field observations, it was inferred that ease of use for the community matters quite heavily in terms of purifier’s continued usage. Hence, this is assigned a priority of 4 out of 6 (Table  1 ). Referring to Peter-Varbanets et al. ( 2009 ), some qualitative scores have been assigned as follows. A score of 3 (out of 3)/++ is given for most purifiers which can be handled easily and which require only filling of feed water and collection of purified water. A score of 2 (out of 3)/+ is allocated if any extra effort is required like chlorination and combined coagulation–disinfection demand stirring, boiling requires heating, SODIS and solar distillation require effort to place the purifiers under the sun and bicycle UF requires pedalling.

Maintenance

It is often seen in the field areas that once a water purifier is handed over to a rural community, its proper maintenance is often neglected. Improper maintenance may cause the purifier to malfunction, and hence, maintenance is accorded a priority of 4 out of 6 (Table  1 ). Maintenance in some form is required for all purifiers while the most common being cleaning water holding containers. Other maintenance operations include back flushing of membrane filters, removing depositions on candle filters and scraping off the top layer of sand in biosand filters. There is replacement of chemicals in chlorination, combined coagulation–disinfection and FO, while there is replacement of cartridges/membranes in ceramic microfiltration, household UF, bicycle UF and RO methods. Boiling, solar stills, SODIS, BSF, chlorination and combined coagulation and disinfection require the basic amount of maintenance and have been given score 3 out of 3 as the purifier would not severely malfunction in the absence of maintenance. Ceramic filters, UV and FO pouches require inexpensive replacements and hence have been given a score of 2 out of 3. RO and UF hugely depend on expensive module replacements and hence have been given a score of 1 out of 3.

Energy requirement or dependence on utilities

Different purification methods are dependent on different energy utilities, and this attribute needs to be considered for rural areas. Since it is observed that energy constraints are often prevalent in rural settings, this attribute is accorded a priority of 4 out of 6 (Table  1 ). Boiling requires fuel; UV and RO depended on electricity and hence have been assigned a score of 1 out of 3. UF systems require mechanical effort and SODIS & household stills depend on sufficient solar radiation and have been given a score of 2 (out of 3). The other methods do not need any external energy or depend on gravity and osmotic potential for their energy requirements and hence have a score of 3.

Ease of deployment

The ease of deployment is quite relevant in remote circumstances. Since ease of deployment plays a major role in handling of the purifier during deployment as well as shifting which could be common in a rural setting, this is assigned a priority of 2 out of 6 (Table  1 ). Purification methods which can be easily deployed and used (boiling, SODIS, chlorination, CCD, household UF, FO) have been given a score of 3 out of 3. However, if the purifier’s sophisticated make-up hampers its rugged use, then a value of 2 out of 3 is assigned. For example, biosand filter being bulky and taking considerably long start-up time and purifiers like solar stills, UV, RO and ceramic filters being delicate and prone to damage during handling/transporting.

Sociocultural acceptability

In the selected villages for the study, it appeared that sociocultural acceptability appeared to be an important consideration which cannot be neglected in terms of adoption of purifiers. Social acceptability has been assigned a priority of 2 out of 6 (Table  1 ). Boiling being the only traditionally practised method is given a score of 3 (out of 2). Most purifiers which were accepted when deployed (ceramic, UV, biosand, household UF and FO) have been assigned a 2 marks out of 3. Although chlorination and combined coagulation–disinfection have been in use for quite some time, they produce bad taste and odour. Some purifiers like SODIS have not been readily accepted even after deployment; further, bicycle-based UF requires some investment and pedalling effort and RO requires higher investments and electricity and hence have not been fully accepted. These methods have been assigned a score of 1 (out of 3).

Environmental sustainability

Environmental sustainability is difficult to quantify and can be sometimes subjective; however, usage of any purifier has environmental implications which is quite important to consider. Referring to Peter-Varbanets et al. ( 2009 ), some qualitative indications have been assigned as follows. Purification methods like boiling, household UF, RO and FO which are either energy intensive (electricity or firewood) or incorporate advanced systems and resources for short-term needs or have high rejection rates are assigned 1 out of 3. SODIS, solar distillation, BSF and household ceramic filter have been assigned 3 marks (out of 3) because they are either made from locally available materials with limited application of chemicals and are less dependent on non-renewable energy. Chlorination, combined flocculation–disinfection, UV and bicycle-operated UF have been classified with 2 marks (out of 3) due to their dependence either on chemical usage or due to the incorporation of exhaustible purifier components which cannot be locally sourced because of the use of sophisticated technology. Environmental sustainability has been accorded a priority of 2 out of 6 (Table  1 ).

Supply chain requirement

The selected areas of study are quite remote, wherein supply chain needs to be worked out from the nearby cities to nearby prominent villages/towns. Even if the water purifier is deployed once, unless the replacements and accessories are made available, the usage of purifiers in the long run may come to an end. Since supply chain is gradually improving, it has been assigned a priority of 2 out of 6 (Table  1 ). Biosand filters are assigned a score of 3 (out of 3) due to non-requirement of replaceables. Boiling, solar-based techniques, UV, ceramic filters, UF and RO need occasional supply in the form of fuel or replacement of a few accessories; hence, these have been given a score of 2 (out of 3). However, chlorination and FO-based techniques need strong supply chain network due to requirement of frequent replenishment and are given a score of 1 (out of 3).

Concluding remarks

This study adopts both academic and practical approaches towards water purifiers. The classification and description of water treatment alternatives are based on the operating technologies adopted for purification, so as to present a broad spectrum of possibilities. However, the review is based on the practical approach of evaluating water purifiers in the manner they can be used in the selected context. As presented in the review, there are a lot of alternatives available for a family-level water treatment even for a low-income household with decentralised water source in a developing country. The selection process of the optimal type of purifier for a given setting requires an assessment of different purification methods against several relevant attributes. However, the conditions in different places within a diverse country could be different. Based on the observations in the coastal region of Maharashtra in India, the attributes have been prioritised. The purifiers are then compared based on data available from primary and secondary sources. The review as an example indicates some of the purifiers suitable to the chosen scenario. Going further, this methodology can be used as a template to identify the best possible water purification technique relevant to the given scenario by tweaking the priority assigned to each attribute in the review based on the circumstance.

The viewpoint of this review was to classify, describe and review various household point-of-use water purifier based on prioritised attributes according to a local context. Some of the observations made through this review is as follows.

This is a wide spectrum of alternatives available in terms of technologies and water purifying devices.

Nowadays, membrane-based technologies in the realm of physical removal methods have a widespread adoption.

Based on the review, it can be inferred that no single purifier meets the mark in terms of all the attributes.

However, considering the summation of the product of the scores of the purifiers (> 90), it can be observed that boiling, biosand, ceramic and chlorination-based techniques seem to score the highest considering the priorities.

The above inference tends to match with the field observations in the selected villages, wherein these purifiers were used or deployed or seem agreeable to the people of the villages.

Based on field observation, it has been found that purifiers with low energy demands, those which are easy-to-use and handle and which can cater to flexible quantum of water requirements tend to have a higher adoption.

No matter what purification techniques are considered, certain attributes like purification performance will always be an important parameter for consideration.

It could probably be generalised that it would be hard to find a single water purifier which meets all the requirements as per all attributes in all contexts. Therefore, considering the specific needs and circumstances of the prevailing context, an optimum purifier could to be selected considering its advantages and limitations.

There is a huge scope for working on further fine-tuning low-cost, environmentally sustainable, easy-to-use water purifiers offering effective water treatment.

Point-of-use purifiers are especially suitable for water sourced from decentralised sources like tube wells, open wells, ponds and rain water harvesting tanks. It is observed that point-of-use purifiers are being increasingly used in developing countries irrespective of the water quality supplied by public utilities. This is so, because there is a high chance of contamination of water which is supplied even through centralised systems in areas like congested areas. PoU purifiers are also suitable for deployment during emergencies. Another observation noted is that most purifiers incorporate integrated treatment combing multiple purification methods, as generally observed in the case of household RO purifiers which generally incorporate micro-/nanofiltration and UV treatment.

It is, however, observed that household RO water purifiers are used as a common remedy for any type of water treatment need. RO purifiers are not only expensive and environmentally unsustainable (due to huge energy consumption and large release of discharge water) but may not be considered advisable for regular consumption (in case of routine water issues which are not very serious). It is in such a scenario that this review comes in hand, wherein the appropriate water purifier suitable to the relevant issue of water quality can be selected.

The future scope of this work could involve deeper market survey to consider more recent actual prices (apart from literature references) as these keep changing rapidly. Considering user perspective through surveys could also help in understanding the perceptions in terms of ease of use and sociocultural acceptability of the purifiers. This study does not include the ability of water purifiers to treat special chemical contaminants like arsenic, fluoride, etc.

This study considers an independent methodology for review of water purifiers based on references primarily from Peter-Varbanets et al. ( 2009 ) and Loo et al. ( 2012 ). However, there is further scope for undertaking a review based on a simpler way of integration of attributes could be as proposed in Pagsuyoin et al. ( 2015 ), which takes into account most of the attributes considered in this review.

Selecting a particular purifier depends on the several factors, among which some are changing needs, context of usage, development of technology, ease of use and market reach, etc. Amidst so many variables, identifying the appropriate purifier, is a challenge. However, as an example from this review, one can adopt a general methodology which could be used to identify the suitable water purifier for a given context. As described in earlier sections, the selection process first involves assigning the relevant priority to each attribute considering the prevailing situations in the given context. Secondly, rating all the water purifiers could possibly be adopted in the given context against each parameter. Finally, calculating the product of the score and the priority of the corresponding attribute identify the total score for each purifier. The appropriate water purifier is the one which has the highest score when calculated according this template.

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Acknowledgements

This work was carried out as part of a seminar coursework in IIT Bombay. The authors are grateful to the academic resources received from IIT Bombay, which contributed to most of this work. The authors also acknowledge the financial support of Tata Centre for Technology and Design (TCTD) for the project on Development of Clay based Water Purifier considering Local Needs, Skills and Materials , whose component was this study.

This study was conducted as part of a project supported by the Tata Centre for Technology and Design, Indian Institute of Technology Bombay.

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Venkatesha, R., Rao, A.B. & Kedare, S.B. Appropriate household point-of-use water purifier selection template considering a rural case study in western India. Appl Water Sci 10 , 124 (2020). https://doi.org/10.1007/s13201-020-01207-1

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DOI : https://doi.org/10.1007/s13201-020-01207-1

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Reverse Osmosis Literature Review

• 1.1 Google Scholar
• 2 Reverse Osmosis
• 3 Importance of Reverse Osmosis
• 4.1 A Review on Reverse Osmosis and Nanofiltration Membranes for Water Purification
• 4.2 Nanoparticles in reverse osmosis membranes for desalination: A state of the art review
• 4.3 Desalination Technologies for Developing Countries: A Review
• 4.4 Sustainable seawater reverse osmosis (SWRO) system design for rural areas of developing countries
• 4.5 Engineering antifouling reverse osmosis membranes: a review
• 4.6 Reverse osmosis technology for water treatment: State of the art review
• 4.7 Reverse osmosis membrane fabrication and modification technologies and future trends: a review
• 4.8 The challenges of reverse osmosis desalination: solutions in Jordan
• 4.9 Reverse Osmosis Water Purification by Cycling Action
• 4.10 Field evaluation of a community scale solar powered water purification technology: A case study of a remote Mexican community application
• 4.11 Purification of Contaminated Water with Reverse Osmosis: Effective Solution of Providing Clean Water for Human Needs in Developing Countries
• 5.1 DIY Maple Sap Reverse Osmosis (RO) Unit
• 5.2 DIY Reverse Osmosis For Home Drinking Water by Isopure Water
• 5.3 Build Your Own Reverse Osmosis System for Maple Syrup
• 5.4 How to Make an RO Water Filter at Home
• 5.5 Development and Filtration Performance of Polylactic Acid Meltblowns
• 6.1 Fundamentals of Membranes for Water Treatment
• 6.2 Tubular Membranes
• 6.3 A review of polymeric membranes and processes for potable water reuse
• 7.1 A critical overview of household slow sand filters for water treatment
• 8 Components
• 9 What Contaminants do Reverse Osmosis Systems Remove?
• 10 There are generally four stages in the Reverse Osmosis Process
• 11 Some factors that may affect the performance of a Reverse Osmosis System
• 12 References

Search Terms [ edit | edit source ]

Google scholar [ edit | edit source ].

• "reverse osmosis" membrane
• reverse osmosis "drinking water" international
• reverse osmosis "international development" OR "developing countries"
• drinking water treatment "reverse osmosis"

Reverse Osmosis [ edit | edit source ]

From Wikipedia: " Reverse osmosis ( RO ) is a water purification process that uses a partially permeable membrane to separate ions, unwanted molecules and larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic pressure, a colligative property that is driven by chemical potential differences of the solvent, a thermodynamic parameter."

Importance of Reverse Osmosis [ edit | edit source ]

RO is used to purify water by extracting particles of up to 0.0001 microns, the most powerful system for membrane purification. Completely removes dissolved salts in addition to everything said above. Using membrane technology can have many benefits such as:

• Allows to remove most of the solids (inorganic or organic) dissolved in the water (up to 99%).
• Removes suspended materials and microorganisms.
• Performs the purification process in a single stage and continuously.
• It is an extremely simple technology that does not require much maintenance and can be operated by non-specialized personnel.
• The process is carried out without phase change, with the consequent energy saving.
• It is modular and requires little space, which gives it exceptional versatility in terms of plant size: from 1 m3/day to 1,000,000 m3/day.
• Treatment of municipal and industrial effluents for pollution control and/or recovery of valuable reusable compounds.

Literature [ edit | edit source ]

A review on reverse osmosis and nanofiltration membranes for water purification [ edit | edit source ].

Yang, Zi, Yi Zhou, Zhiyuan Feng, Xiaobo Rui, Tong Zhang, and Zhien Zhang. 2019. "A Review on Reverse Osmosis and Nanofiltration Membranes for Water Purification" Polymers 11, no. 8: 1252. https://doi.org/10.3390/polym11081252

Abstract: "Sustainable and affordable supply of clean, safe, and adequate water is one of the most challenging issues facing the world. Membrane separation technology is one of the most cost-effective and widely applied technologies for water purification. Polymeric membranes such as cellulose-based (CA) membranes and thin-film composite (TFC) membranes have dominated the industry since 1980. Although further development of polymeric membranes for better performance is laborious, the research findings and sustained progress in inorganic membrane development have grown fast and solve some remaining problems. In addition to conventional ceramic metal oxide membranes, membranes prepared by graphene oxide (GO), carbon nanotubes (CNTs), and mixed matrix materials (MMMs) have attracted enormous attention due to their desirable properties such as tunable pore structure, excellent chemical, mechanical, and thermal tolerance, good salt rejection and/or high water permeability. This review provides insight into synthesis approaches and structural properties of recent reverse osmosis (RO) and nanofiltration (NF) membranes which are used to retain dissolved species such as heavy metals, electrolytes, and inorganic salts in various aqueous solutions. A specific focus has been placed on introducing and comparing water purification performance of different classes of polymeric and ceramic membranes in related water treatment industries. Furthermore, the development challenges and research opportunities of organic and inorganic membranes are discussed and the further perspectives are analyzed."

• Usage of inorganic and ceramic membranes
• Nanotechnology development for nanofiltration process
• Tunable pore structure
• Excellent mechanical and thermal tolerance
• Challenges in the future for the application of RO technology

Nanoparticles in reverse osmosis membranes for desalination: A state of the art review [ edit | edit source ]

Haleema Saleem, Syed Javaid Zaidi, Nanoparticles in reverse osmosis membranes for desalination: A state of the art review ,Desalination,Volume 475,2020,114171,ISSN 0011-9164, https://doi.org/10.1016/j.desal.2019.114171.

Abstract: The development of thin-film nanocomposite (TFNC) membranes utilizing nanoparticles present remarkable opportunity in the desalination industry. This review offers a comprehensive and in-depth analysis of TFNC membranes for reverse osmosis (RO) desalination by focusing on different issues existing in the RO process. Recent researches on nanoparticle incorporated TFNC membranes for application in water purification have been critically analyzed. The widely tested nanoparticles in these researches include carbon-based (carbon nanotube, graphene-oxide), metal and metal oxides-based (silver, copper, titanium dioxide, zinc oxide, alumina and metal-organic frameworks), and other nano-sized fillers like silica, halloysite, zeolite and cellulose-nanocrystals based. These nanoparticles demonstrated pronounced effect in terms of water flux, salt rejection, chlorine resistance, and anti-fouling properties of TFNC membranes relative to the typical thin-film composite (TFC) membranes. Here, we also focus on the environmental impact, commercialization, and future scope of TFNC membranes. From the current review, it is evident that the nanomaterials possess exclusive properties, which can contribute to the advancement of high-tech nanocomposite membranes with improved capabilities for desalination. Despite all the developments, there still exist significant difficulties in the large-scale production of these membranes. Hence, additional studies in this field are required to produce TFNC membrane with increased performance for commercial application.

• Review of recently developed TFNC RO membranes for desalination
• Improvement in the properties of TFNC membrane due to beneficial effect of nanoparticle
• Challenges associated with TFNC membranes and methods to overcome these
• Environmental impact of nanomaterials and their TFNC membranes
• Future prospects for advancement of TFNC membranes and their commercialization

Desalination Technologies for Developing Countries: A Review [ edit | edit source ]

Islam, M. S., Sultana, A., Saadat, A. H. M., Islam, M. S., Shammi, M., & Uddin, M. K. (2018). Desalination Technologies for Developing Countries: A Review. Journal of Scientific Research , 10 (1), 77–97. https://doi.org/10.3329/jsr.v10i1.33179

Abstract: Fresh water is rapidly being exhausted due to natural and anthropogenic activities. The more and more interest is being paid to desalination of seawater and brackish water in order to provide fresh water. The suitability of these desalination technologies is based on several criteria including the level of feed water quality, source of energy, removal efficiency, energy requirement etc. In this paper, we presented a review of different desalination methods, a comparative study between different desalination methods, with emphasis on technologies and economics. The real problem in these technologies is the optimum economic design and evaluation of the combined plants in order to be economically viable for the developing countries. Distillation plants normally have higher energy requirements and unit capital cost than membrane plants and produces huge waste heat. Corrosion, scaling and fouling problems are more serious in thermal processes compare to the membrane processes. On the other hand, membrane processes required pretreatment of the feed water in order to remove particulates so that the membranes last longer. With the continuing advancement to reduce the total energy consumption and lower the cost of water production, membrane processes are becoming the technology of choice for desalination in developing countries.

• Comparison of different desalination technologies.
• Low energy requirements and brackish water treatment are most common in developing countries.
• Unit capital cost and damage caused by corrosion or fouling are unusual in RO process.
• Pre-treatment of intake water is required in RO.

Sustainable seawater reverse osmosis (SWRO) system design for rural areas of developing countries [ edit | edit source ]

van Asselt, J., & de Vos, I. W. (2021). Sustainable seawater reverse osmosis (SWRO) system design for rural areas of developing countrie s .

• Solar-powered system, Kuwait
• Physical membrane types pros and cons: plate/frame, tubular, spiral, hollow
• Pretreatment types pros and cons: sand, cartridge, micro, ultra, nano (lists pore sizes)
• Debated: Open seawater vs. subsurface seawater intake

Engineering antifouling reverse osmosis membranes: a review [ edit | edit source ]

Zhao, S., Liao, Z., Fane, A., Li, J., Tang, C., Zheng, C., Lin, J., & Kong, L. (2021). Engineering antifouling reverse osmosis membranes: A review . Desalination , 499 , 114857. https://doi.org/10.1016/j.desal.2020.114857

Abstract: "Over the past decades, water scarcity and security have significantly stimulated the advances of reverse osmosis (RO) technology, which dominates the global desalination market. However, deterioration of membrane separation performance caused by inevitable fouling, including organic fouling, inorganic fouling, colloidal fouling and biofouling, calls for improved RO membranes with more durable antifouling properties. In this review, we analyze the correlations between membrane properties (e.g. surface chemistry, morphology, hydrophilicity, and charge) to antifouling performance. We evaluate the three key strategies for engineering fouling resistant thin film composite RO membranes, namely: (1) substrate modification before interfacial polymerization, (2) incorporating (hydrophilic/biocidal/antifouling) additives into the selective layer during interfacial polymerization, and (3) post (surface) modification after interfacial polymerization. Finally, we offer some insights and future outlooks on the strategies for engineering next generation of high performance RO membranes with durable fouling resistance. This review provides a comprehensive, state-of-the-art assessment of the previous efforts and strategies as well as future research directions for engineering antifouling RO membranes."

• Different membranes pros and cons
• Membranes get fouled: organic, inorganic, bio (most problematic), and colloidal
• Improve by being hydrophilic, neg. charge, smooth

Reverse osmosis technology for water treatment: State of the art review [ edit | edit source ]

Lilian Malaeb, George M. Ayoub, Reverse osmosis technology for water treatment: State of the art review , Desalination,Volume 267, Issue 1,2011,Pages 1-8,ISSN0011-9164,https://doi.org/10.1016/j.desal.2010.09.001

Abstract: This paper presents a review of recent advances in reverse osmosis technology as related to the major issues of concern in this rapidly growing desalination method. These issues include membrane fouling studies and control techniques, membrane characterization methods as well as applications to different water types and constituents present in the feed water. A summary of the major advances in RO performance and mechanism modeling is also presented and available transport models are introduced. Moreover, the two important issues of RO brine discharge and energy costs and recovery methods are discussed. Finally, future research trends and needs relevant to RO are highlighted.

• Research areas include brine discharge, fouling and removal of specific compounds.
• Modeling is important for better membrane characterization and for plant reliability.
• Existing cost assessment methodologies are not sufficiently accurate.
• Developing less energy-intensive systems is a main concern.
• Using new membrane materials is also a subject of future research.

Reverse osmosis membrane fabrication and modification technologies and future trends: a review [ edit | edit source ]

Hailemariam, R. H., Woo, Y. C., Damtie, M. M., Kim, B. C., Park, K.-D., & Choi, J.-S. (2020). Reverse osmosis membrane fabrication and modification technologies and future trends: A review. Advances in Colloid and Interface Science , 276 , 102100. https://doi.org/10.1016/j.cis.2019.102100

Abstract: "Reverse osmosis (RO) is the most widely used technology in water treatment and desalination technologies for potable water production. Since its invention, RO has undergone significant developments in terms of material science, process, system optimization, methods of membrane synthesis, and modifications. Among various materials used for the synthesis of an RO membrane, the polyamide thin-film composite (PA-TFC) is by far the most common, owing to its excellent water permeability high salt rejection, and stability. However, a tradeoff between membrane permeability and salt rejection and membrane fouling has been a major hindrance for the effective application of this membrane. Thus, a broad investigation has been carried out to address these problems, and among which co -solvent interfacial polymerization (CAIP) and the surface modification of substrates and active layers of RO membrane have been the most effective approaches for controlling and improving the surface properties of the PA-TFC membrane. In this review paper, the problems associated with the RO membrane processes and strategies has been discussed and addressed in detail. Furthermore, as the focus of this review, the major advancements in the strategies used for enhancement of RO membrane performance through CAIP, and surface modifications were scrutinized and summarized."

• Reverse osmosis steps
• Four steps in reverse osmosis plant: pre-treat for compatibility, pumping/pressure (overcome osmotic pressure), membrane separation, and post-treat
• Issues of reverse osmosis (+their solutions): membrane deterioration via fouling (smooth membrane, small neg. charge, high hydrophilicity), permeability/salt rejection, chlorination, boron extraction (run multiple times w/ pH balance), brine waste

The challenges of reverse osmosis desalination: solutions in Jordan [ edit | edit source ]

Maureen Walschot, Patricia Luis & Michel Liégeois (2020) The challenges of reverse osmosis desalination: solutions in Jordan , Water International, 45:2, 112-124, DOI: 10.1080/02508060.2020.1721191

Abstract: Desalinating water through reverse osmosis is becoming more economically affordable. Identifying the challenges in adopting desalination technology may help countries address water security concerns. In this article, we examine these challenges and present some of the solutions implemented in the Kingdom of Jordan, such as the creation of a cooperative water project to reduce financial investment and transportation costs and the coupling of renewable energy to desalination technology. Reverse osmosis desalination can play a role in promoting regional cooperation.

• Type of feed water (seawater or brackish)
• Energy source depending of the local availability and the cost of an energy source
• Plant size (most high and medium-income countries can afford large-scale desalination technology)
• Brine disposal to water bodies as the sea or open spaces
• CO2 emissions of, at least, 20%
• Energy consumption for its operation

Reverse Osmosis Water Purification by Cycling Action [ edit | edit source ]

Ravi V.K., Sushmitha V., Kumar M.V.P.., and Thomas A. (2017). Reverse Osmosis Water Purification by Cycling Action . International Journal of Latest Engineering Research and Applications , 2 (5), 54-59.

Abstract: "Pure water is very much essential to survive, but now a days the water is getting contaminated due to Industrialisation which leads to many water-releated diseases. Reverse Osmosis(RO) Water Purification by Cycling Action meets the needs of people without requiring any electrical energy. RO is a physical process that uses the osmosis phenomenon, that is, the osmotic pressure difference between the salt water and the pure water to remove the salts from water. Water will pass through the membrane, when the applied pressure is higher than the osmotic pressure, while salt is retained. As a result, a low salt concentration permeate stream is obtained and a concentrated brine remains at the feed side. A typical RO system consists of four major subsystem: pre-treatment system, high-pressure pump, membrane module and post treatment system. In operation by pedaling the cycle, man power is converted into mechanical energy which is further converted into hydraulic energy in RO pump."

• Human powered (electricity free) reverse osmosis
• "4 Stage = Sediment + Pre-Carbon + RO Membrane + Post-Carbon"
• Collect water, cycle, and clean when home

Field evaluation of a community scale solar powered water purification technology: A case study of a remote Mexican community application [ edit | edit source ]

Elasaad, H., Bilton, A., Kelley, L., Duayhe, O., & Dubowsky, S. (2015). Field evaluation of a community scale solar powered water purification technology: A case study of a remote Mexican community application . Desalination , 375 , 71–80. https://doi.org/10.1016/j.desal.2015.08.001

Abstract: "Lack of clean water in small remote communities in the developing world is a major health problem. Water purification and desalination systems powered by solar energy, such as photovoltaic powered reverse osmosis systems (PVRO), are potential solutions to the clean water problems in these small communities. PVRO systems have been proposed for various locations. However, small PVRO systems with production on the order of 1 m3/day for remote communities present some unique technical, cost and operational problems. This paper reports on a project in which a PVRO system is designed, fabricated and deployed in remote village in the Yucatan Peninsula of Mexico. The community residents are indigenous people who are subsistence farmers and beekeepers. Technical and economic models used to configure the system for the community are presented. A plan is developed in cooperation with the community aimed at making the system self-sustaining in the long term. Methods and materials are developed to permit the community members to operate and maintain the system themselves. The results provide insights for the design and deployment of small community-scale PVRO systems in remote communities."

• Photovoltaic reverse osmosis system for drinking water
• Issues with system: cost of shipping parts, language differences for training, hands-on training needed, water source quality
• Physical parts in reverse osmosis system (solar panel, membrane, filters, pump, testing, electronics, batteries, UV lamps) and diagram of process shown
• Cost: $10,000 USD to start and $1,342 USD annually

Purification of Contaminated Water with Reverse Osmosis: Effective Solution of Providing Clean Water for Human Needs in Developing Countries [ edit | edit source ]

Wimalawansa, S. J. (2013). Purification of Contaminated Water with Reverse Osmosis: Effective Solution of Providing Clean Water for Human Needs in Developing Countries. International Journal of Emerging Technology and Advanced Engineering, 3 (12).

Abstract: "Approximately 25% of the world's population has no access to clean and safe drinking water. Even though freshwater is available in most parts of the world, many of these water sources contaminated by natural means or through human activity. In addition to human consumption, industries need clean water for product development and machinery operation. With the population boom and industry expansion, the demand for potable water is ever increasing, and freshwater supplies are being contaminated and scarce. In addition to human migrations, water contamination in modern farming societies is predominantly attributable to anthropogenic causes, such as the overutilization of subsidized agrochemicals―artificial chemical fertilizers, pesticides, fungicides, and herbicides. The use of such artificial chemicals continue to contaminate many of the precious water resources worldwide. In addition, other areas where the groundwater contaminated with fluorides, arsenic, and radioactive material occur naturally in the soil. Although the human body is able to detoxify and excrete toxic chemicals, once the inherent natural capacity exceeded, the liver or kidneys, or both organs may fail. Following continual consumption of polluted water, when the conditions are unfavourable and the body's thresholds are exceeded, depending on the type of pollutants and toxin, liver, cardiac, brain, or renal failure may occur. Thus, clean and safe water provided at an affordable price is not only increasingly recognized, but also a human right and exceedingly important. Most of the household filters and methods used for water purification remove only the particulate matter. The traditional methods, including domestic water filters and even some of the newer methods such as ultra-filtration, do not remove most of the heavy metals or toxic chemicals from water than can harm humans. The latter is achieved with the use of reverse osmosis technology and ion exchange methods. Properly designed reverse osmosis methods remove more than 95% of all potential toxic contaminants in a one-step process. This review explains the reverse osmosis method in simple terms and summarizes the usefulness of this technology in specific situations in developing countries."

• Spiral-wound membrane shape + nanometer pore size for reverse osmosis
• Why RO > other filtering methods
• Physical parts in reverse osmosis system and process (including different options for each step)
• Lowered contaminant removal via fouling (backwashing helps).

DIY [ edit | edit source ]

Diy maple sap reverse osmosis (ro) unit [ edit | edit source ].

rsook74. DIY Maple Sap Reverse Osmosis (RO) Unit . Instructables. https://www.instructables.com/DIY-Maple-Sap-Reverse-Osmosis-RO-Unit/

• Physical parts needed

DIY Reverse Osmosis For Home Drinking Water by Isopure Water [ edit | edit source ]

Isopure Water . DIY Reverse Osmosis System for Home Drinking Water by Isopure Water . (2020, December 12). Isopure Water. https://www.isopurewater.com/blogs/news/diy-reverse-osmosis-system

• Cost: max $150 for parts + annual filters

Build Your Own Reverse Osmosis System for Maple Syrup [ edit | edit source ]

Michelle. (2019, January 8). Build your own Reverse Osmosis system for maple syrup . Souly Rested.https://soulyrested.com/2019/01/08/build-your-own-reverse-osmosis-system-for-maple-syrup/

• Cost: roughly $300-$350

How to Make an RO Water Filter at Home [ edit | edit source ]

Derek. (2017, June 20). How to Make a Reverse Osmosis Water Filter at Home . best-ro-system.com. https://www.best-ro-system.com/make-your-own-water-filter/

Development and Filtration Performance of Polylactic Acid Meltblowns [ edit | edit source ]

Liu, Y., Cheng, B. and Cheng, G., 2010. Development and filtration performance of polylactic acid meltblowns. Textile research journal, 80(9), pp.771-779. https://doi.org/10.1177/0040517509348332

Polylactic acid (PLA) is a biodegradable material that can be used to make meltblowns (MBs, which are fabrics made by the meltblowing method) using direct melt spun. PLA MBs were successfully produced in a 20 cm laboratory meltblown line. The relationships between the processing parameters and the filtration performance of PLA MBs were explored in this study. The key parameters regarding the filtration performance of PLA MBs, including the PLA chip drying process, the melt temperature, the hot air temperature, and the width of the air gap, were thoroughly investigated using scanning electronic microscopy, filtration efficiency, and breathability tests. It was found that the processing parameters were significant to the structure, thus the filtration performance of PLA MBs. PLA turned out to be a favorable material for meltblowing. The preferred spinning temperature was 220°C for optimal web quality. The diameter of PLA MB fibers became larger with the increase of hot air temperature. With the increase of air gap width, the diameter of PLA MB fibers went up, whereas the crimp level went down. This information may be useful for the future development of a commercialized production line of PLA MBs.

• basic schematics of MB system and spinning die; could base on recyclebot and winding system

Fabricating RO Membranes [ edit | edit source ]

The production is divided into the following process stages:

• Mechanical conditioning of the pulp: The pulp is fibrillated by different types of crushers, such as hammer mills and disc refiners, where the successive arrangement of both types of crushers ensures optimal dissolution.
• Chemical pretreatment: The fibrillated cellulose is treated with acetic acid with moderate agitation at 25°C to 50°C for approximately 1 h, resulting in continuous evaporation and condensation of the acetic acid in the spaces between the fiber particles. In addition to this acetic acid steam pretreatment, there is also a fine pulp state pretreatment. In this process, the cellulose is introduced in large quantities of water or diluted acetic acid and is vigorously stirred. Subsequent process steps, such as pressing or centrifugation, constantly increase the concentration of cellulose in the pulp.
• Cellulose Acetylation: In the commercial production of cellulose acetates, the acetic acid process or the methylene chloride process is often used for acetylation. In acetic acid processes, the pretreated cellulose mass is reacted in an acetylation mixture of acetic acid solvent with excess acetic anhydride, which serves as esterification agent, and with sulfuric acid as catalyst under vigorous mechanical mixing. In the methylene chloride process, methylene chloride is used in the acetylation mixture as a solvent instead of acetic acid. Since low boiling methylene chloride can be easily removed by distillation, process control is achieved even with highly viscous solutions. Even at low temperatures, it can dissolve cellulose triacetate very well. A small amount of sulfuric acid can be used as a catalyst, but often perchloric acid as well.
• Partial Hydrolysis: To obtain the desired secondary cellulose acetate types, cellulose triacetate is obtained by hydrolysis. For this purpose, the triacetate solution is typically heated to 60-80°C in the presence of an acid catalyst (usually sulfuric acid) by adding water while stirring and heating. Hydrolysis is controlled by the concentration of sulfuric acid, the amount of water and the temperature in such a way that the desired molecular degradation is achieved. The hydrolysis process is then stopped by adding basic salts that neutralize the acid catalyst.
• Cellulose acetate precipitation: When precipitating cellulose acetate from the reaction solution using dilute acetic acid, it is important to obtain uniform and easily washable cellulose acetate flakes. Before precipitation, any methylene chloride present must be completely removed by distillation. Acetic acid is then recovered.
• Washing and drying: By means of intensive washing, which is usually carried out against the current, the acetic acid must be removed from the flakes down to the smallest traces, otherwise damage ("charring") will occur during the drying process. After pressing the washing liquid, the flakes are dried in a conveyor dryer through which hot air flows to a residual moisture content of approx. 2-5%. For the further production of very high-quality, thermally stable, brightly colored and color-stable thermoplastic molding compounds, the cellulose acetate flakes are also bleached and stabilized in additional process steps before final drying.
• Flake Mixing: Before transporting the cellulose acetate flakes to a collection container from where they are transported to the appropriate processing plants, the flakes are mixed in a precisely controlled manner. This is to compensate for deviations of the cellulose acetates from different production batches. [1]

Fundamentals of Membranes for Water Treatment [ edit | edit source ]

Sagle, A. and Freeman, B., 2004. Fundamentals of membranes for water treatment. The future of desalination in Texas, 2(363), p.137. https://texaswater.tamu.edu/readings/desal/membranetechnology.pdf

• Good intro to the tech
• Commercial cellulose acetate (CA) membranes used for reverse osmosis have a degree of acetylation of about 2.7

Tubular Membranes [ edit | edit source ]

Daicen Membrane-Systems Ltd. (n.d.). Tubular Type Module . Tubular type module. Retrieved September 22, 2021, from https://daicen.com/en/products/membrane/chube.html .

• Treats human waste
• Specs for membrane (# of tubes, inner diameter, area)

PCI Membranes Filtration Group. (2021, August 25). C10 Series Tubular Membrane Modules . PCI Membranes. https://www.pcimembranes.com/products/c10-series-tubular-membrane-modules/

• Data Sheet: Components of a tubular membrane (ex. O Ring)

A review of polymeric membranes and processes for potable water reuse [ edit | edit source ]

David M. Warsinger, Sudip Chakraborty, Emily W. Tow, Megan H. Plumlee, Christopher Bellona, Savvina Loutatidou, Leila Karimi, Anne M. Mikelonis, Andrea Achilli, Abbas Ghassemi, Lokesh P. Padhye, Shane A. Snyder, Stefano Curcio, Chad D. Vecitis, Hassan A. Arafat, John H. Lienhard. (2018). A review of polymeric membranes and processes for potable water reuse , Progress in Polymer Science , Volume 81, Pages 209-237, SSN 0079-6700. https://doi.org/10.1016/j.progpolymsci.2018.01.004.

Abstract: Conventional water resources in many regions are insufficient to meet the water needs of growing populations, thus reuse is gaining acceptance as a method of water supply augmentation. Recent advancements in membrane technology have allowed for the reclamation of municipal wastewater for the production of drinking water, i.e., potable reuse. Although public perception can be a challenge, potable reuse is often the least energy-intensive method of providing additional drinking water to water stressed regions. A variety of membranes have been developed that can remove water contaminants ranging from particles and pathogens to dissolved organic compounds and salts. Typically, potable reuse treatment plants use polymeric membranes for microfiltration or ultrafiltration in conjunction with reverse osmosis and, in some cases, nanofiltration. Membrane properties, including pore size, wettability, surface charge, roughness, thermal resistance, chemical stability, permeability, thickness and mechanical strength, vary between membranes and applications. Advancements in membrane technology including new membrane materials, coatings, and manufacturing methods, as well as emerging membrane processes such as membrane bioreactors, electrodialysis, and forward osmosis have been developed to improve selectivity, energy consumption, fouling resistance, and/or capital cost. The purpose of this review is to provide a comprehensive summary of the role of polymeric membranes and process components in the treatment of wastewater to potable water quality and to highlight recent advancements and needs in separation processes. Beyond membranes themselves, this review covers the background and history of potable reuse, and commonly used potable reuse process chains, pretreatment steps, and advanced oxidation processes. Key trends in membrane technology include novel configurations, materials, and fouling prevention techniques. Challenges still facing membrane-based potable reuse applications, including chemical and biological contaminant removal, membrane fouling, and public perception, are highlighted as areas in need of further research and development.

Pre-filters [ edit | edit source ]

A critical overview of household slow sand filters for water treatment [ edit | edit source ].

B.L.S. Freitas, U.C. Terin, N.M.N. Fava, P.M.F. Maciel, L.A.T. Garcia, R.C. Medeiros, M. Oliveira, P. Fernandez-Ibañez, J.A. Byrne, L.P. Sabogal-Paz, A critical overview of household slow sand filters for water treatment ,Water Research,Volume 208,2022,117870,ISSN 0043-1354,https://doi.org/10.1016/j.watres.2021.117870.

Abstract: Household, or point-of-use (POU), water treatments are effective alternatives to provide safe drinking water in locations isolated from a water treatment and distribution network. The household slow sand filter (HSSF) is amongst the most effective and promising POU alternatives available today. Since the development of the patented biosand filter in the early 1990s, the HSSF has undergone a number of modifications and adaptations to improve its performance, making it easier to operate and increase users' acceptability. Consequently, several HSSF models are currently available, including those with alternative designs and constant operation, in addition to the patented ones. In this scenario, the present paper aims to provide a comprehensive overview from the earliest to the most recent publications on the HSSF design, operational parameters, removal mechanisms, efficiency, and field experiences. Based on a critical discussion, this paper will contribute to expanding the knowledge of HSSF in the peer-reviewed literature.

• Household slow sand filter is one of the most promising home scale treatments.
• HSSF is efficient in improving drinking water quality in isolated communities.
• Modification in the HSSF design and operation may encourage research.
• There is a lack of literature on protozoa, cyanobacteria, and emerging pollutants.

Components [ edit | edit source ]

• Valve descriptions
• "These tubular membranes were 250 mm in length with internal diameter of 7 mm."
• Pore size for ultra, micro, and nano filtration

What Contaminants do Reverse Osmosis Systems Remove? [ edit | edit source ]

Public water suppliers work hard to provide clean water for their customers. The problem is that there are many contaminants, especially those that cause taste and odor issues, which are simply not EPA regulated. These contaminants can easily penetrate aquifers, streams and rivers, bringing impurities straight to your water lines.

That's where Reverse Osmosis comes in. With a Reverse Osmosis filtration system, you can filter out impurities and produce outstanding drinking water for your home or business.

How Much Of A Contaminant Can A Reverse Osmosis System Remove?

• Fluoride (85-92%)
• Lead (95-98%)
• Chlorine (98%)
• Pesticides (up to 99%)
• Nitrates (60-75%)
• Sulfate (96-98%)
• Calcium (94-98%)
• Phosphate (96-98%)
• Arsenic (92-96%)
• Nickel (96-98%)
• Mercury (95-98%)
• Sodium (85-94%)
• Barium (95-98%

There are generally four stages in the Reverse Osmosis Process [ edit | edit source ]

SEDIMENT FILTER: This pre-filter stage is designed to strain out sediment, silt, and dirt and is especially important as the sediment filter protects dirt from getting to the delicate RO membranes that can be damaged by sediment. Learn more about sediment filter.

CARBON FILTER: The carbon filter is designed to remove chlorine and other contaminants that affect the performance and life of the RO membrane as well as improve the taste and odor of your water.

REVERSE OSMOSIS MEMBRANE: The semipermeable RO membrane in your RO system is designed to allow water through, but filter out almost all additional contaminants.

POLISHING FILTER: In a four-stage RO System, a final post filter (carbon filter) will "polish" off the water to remove any remaining taste and odor in the water. This final filter ensures you'll have outstanding drinking water.

Some factors that may affect the performance of a Reverse Osmosis System [ edit | edit source ]

• Incoming water pressure (most on municipal city tap water have 40-85 psi, but if water pressure is too low, RO system will not operate properly)
• Water Temperature (i.e. cold water takes longer to filter to filter)
• Type and number of total dissolved solids (TDS) in the tap water
• The quality of the filters and membranes used in the RO System (see operating specifications for your system)

References [ edit | edit source ]

Centers for Disease Control and Prevention. (2020, August 4). Technical information on Home Water Treatment Technologies . Centers for Disease Control and Prevention. Retrieved October 1, 2021, from https://www.cdc.gov/healthywater/drinking/home-water-treatment/household_water_treatment.html.

Michelle. (2019, January 8). Build your own Reverse Osmosis system for maple syrup . Souly Rested. https://soulyrested.com/2019/01/08/build-your-own-reverse-osmosis-system-for-maple-syrup/

Ravi V.K., Sushmitha V., Kumar M.V. P., and Thomas A. (2017). Reverse Osmosis Water Purification by Cycling Action . International Journal of Latest Engineering Research and Applications , 2 (5), 54-59.

Zhao, S., Liao, Z., Fane, A., Li, J., Tang, C., Zheng, C., Lin, J., & Kong, L. (2021). Engineering antifouling reverse osmosis membranes: A review. Desalination , 499 , 114857. https://doi.org/10.1016/j.desal.2020.114857

• ↑ https://en.wikipedia.org/wiki/Cellulose_acetate#Method
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• Pages with references but no references tag

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Site search, our 7 best reverse osmosis system picks (2024).

We may be compensated if you purchase through links on our website. Our Reviews Team is committed to delivering honest, objective, and independent reviews on home products and services.

Investing in and installing a reverse osmosis water filter gives you cleaner, more pure water by removing dirt, chemicals, microorganisms, heavy metals, and other contaminants and impurities. These systems can vary greatly in price, with budget-friendly models starting around $150 – $300 and higher-end systems running anywhere from $500 – $1,000.

Our team has reviewed some of the best reverse osmosis systems for your home to help you choose the right one for your home. Overall, our top pick is the Waterdrop G3P800 8-Stage Tankless RO System , which uses a nine-stage filtration system to eliminate over 100 harmful contaminants from your water. Read our guide below for more of our top picks.

Reverse Osmosis System Overall

Waterdrop G3P800 8-Stage Tankless RO System

Best Countertop Reverse Osmosis System

Aquatru 4-stage countertop ro system.

Best Drinking Water Filtration System

Apec water systems roes-50 5-stage ro system, top 7 reverse osmosis systems.

• Best Reverse Osmosis System Overall : Waterdrop G3P800 8-Stage Tankless RO System
• Best Countertop Reverse Osmosis System: AquaTru 4-Stage Countertop RO System
• Best Drinking Water Filtration System: APEC Water Systems ROES-50 5-Stage RO System
• Best Value: iSpring 6-Stage Reverse Osmosis System
• Best Undersink Reverse Osmosis System: Express Water RO5DX 5-Stage Under Sink RO System
• Best Budget Model: Whirlpool WHAROS5 RO Water Filtration System
• Most Compact: Ecoviva Countertop Reverse Osmosis System

Compare Top Reverse Osmosis Systems

Best Reverse Osmosis System Overall

Prices taken at time of publishing.

• $999 at Amazon

What Are People Saying About the Waterdrop G3P800 8-Stage Tankless RO System?

Customers praised this system’s effectiveness. Several customers purchased tap water testing kits to determine the efficiency of this system and found that the water it provided was comparable to filtered bottled water. However, we also saw that some customers found its faucet to be flimsy, and some said it was overly loud while in operation.

“The reverse osmosis system is a high-quality product. The installation process is extremely easy and quick, as any person can install the system due to the clear instructions manual. The filtered water tastes crisp, refreshing, and pure. It tastes no different from bottled water. I would recommend it to anyone who wants refreshing clean water. The customer service was very quick to respond and was extremely patient with my questions and responses.” — Guo L. Huang via Amazon

“Tankless system requires an internal pump, which has to run every time you open the faucet. And also in the middle of the night when it does its flushing process. Spec is 65 dB, but to make it simple, we can hear the downstairs system flushing in the middle of the night from our upstairs bedroom with the door closed. Our kitchen is open to our family room, where we watch TV – every time someone gets water, we have to pause the TV. Some are claiming the noise isn’t that bad – I don’t understand how unless the unit is in a pretty thick cabinet or somehow farther away from where the humans are.” — Jim via Amazon

• $469 at Amazon

What Are People Saying About the AquaTru 4-Stage Countertop RO System?

Customers we found said that this reverse osmosis system was strong enough to remove even solid particles from the gallons of water it filtered. However, customers who weren’t satisfied with their purchase complained that it stopped working after a short period of time, while others were disappointed in how often this filter needed to be refilled.

“I have purchased other big-name brand water filters. I was very disappointed in the taste of their filtered water-it tasted of minerals and just plain yucky, for lack of a better word. I’ve heard good things about the AquaTru filter and thought I’d give it a try. I just received it and put it together yesterday. The water is so pure and delicious! It was very easy to assemble and prime to get it going! It is well made and it looks beautiful on my kitchen counter. I love the convenience of having it right where I need water! I highly recommend this AquaTru water filter! You’ll love it.” — Janet Tope via Amazon

“I drink a lot of water during the day and the amount of filtered water in the pitcher only lasted one day before having to be refilled again. The design seemed inefficient in that a lot of ‘waste’ water had to be emptied each time, and everything cleaned daily with soap and water. Too much of a hassle.” — Susan P. via Amazon

• $199.95 at Amazon

What Are People Saying About the APEC Water Systems ROES-50 5-Stage RO System?

Reviews we found complimented the efficiency of this system, which multiple customers said saved them more energy and money than previous reverse osmosis systems they had used. However, some customers weren’t satisfied with the system’s installation process, which required a  cordless drill  to drill holes. Others found that it didn’t reduce their water level’s TDS by as much as they were hoping.

“I am submitting this review 3 months after installation. I couldn’t be happier with this system! I have a lot of iron in my well water, use a softener to remove most of the iron and harness. However, the water still has a slightly funny taste and is yellow from suspended iron. This system finished the job. Not only does my water taste good, it’s perfectly clear now. I am so pleased, that I took the time to run a line from this system to my ice maker in my refrigerator .” —Michigan Shopper via Amazon

“For whatever reason, this system did not work very well for me. I was mostly trying to reduce total dissolved solids in our well water for use with an ice maker. Our TDS value is about 67 from our well water. With the system installed, TDS was reduced, but only down to about ~42, so maybe a ~35% reduction. Not great, not terrible. We never had any taste/odor issues with our water, so I can’t comment on the efficacy of the carbon filters— the RO seems marginal at best though.” — Clay N. Cowgill via Amazon

iSpring 6-Stage Reverse Osmosis System

• $218.99 at Amazon

What Are People Saying About the iSpring 6-Stage Reverse Osmosis System?

Our team found that customers frequently complimented how easy to install this system was, with the process being easy enough for even those with no DIY experience to manage. Reviewers who rated this product poorly complained that the system’s parts leaked.

“Love this system! Super easy to install with video and easy instructions. Had extremely high nitrates (+20). After installation, nitrates were down to 7! Water tastes amazing. The only issue I had was with my new RO system faucet leaking. I contacted customer service via email and received a response…. Wow! I cant say enough about the service I received!”  — Stacy via Amazon

“I really want to like this product. Actually, I have bought it three times since the price is reasonable. However, 3 out of the 3 installations had something leaking. The first two times were an o-ring on one of the large filters. I used Vaseline as recommended, but for some reason, the o-ring area leaked. They fortunately provide spare o-rings (probably knowing this is a common issue) so I replaced the o-ring, re-installed and everything was just fine. So either their o-rings have some kind of quality issue, or their design does, but it looks like the design is a very commonly used design.” — Turbo97se via Amazon

Best Undersink Reverse Osmosis System

Express Water RO5DX 5-Stage Under Sink RO System

• $152.99 at Amazon

What Are People Saying About the Express Water RO5DX 5-Stage Under Sink RO System?

Our team noticed that customers praised this RO’s filter design because the swivel connections allowed for quick-change filters without removing any tubing. However, dissatisfied customers complained about the system’s maintenance process, which required regular intensive cleaning in addition to filter changes. Others felt the flavor of the water after it passed through this RO system still did not taste right.

“We live in Hawaii and usually had to fill up water jugs to get filtered water. No more! It’s an investment, but man, it is worth it! It does take a minute to install and figure out, so definitely dedicate some time to putting it together. We’ve had it for several months and no complaints. The water tastes great, and the tap works amazing. It looks sleek and clean as well. 10/10 recommend.” — Amazon Customer via Amazon

“The countertop osmosis filter didn’t meet my flavor expectations. Despite using it consistently for two weeks, it retains an unpleasant plastic aftertaste that doesn’t resemble refreshing, clean water. Additionally, the need to frequently refill the container due to the waste water occupying most of it is inconvenient. This results in having to fill both sides regularly, consuming a significant amount of water. Furthermore, the instructions for setting up the product are unclear.” — Julian Kwan via Amazon

Best Budget Model

Whirlpool WHAROS5 RO Water Filtration System

• $220.21 at Amazon

What Are People Saying About the Whirlpool WHAROS5 RO Water Filtration System?

We found that customers who were impressed with this product particularly liked that it was easy to install, made for great-tasting clean water, and that it produced quick results. On the other hand, we also saw some customers who felt that some of the parts were not high quality, and others felt as though it wasted too much water.

“I have well water at home, it’s very hard (>30gpg) and has fairly high TDS (500ppm), I run through a sediment filter (5micron) then a water softener, then for drinking water it goes though this RO filter. Immediately after installation the TDS went from 500 down to 60 (ppm). After running it for a few days the TDS dropped even further to about 26ppm — this was my expectation and I’m pleased with it’s performance. I will keep this system for as long as it keeps producing water of this quality.” — C. Farmer via Amazon

“RO system like this one is known to produce clean and waste water which is discharged to the drain. Filter-based filtration systems, on the other hand, don’t waste water. So I expected waste water, but I didn’t know it wastes so much water until I measured it. Since none of the documents specify the amount of wasted water, I decided to measure it and was surprised. To be fair, the quality and taste of the produced, clean water is great.” — hermits via Amazon

Most Compact

Ecoviva Countertop Reverse Osmosis System

• $230.25 at Amazon

Good for: Homeowners seeking a countertop model with a sleek design that will blend in with other kitchen appliances.

What Are People Saying About the Ecoviva Countertop Reverse Osmosis System?

Our team found that customers who gave this product a positive review liked that it had a compact design and that it worked quickly to filter water. Additionally, others were impressed that it was easy to use and significantly improved water taste. However, others found it laborious to have to empty the tank after each use, and others said it didn’t always fully fill the carafe. 

“This counter top water purifier is excellent. The water tastes so much better than my unfiltered tap water. I was surprised to see that my water quality is actually pretty good, but this device still made a significant difference in the taste, and there is no more chlorine smell or presence. It actually removes impurities in the water rather than just improving taste, like some gravity-fed pitcher filters.” — fire_lion via Amazon

“The product did not fill the carafe even if the tank was full. Tried it several times and it won’t work. I waited for two days and worked again, but on and off. The other frustrating issue is that it doesn’t have an off/on button, so you have to unplug it all the time to start. It doesn’t start if you leave it plugged. For me, it is not safe to be plugging and unplugging it.” — ML via Amazon

Buying Guide To Reverse Osmosis Systems

A reverse osmosis water filtration system is an easy form of water treatment. It works by removing contaminants from your tap water during the filtration process.

However, before deciding on which RO system works best for your home, there are several factors you should take time to consider to ensure you’re making the right purchase. First, you should examine the various types of reverse osmosis systems and determine if you want a countertop or sink reverse osmosis system.

From there, you can determine what water filters the system has and if it includes a storage tank or other area for keeping water. You can also consider factors such as the capacity of the system, the water pressure levels, and the amount of safety features.

How do you determine the right size for an RO system?

Reverse osmosis systems can vary greatly in size. Most models we examined are designed to be stored underneath a sink, although countertop versions also exist. Measure how much space you have under or around your sink before deciding whether you need a tankless reverse osmosis system or if you have room for something larger.

Do reverse osmosis systems have water tanks?

Some RO filtration systems have a tank that stores water before it’s transferred to your sink. Others forgo the tank to save space. The type you purchase should depend on how much space you have in your kitchen.

What are the different types of RO system filters?

Reverse osmosis systems have multiple stages of filtration, moving water through three to eight filters to remove contaminants. Common types of filters we found include:

• Sediment: This type of filter removes dirt and other large particles.
• Carbon: This type removes chlorine.
• Reverse osmosis: An RO membrane removes particles that are larger than water molecules.
• UV: This type of filter kills microorganisms.
• Targeted: These filters remove specific types of contaminants, such as nitrate or fluoride. They’re only needed if these contaminants are present in large quantities.
• Remineralization: This filter introduces calcium and magnesium into the purified water to balance its pH level.

How is the capacity of an RO system measured?

The amount of water that a reverse osmosis system can purify at one time, also called the flow rate, is typically measured in gallons per day, or GPD. Choose a capacity based on how much water you and your family use in a day. For example, if you live alone, a system that purifies four gallons of water will be enough. However, if you have a family of five, you will need a reverse osmosis system that can purify at least 20 gallons of water.

What safety features should you look for in a reverse osmosis system?

We’ve found that some reverse osmosis systems have built-in features to ensure that they run smoothly. Common features we noticed include leak detectors and replacement filter indicators.

How do you measure the water pressure of an RO system?

In order for a reverse osmosis water filter to work properly, our team found it should have at least 50 PSI. RO water filters with above an 80 PSI are ideal for homes where the water supply lacks pressure.

Learn more about the cost of reverse osmosis systems .

How To Install a Reverse Osmosis Filter

While you can always hire a professional to install a reverse osmosis filter in your home, passionate DIYers can also try it on their own if they have the right materials, including an adjustable wrench , pencil or marker, screwdriver , and drill .  

In the video below, This Old House ’s Richard Trethewey takes you through the step-by-step process of installing a reverse osmosis filter underneath a kitchen sink to remove impurities from your home’s water. 

What is an NSF Certification?

National Sanitation Foundation (NSF) is an independent, third-party certification organization that tests and certifies products and services to ensure they meet certain public health and safety standards.

When a water filter is NSF certified, it means that it has been tested and found to meet or exceed specific performance standards for the reduction of a variety of contaminants, such as lead, chlorine, bacteria, and other impurities. This can provide peace of mind to consumers, knowing that the filter they are using has been independently verified to be effective at removing potentially harmful substances from their drinking water.

Furthermore, many government agencies and organizations require NSF certification for water filters to ensure that they meet specific standards for public health and safety. For example, many states require NSF certification for water filters used in schools, hospitals, and other public facilities.

Frequently Asked Questions About Reverse Osmosis Systems

How does a reverse osmosis system work.

A reverse osmosis system removes dirt, bacteria, and chemicals from your drinking water. It does this by passing water through a series of filters that each target a specific contaminant. Since the filters are semipermeable membranes, they allow water to pass through them while trapping undesirable molecules. The resulting water is purer than standard tap water.

Why do I need a reverse osmosis system?

A reverse osmosis system can provide your whole house with healthier and better-tasting water. However, our team notes that it’s especially important to use a reverse osmosis system if you live in an area with poor water quality.

How often do I need to replace the filters in my reverse osmosis system?

In our experience, you should replace the filters or filter cartridges in your reverse osmosis system at least once per year. If a filter gets clogged or damaged, replace it sooner. Some reverse osmosis systems have warning systems that tell you when a filter is failing or nearing the end of its life.

More Tap Water Products

• Best Water Test Kit
• Best Water Softener
• Best Water Filter
• Best Under Sink Water Filter

Our Methodology

This Old House has empowered homeowners and DIY-ers for more than four decades with top-notch home improvement advice in the form of television programs, print media, and digital content. Our team focuses on creating in-depth product and service review content. To date, we’ve published over 1,600 reviews on products in the home space, including power tools, outdoor equipment, major appliances, kitchen gadgets, electronics, and more that focus on product quality and helpfulness to our readers.

To provide our readers with the best recommendations possible, we rely on several key sources of information to help guide our selection process.

Initial Research : Our research process began by generating a list of reverse osmosis systems with a significant number of verified buyer reviews and an average customer review rating of 4–5 stars. We looked at positive and negative reviews alike, focusing on information from both satisfied and critical buyers. 

Expert Insights : To complement our in-house expertise, our team looked at reviews and videos from trusted publications and independent testers, spoke with subject matter experts, and drew insights from reader contributions.

Final Product Selection : We then began fine-tuning our list by replacing older models with the latest versions and eliminating any discontinued models. From there, we compared each model’s feature set to create a final short list, selecting the best-in-class options for various buyers, budgets, and scenarios.

Once we conclude our research, we craft a comprehensive, user-friendly article of recommended products and additional information to help our readers make the right purchase.

Questions or Comments?

To share feedback or ask a question about this article, send a note to our Reviews Team at [email protected] .

Next Up In Plumbing

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9 Best Water Filters, According to Our Testing

Enjoy clean water from the sink and shower with our top-tested picks.

We've been independently researching and testing products for over 120 years. If you buy through our links, we may earn a commission. Learn more about our review process.

Best Under-the-Sink Water Filter

Aquasana 3-stage max flow under sink water filter.

Best Water Filter Pitcher

Brita everyday water filter pitcher with longlast+ filter.

Best Shower Filter

Jolie the filtered showerhead.

If tap water is your go-to for daily hydration, it might be time to integrate a water filter into your kitchen. Water filters are designed to purify your water by eliminating harmful impurities such as chlorine, lead and pesticides, with the level of removal varying by the filter's sophistication. They can also improve the taste — and in some cases, the clarity — of the water.

You can read more about how we evaluate water filters in our Labs — plus everything you need to know to shop for the best water filter — at the end of this guide. Looking to up your water intake on the go? Check out our guide to the best water bottles.

Simply turn on the tap and get filtered water for up to six months . This under-the-sink filter system eliminates chlorine, heavy metals, cysts, herbicides, pesticides, VOCs and more. It's also the one used in the home of former GH Institute Beauty, Health and Sustainability Lab Director Birnur Aral, Ph.D .

“I use filtered water for absolutely everything from cooking to coffee-making, so tabletop water filters can’t keep up with my use,” she says. “With this one, there's no need to refill any carafes or tanks.” It has a high flow rate, however it requires installation.

As one of our top-tested water filters, Brita's Longlast+ filter removed more than 30 contaminants such as chlorine, heavy metals, carcinogens, endocrine disruptors and more. We appreciated its speedy filtering, coming in at 38 seconds per cup. Compared to its predecessor, it lasts six months rather than two, and it doesn’t leave black carbon specks in the water.

Former GH Institute Chief Technologist and Executive Technical Director Rachel Rothman uses this water pitcher in her five-person household. She loves the taste of the water and that she did not have to constantly change the filter. One minor downside is that it needs to be washed by hand.

Unofficially dubbed the "shower head of the Internet," Jolie has certainly become one of the most popular, particularly for its sleek design. Our extensive home testing confirmed that it does live up to the hype. Unlike other shower filters we've tested , the Jolie Filtered Showerhead is an all-in-one design that takes minimal effort to set up. GH Commerce Editor Jacqueline Saguin said it took her about 15 minutes to set up.

We found that it offers excellent chlorine filtration. Its filter contains a proprietary blend of KDF-55 and calcium sulfate, which the brand claimed is better than typical carbon-based filters at capturing contaminants from hot, high-pressure shower water. After nearly a year of use, Saguin noticed "less scale buildup near the drain of the tub," adding that the "water feels softer without any sacrifice in pressure."

Keep in mind that the cost of the shower head itself is steep as is the price of the replacement filters.

LifeStraw Home 7-Cup Glass Water Filter Pitcher

Weighing in at a mere 6 pounds when filled, this small but mighty glass water filter pitcher was lightweight and easy to hold and pour during our tests . Also available in plastic, it improves the taste and clarity of water. Just note that you'll need to refill it more often since it only holds 2.5 cups of tap water and we found that it filtered slowly.

What's more, this water pitcher uses two types of filters: a membrane microfilter and an activated carbon and ion exchange filter. Our review of the brand's third-party lab test data confirmed that it removed more than 30 contaminants , including chlorine, microplastics, sediment, heavy metals, VOCs, endocrine disruptors, pesticides, pharmaceuticals, E.coli bacteria and cysts.

Brita Water Bottle with Filter

Brita is a brand that consistently performed well in our Lab tests. One tester said they loved this bottle for travel because they could fill it up anywhere and know that their water would taste fresh. The bottle is available in stainless steel or plastic — testers found the double-walled stainless steel kept water cool and crisp all day long.

It's also available in a 26-ounce size, which fits most cup holders, or a 36-ounce size, which is handy if you're on a longer trek or can’t refill as often. Its built-in carrying loop makes it easier to tote around too. Some users noted that the design of the straw made it harder to drink through.

Brita Hub Instant Powerful Countertop Water Filter System

Winning a GH Kitchen Gear Award , the Brita Hub impressed our panel with its countertop water machine that can dispense water manually or automatically. The brand stated that you can go six months until replacing the filter. However, GH Institute Kitchen Appliances and Innovation Lab Director Nicole Papantoniou has only had to change the filter once every seven months.

"It has a large capacity, so you don’t need to fill it up as often. [I] love the automatic pours because I can walk away while it fills up, " Papantoniou says. The one negative flagged by our pros? Once the red light turns on to change the filter, it stops working. Just make sure you have extra filters in stock.

Larq PureVis Pitcher with Advanced Water Filter

The Larq PurVis Pitcher filters over 45 contaminants such as microplastics, heavy metals, VOCs, endocrine disruptors, PFOA and PFOS, pharmaceuticals and more. This pick also takes it a step further by using UV light to deactivate E. coli and Salmonella , which can build up in water filter pitchers when chlorine is filtered out.

In testing, we loved that the Larq app was easy to use and that it keeps track of when you need to change the filter, so there’s no guessing. It pours smoothly without splashing, and it’s dishwasher safe, except for the small rechargeable wand, which we found easy to wash by hand. Take note: The filters can be pricier than others.

Soma Glass Carafe

You can proudly display this water filter pitcher on your table when company is over, thanks to its sleek, modern appearance. Not only does it stand out with its unique design, but our pros love that the hourglass shape makes it easy to hold.

It filters out chlorine and four heavy metals including cadmium, copper, mercury and zinc with its cleverly disguised cone filter at the top of the carafe. Our pros found this was easy to set up, fill and pour, however it needs to be washed by hand.

Culligan Faucet-Mount Advanced Water Filter

“It’s easy to install, inexpensive and tested to ANSI standard 42 and 53, so it is built to do a solid job filtering many contaminants,” says GH Home Improvement and Outdoor Lab Director Dan DiClerico . He especially liked the design and the fact that Culligan is a well-established brand.

This filter allows you to switch easily from unfiltered to filtered water with a simple pull of a diverter valve, and no tools are required to install this faucet filter. It filters out chlorine, sediment, lead and more. One drawback is that it makes the faucet bulkier.

How we test water filters

In the Good Housekeeping Institute , our team of engineers, chemists, product analysts and home improvement experts work together to determine the best water filters for home. We've tested more than 30 water filters over the years and continue to scan the market for new options.

To test water filters, we take into account their capacity, how easy they are to set up and, if applicable, how easy they are to pour from. We also read each instruction manual for clarity and look at whether pitcher models are dishwasher safe. We test performance factors like how quickly it filters a cup of water and measure how much water the tap water reservoir can hold.

We also verify contaminant removal claims via third-party data. We review how long each filter lasts as well as the yearly cost to replace filters when changing filters on the manufacturer's recommended schedule.

What to look for when shopping for the best water filter

✔️ Type and capacity: For pitchers, water bottles and other dispensers that hold water after it’s filtered, you’ll want to keep in mind size and weight. Larger containers are ideal for refilling less often, but they will often be heavier and may take up more space in the fridge or your backpack. A countertop model saves space in the refrigerator and often holds more water, but it requires room on the counter and will be room temperature water.

With under-the-sink water filters, faucet filters, shower filters and whole-house filters, there’s no need to worry about size or capacity as these instantaneously filter water as it flows through.

✔️ Filtration method: One thing to note is that many filters incorporate multiple filter types to achieve various contaminant removal. With some, the contaminants they remove can vary widely, so it's best to check what the model actually filters, so it suits your needs. The surest way to determine this is by checking which NSF standard the filters are certified for. For example, some standards cover only lead, like NSF 372 , while others also include agricultural and industrial toxins, like NSF 401 . Otherwise, here are the different water filtering methods:

• A ctivated carbon is the most common water filter. The carbon-based filter acts like a magnet, absorbing contaminants from the water. Multi-stage filters, or 2-stage filters, might also include a pre-filter to remove larger sediment, as well as a second carbon filter to improve odor and taste. If necessary, sometimes there is even a third filter, maybe with an additional carbon block or a UV sterilizer to kill bacteria and viruses.
• Reverse osmosis (RO) is a newer type of filter that captures contaminants by pushing pressurized water through a semi-permeable membrane. While extremely effective, it's more expensive and less efficient — many systems require a tank that won't fit under your sink. Reverse osmosis filters are only seen with water systems because it needs pressure to work. Our experts first recommend testing your water to determine whether a conventional filter can cover your filtering needs. Most water filters use either a carbon filter or a reverse osmosis water filter, which can also include a carbon filter.
• U ltrafiltration (UF) is another technology you might also hear about. Like RO, it forces water through semipermeable membranes. Because the pore size of the UF membranes is bigger, these systems don't capture all contaminants, including total dissolved solids (TDS) like chlorine and fluoride; we did not review any UF systems for this reason.
• Mineral/alkaline filter adds minerals like potassium, magnesium and calcium. According to the Mayo Clinic, alkaline water has a higher pH level than plain tap water. Some studies also suggest that alkaline water might help slow bone loss . However, further studies are needed to determine whether these benefits are long-term.

✔️ Filter replacement frequency: Check how often you have to replace the filter. If you dread changing the filter or simply forget, you may want to look for a long-lasting filter. Also, if you buy filters for the shower, water pitcher and sink, you’ll have to remember to change each of those separately, so it might be smart to consider a whole-house filter that requires only one filter replacement for the entire home.

No matter which water filter you opt for, it’s no good if you don’t change the filter as recommended. “The performance of the water filter depends on the quality of the water source and whether or not the filters are replaced regularly,” Aral says. Some models come with indicators, but if a model doesn’t include one, a slower flow rate or different-colored water are signs that you need to change the filter.

✔️ Price: Consider both the upfront price of the water filter device and the filter refill costs. A water filter could cost more initially, but the price and frequency of the filter refills may save money over the long term. But that’s not always the case, so be sure to calculate the yearly cost of replacements based on the recommended schedule for changing.

Do you really need a water filter?

Access to safe drinking water is an issue across the globe, and it affects communities in the United States. If you’re not sure about your water quality, the Environmental Working Group (EWG) updated its Tap Water Database in 2021. It’s free and easy to search, and it has information for all states.

Enter your zip code or search your state to find details on your drinking water quality based on EWG standards (which are stricter than those of the government). If your tap water does exceed EWG health guidelines, it may be a good idea to consider buying a water filter.

Opting for bottled water is a short-term solution to potentially unsafe drinking water, but it creates a larger problem with serious long-term implications around pollution. Americans throw away a whopping 30 million tons of plastic a year , only 8% of which is recycled. The majority ends up in landfills because there are many different regulations about what can be recycled. Your best bet is to get a water filter and a cute reusable water bottle — some even have filters built-in.

Why trust Good Housekeeping?

This article was written and tested by Jamie (Kim) Ueda , who is an analyst (and consistent user!) of water filtration products. She’s a freelance writer specializing in product testing and reviews. For this list, she tested several water filters and worked with experts across several Good Housekeeping Institute Labs: Kitchen Appliances and Innovation; Beauty, Health, and Sustainability; Home Improvement and Outdoors; and Media and Tech.

Nicole Papantoniou contributed insight on the ease of use of pitchers and bottles. Birnur Aral, Ph.D. helped evaluate the contamination-removal claims behind each of our picks. Dan DiClerico and Rachel Rothman provided expertise on installed filters.

Jamie Ueda is a consumer products expert with over 17 years of experience in areas of product development and manufacturing. She has held leading roles at both mid-size consumer goods companies and one of the most notable and largest apparel brands in the world. Jamie has contributed to several of the GH Institute Labs, including Kitchen Appliances, Media and Tech, Textiles and Home Appliances. In her free time she enjoys cooking, traveling, and working out.

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JSmol Viewer

Comparing conventional and advanced approaches for heavy metal removal in wastewater treatment: an in-depth review emphasizing filter-based strategies.

1. Introduction

2. heavy metals: sources and toxicity.

3. Elimination of Heavy Metals from Wastewater: Conventional Methods

3.1. coagulation and flocculation, 3.2. precipitation, 3.3. ion exchange, 3.4. flotation, 3.5. electrochemical separation, 4. elimination of heavy metals from wastewater: advanced methods, 4.1. membrane filtration, 4.2. adsorption, 4.2.1. filters: classification and applications, synthetic filters, natural filters, hybrid filters, 4.2.2. adsorbents regeneration/reuse, 5. comparison between filters and other methods, 6. conclusions and perspectives, author contributions, institutional review board statement, data availability statement, conflicts of interest.

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Ayach, J.; El Malti, W.; Duma, L.; Lalevée, J.; Al Ajami, M.; Hamad, H.; Hijazi, A. Comparing Conventional and Advanced Approaches for Heavy Metal Removal in Wastewater Treatment: An In-Depth Review Emphasizing Filter-Based Strategies. Polymers 2024 , 16 , 1959. https://doi.org/10.3390/polym16141959

Ayach J, El Malti W, Duma L, Lalevée J, Al Ajami M, Hamad H, Hijazi A. Comparing Conventional and Advanced Approaches for Heavy Metal Removal in Wastewater Treatment: An In-Depth Review Emphasizing Filter-Based Strategies. Polymers . 2024; 16(14):1959. https://doi.org/10.3390/polym16141959

Ayach, Jana, Wassim El Malti, Luminita Duma, Jacques Lalevée, Mohamad Al Ajami, Hussein Hamad, and Akram Hijazi. 2024. "Comparing Conventional and Advanced Approaches for Heavy Metal Removal in Wastewater Treatment: An In-Depth Review Emphasizing Filter-Based Strategies" Polymers 16, no. 14: 1959. https://doi.org/10.3390/polym16141959

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Urban Company Native by UC M1 RO+UV+Copper+Alkaline Water Purifier for Home| Needs No Service For 2 Yrs| 10-Stage Filtration| 4-in-1 Health Booster| 8L Capacity| 2 Year Warranty(Filters Included)

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• Free installation and demo on Televisions. **Installation at the time of delivery available in select pincodes View details .Wall mount brackets are chargeable if not included in the box along with the TV
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RO+UV+Copper+Alkaline 10 Stage Purifier

RO+UV+UF 10 Stage Purifier (Old)

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Material Polypropylene Capacity 8 litres Included Components Water Purifier,Installation Kit,External Sediment Filter,UserManual&WarrantyCard Item Weight 8.6 Kilograms About this item Introducing 2 year filter life: Save up to ₹13,500 on total ownership and service costs over 6 years with smart rinse technology that needs no service for 2 years. (Tested in government-certified labs up to 1500ppm TDS, 100ppm hardness, and 1 NTU turbidity. Actual results may vary based on water input) 10-stage water purification: Aqua purification comprises 10 crucial stages, including UV, copper charged filter and providing water enriched with alkaline, and essential minerals.US FDA certified 99.99% pure water 2 year unconditional warranty: All filters, membranes & electrical parts changes covered at zero service cost. Avail warranty in one-click from the Urban Company app In-tank UV: Enhances water safety with continuous UV light in the tank, eliminating germs, bacteria, and viruses for 24X7 protection against infections providing mineral-enriched, pure, and safe RO water Ideal for all water sources: Tanker, borewell, municipal and tap water - 8 liter storage: 8L food grade tank which keeps the water mineral-enriched and free from harmful chemicals making it fit for consumption. Suitable for home & office Free installation by Urban Company at your preferred date and time. In high rise buildings where input pressure exceeds 30 PSI, a Pressure Reducing Value will be installed at an additional cost of ~₹250. In low rise building and independent houses where input pressure is below 5 PSI, a Pressure Enhancing Kit will be installed at an additional cost up to ~₹500 Box contents: Water Purifier, Pre-filter, installation kit, digital user manual & warranty card Native by UC 89% positive ratings from 1K+ customers 5K+ recent orders from this brand Highly rated by customers for Brand in this category on Amazon Product information Technical details. Brand ‎Native by UC Manufacturer ‎Urbanclap Technologies India Pvt. Ltd. Country of Origin ‎India Model number ‎RO+UV+Copper+Alkaline 10 Stage Purifier Number of Memory Sticks ‎1 Special Feature ‎Needs no service for 2 years Item Weight ‎8 kg 600 g Package Dimensions ‎60.1 x 30.1 x 20.1 cm; 8.6 kg Item model number ‎RO+UV+Copper+Alkaline 10 Stage Purifier Additional Information ASIN B0D79G62J3 Customer Reviews 4.4 out of 5 stars Best Sellers Rank #1,920 in Home & Kitchen ( ) #10 in Date First Available 17 June 2024 Manufacturer Urbanclap Technologies India Pvt. Ltd. Packer Urbanclap Technologies India Pvt. Ltd., 7th & 8th Floor, Plot No. 183, Udhyog Vihar, Sector 20, Rajiv Nagar, Gurugram - 122016 Generic Name Native M1 Water Purifier 10 Stage Fields with an asterisk * are required : : : : : Please select province : : to provide feedback. \n' + ' ' ); } function getThankYouDiv(thankMsg) { return ( ' \n' + ' ' ); } function getLoadingGifDiv() { return ' What is in the box? Water Purifier,Installation Kit,External Sediment Filter,UserManual&WarrantyCard Product description Introducing a revolutionary product in India – the Urban Company Native M1 Water Purifier. Unlike others, it only needs servicing once every two years! Thanks to our smart rinse technology with multi-micron filtration, the filters can last up to 2 years, delivering a whopping 12,000 litres of pure water in each service cyle. Rest assured, it’s US FDA-certified, ensuring 99.99% pure water through a 10-stage filtration process: RO, UV, Copper, Alkaline and essential minerals. Inside the 8L food-grade water tank, integrated UV light eliminates harmful bacteria and viruses, keeping you and your family safe from waterborne diseases. It works seamlessly with all water sources – tankers, borewells, and municipal water, even handling TDS levels up to 2000 PPM. Enjoy a user-friendly experience with a retractable tray. And that’s not all – we offer installation, a pre-filter, and an unconditional 2-year warranty for free. Brands in this category on Amazon Looking for specific info? Customer reviews. Customers say Customers like the value, quality and performance of the water purification unit. For example, they mention it's worth every penny, the taste of thewater is good and the performance is good. They're also happy with ease of installation, water quality, and appearance. That said, opinions are mixed on service. AI-generated from the text of customer reviews Customers like the quality of the water purification unit. They say it's excellent, works well, and has a nice design. Some say that the water taste is good. "...has several stages and the looks of the purifier is classic and awesome . The water has 7 litre storage and it can fill in under 30 minutes...." Read more " Amazing product . Fits in ur pocket and with all features of other stablised brands. Service is super lightning...." Read more "M1 water purifier is working very well . Urban company's service and installation time is excellent. The company did the installation the next day...." Read more "Plus- Nice design, good functioning and operator support, 2 years complete free services...." Read more Customers find the installation of the water purification unit to be easy. They mention that the installation is quick, the staff is supportive, and the installation was completely free. Customers also say that the water is tasty and that the men who did the installation were patient and professional. "...The installation is completely free . Water tasted a bit different initially, but later it tasted exactly like mineral water bottle...." Read more "...The installation was smooth and efficient , with careful attention to detail...." Read more "The overall experience was really good. Installation happened seamlessly . Service provider was experienced and he explained all the things...." Read more "It's very easy to use . Water is very tasty. One thing to think about something outlet water speed is very fast otherwise all over ok" Read more Customers are satisfied with the appearance of the water purification unit. They mention that it has an elegant, classic black and glass look. Some appreciate the modern and suiting kitchen well appearance. They also appreciate the UV light placed on top of the tank. Overall, most are happy with the product's appearance and functionality. "...This water purification has several stages and the looks of the purifier is classic and awesome...." Read more "...The service person did an excellent job fitting the filter . They were professional, punctual, and highly knowledgeable about the product...." Read more "...Good taste of water- low maintenance- Sleek design ..." Read more "...Value for money water purifier. Size of the purifier is adequate ." Read more Customers are satisfied with the taste of the water purification unit. They mention that the finishing is eligenent and the taste is good. "- Good purification- Good taste of water- low maintenance- Sleek design..." Read more "It's very easy to use. Water is very tasty . One thing to think about something outlet water speed is very fast otherwise all over ok" Read more "No more wastage of water, taste also good " Read more "...Water TDS reduced from 370 to 85. Taste also good with copper " Read more Customers appreciate the value of the water purification unit. They mention that it works excellent, the AMC cost is covered very well, and the warranty for 2 years is the best. They also say that it has many features at this small price and is worth buying. "...Extremely satisfied and the price is also very reasonable . Thanks UC" Read more "... Value for money water purifier .Size of the purifier is adequate." Read more " Money saver , i suggest M1 over M2Next day installment. Good support from the company on usage...." Read more " Value for money Ease of use." Read more Customers like the water quality of the water purification unit. They mention that the sound it makes less and the water purity is also quite good. They appreciate the water performance, saying that it works really well and provides filtered and safe water. Customers also say that it reduces the TDS of the Water and gives the better taste. "...Checked TDS before and after installation Water quality is good Storage capacity" Read more "...Installation done on same day of delivery. Water quality is good ." Read more " No more wastage of water , taste also good" Read more "Excellent purifier works really well ...... water purification is very good ." Read more Customers like the performance of the water purification unit. They mention that it's efficient, fast, and does the job well. Some appreciate the fast water speed, filtration, and filling. "...Water is very tasty. One thing to think about something outlet water speed is very fast otherwise all over ok" Read more "good test and very fast filling " Read more "...8l of tank capacity is very good. The filtration is reasonably fast and taste is good." Read more "...Dropping 2 stars for extremely poor after sales service and low quality parts...." Read more Customers are mixed about the service. Some mention that the water quality is good, the installation was quick, and the service professional was very good. However, others say that the service is poor, third-party service is poorly provided, and there is a lack of proper training. The delivery time is long and there was no response to installation thereafter. "...They were professional, punctual , and highly knowledgeable about the product...." Read more "... Service is super lightning . Installation done on same day of delivery. Water quality is good." Read more "It's a nice product but only con is slow water dispenser . I would expect in next version it should improve...." Read more " Good service quality , and as lots of people getting this installed, the service was delayed that is why I have given 4 rating, else I would have..." Read more Reviews with images Sort reviews by Top reviews Most recent Top reviews Top reviews from India There was a problem filtering reviews right now. please try again later.. Press Releases Amazon Science Sell on Amazon Sell under Amazon Accelerator Protect and Build Your Brand Amazon Global Selling Become an Affiliate Fulfilment by Amazon Advertise Your Products Amazon Pay on Merchants COVID-19 and Amazon Your Account Returns Centre Recalls and Product Safety Alerts 100% Purchase Protection Amazon App Download Conditions of Use & Sale Privacy Notice Interest-Based Ads 143 IMAGES Installing RO Water Purifier Reduces Your Risk to Exposure of Deadly What is RO water Purifier? (Working, Advantages and Disadvantages) RO Water Purifier For Healthy And Balanced Water In What Ways Does RO Water Purifier Work ? Basic features of commercial ro water purifier by Soumya Singh Pureit Vital Max RO Water Purifier Review VIDEO Presenting world's first RO that saves 20,000 litres of water. Join the movement now RO WATER ஏன் சுவையா இருக்கு Best RO Water Purifier in India RO water purifier 💦🌊🌊 moter rotation ro water purifier starting just RS 4999 contact 8087966476 🧑‍🔧 Ro Water purifier service 🧑‍🔧#rowaterpurifier #ropurifications #roservice #bmsaqualife #kolkata COMMENTS (PDF) Reverse Osmosis Technology, its Applications and ... Osmosis membrane technology. Reverse Osmo sis (RO) i s a method of obtaining pure water from water co ntaining a salt, as in. desalination [1]. It is a water purification technology that uses a ... A Short Review on Process and Applications of Reverse Osmosis Reverse Osmosis (RO) is a membrane based process technology to purify water by separating the d issolved. solids from feed stream resulting in per meate and reject stream fo r a wide range of ... A Review on Reverse Osmosis and Nanofiltration Membranes for Water Sustainable and affordable supply of clean, safe, and adequate water is one of the most challenging issues facing the world. Membrane separation technology is one of the most cost-effective and widely applied technologies for water purification. Polymeric membranes such as cellulose-based (CA) membranes and thin-film composite (TFC) membranes have dominated the industry since 1980. Although ... A Review on Reverse Osmosis and Nanofiltration Membranes for Water This paper critically reviews the growth and achievement in organic and inorganic membrane studies for RO and NF procedures. The review will start by introducing the synthesis method and structural properties of recent RO and NF membranes, followed by discussing and comparing water purification performance of representative RO and NF membranes made from organic and inorganic materials. Reverse osmosis desalination: A state-of-the-art review Abstract. Water scarcity is a grand challenge that has always stimulated research interests in finding effective means for pure water production. In this context, reverse osmosis (RO) is considered the leading and the most optimized membrane-based desalination process that is currently dominating the desalination market. A Review on Reverse Osmosis and Nanofiltration Membranes for Water This review provides insight into. synthesis approaches and structural properties of recent reverse os mosis (RO) and nanofiltration. (NF) membranes which are used to retain dissolved species such ... PDF Reverse Osmosis (Ro) Filtered Water: Random Sampling, Analysis and It is seen from literature review that RO technology is used to remove dissolved solids, colour, organic contaminants, and nitrate from feed stream. RO-filtered water, samples were collected ... While water purifiers ensure that we drink only pure water, most RO water purifiers also remove the essential minerals from the water. WHO has been ... A comprehensive review of membrane-based water filtration ... The purification of water is not only essential for human consumption but is becoming a necessity considering the limited freshwater reserves of the planet. Over the last few decades advancements in material sciences and technology have paved the way for the development of novel purification techniques. Amongst these techniques membrane-based filtration is considered as the least expensive and ... Appropriate household point-of-use water purifier selection template Description of purifier alternatives Thermal or light based treatment techniques Boiling. Boiling is perhaps the oldest method of water purification (Sobsey 2002) but is a highly energy intensive one.One minute of boiling at a temperature 100 °C (at mean sea level) ensures neutralisation of faecal and thermo-tolerant coliforms, protozoan cysts and viruses (Sobsey 2002; Loo et al. 2012). PDF A Short Review on Process and Applications of Reverse Osmosis 1.0 Introduction: Reverse Osmosis (RO) is a process that uses semi-permeable spiral wound membranes to separate and remove dissolved solids, organic, pyrogens, submicron colloidal matter, color, nitrate and bacteria from water. Feed water is delivered under pressure through the semi permeable membrane, where water permeates the minute pores of ... PDF Solar Based Reverse osmosis water purification system Reverse osmosis water purification stages : A solar-based RO (Reverse Osmosis) water purification system uses solar energy to power the water purification process. The process involves several stages, including: 1. Water Intake: The water to be purified is drawn from a source, such as a well or a lake, and fed into the system. 2. PDF Solar Powered Reverse Osmosis Water Purifier To design and construct a reverse osmosis unit, powered by solar energy, capable of producing drinkable water from brackish borehole feed for rural households or small communities. Flood affected area. Military applications in remote places. To motivate peoples about renewable energy resources by using solar RO system. Reverse Osmosis Literature Review 1 Search Terms. 1.1 Google Scholar; 2 Reverse Osmosis; 3 Importance of Reverse Osmosis; 4 Literature. 4.1 A Review on Reverse Osmosis and Nanofiltration Membranes for Water Purification; 4.2 Nanoparticles in reverse osmosis membranes for desalination: A state of the art review; 4.3 Desalination Technologies for Developing Countries: A Review; 4.4 Sustainable seawater reverse osmosis (SWRO ... PDF Water Purification System Powered By Solar Energy From literature review, it is found that numerous methods are developed for treatment of water for domestic use. Conventional, Reverse Osmosis systems are used domestically, but at the cost of waste water. Non-conventional water cleansers like a solar still have unlimited potential, but output is limited. Application of reverse osmosis in purifying drinking water Reverse osmosis (RO) uses a mechanical pump to utilize pressure on drinking water. It offers many benefits, including the ability to function at ambient temperature, it does not require any ... PDF Consumer'S Attitudes Towards Kent Water Purifier REVIEW OF LITERATURE 1. Dr.V.Maheswari (2019), The study examined purified drinking water is essential to every citizen. To know the level of satisfaction on water purifier and problem faced by the respondents in using the water purifier. She found that majority 69% of the respondent were satisfied overall performance of the brand. "Review of Solar Powered Reverse Osmosis Water Purifier" This paper is intended true make use of solar energy by using solar PV cells for residential application. Also if modified the proposed model of solar RO water purifier can be made portable and extend its application area. The use of solar PV cell along with suitable controller circuits for RO water purification (small capacity). Controller circuit consisting charge controller which increase ... Our 7 Best Reverse Osmosis System Picks (2024) Investing in and installing a reverse osmosis water filter gives you cleaner, more pure water by removing dirt, chemicals, microorganisms, heavy metals, and other contaminants and impurities. These systems can vary greatly in price, with budget-friendly models starting around $150-$300 and higher-end systems running anywhere from $500-$1,000.. Our team has reviewed some of the best reverse ... Cloud RO Water Filtration System Review & Comparison Cloud RO retails for $750 but is often on sale for a much lower price. In other words, Cloud RO isn't the cheapest under-the-sink RO system on the market, but it's not the most expensive one either. For example, our Radiant Life 14-In-1 system retails for around $1,700. Technical Report On RO Water Purification Plant This document provides information on a reverse osmosis (RO) water purification plant. It discusses that RO plants use semi-permeable membranes to remove ions, molecules, and particles from water to make it safe for consumption. The main components of an RO system are described, including filters, membranes, tanks, and a pump. The process of RO works by applying pressure to push water through ... PDF A Review on Solar Powered Water Purification Nayara K. G, et al. (2017): They proposed electro dialysis (ED) over reverse osmosis (RO) for water purification in the urban area of India which outperforms RO and can achieve a recovery of 80%, producing 12 L/h of water at the desired salinity of 350 ppm from a feed salinity of 3000 ppm. The cost and size of the proposed system are also 9 Best Water Filters of 2024, Tested & Reviewed by Experts Reverse osmosis (RO) is a newer type of filter that captures contaminants by pushing pressurized water through a semi-permeable membrane. While extremely effective, it's more expensive and less ... (PDF) PORTABLE WATER PURIFICATION SYSTEM Reverse Osmosis (RO) system as a main membrane is the suitable filter to use for this project because it capability to separate the particle in the contam inated water with fast and low pressure ... KENT Prime Plus RO Water Purifier Find helpful customer reviews and review ratings for KENT Prime Plus RO Water Purifier | 4 Years Free Service | Multiple Purification Process | RO + UV + UF + TDS Control + UV LED Tank | 9L Tank | 20 LPH Flow | Zero Water Wastage | Digital Display at Amazon.com. Read honest and unbiased product reviews from our users. Polymers Various industrial activities release heavy metal ions into the environment, which represent one of the major toxic pollutants owing to their severe effects on the environment, humans, and all living species. Despite several technological advances and breakthroughs, wastewater treatment remains a critical global issue. Traditional techniques are dedicated to extracting heavy metal ions from ... Development of solar-powered water purification systems The design of a solar-powered water purification system is based totally on the thermal. method by using the thermal heating system principle which converts sunlight rays into heat. The most vital ... Urban Company Native by UC M1 RO+UV+Copper+Alkaline Water Purifier for Aquaguard Sure Delight NXT RO+UV Water Purifier | Free Service Plan worth ₹2000 | India's #1 Water Purifier | Suitable for Borewell, Tanker & Municipal Water | 30x Impurity Removal vs Local Purifiers ... Top review from India There was a problem filtering reviews right now. Please try again later. Gabagandu. 5.0 out of 5 stars Good product. assignment essay homework paper phd report resume review thesis