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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 ].

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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.

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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.

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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.

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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.

Nanofiltration for drinking water treatment: a review

  • Review Article
  • Published: 26 November 2021
  • Volume 16 , pages 681–698, ( 2022 )

Cite this article

literature review on ro water purifier

  • Hao Guo 1   na1 ,
  • Xianhui Li 2   na1 ,
  • Wulin Yang 3 ,
  • Zhikan Yao 4 ,
  • Ying Mei 5 ,
  • Lu Elfa Peng 1 ,
  • Zhe Yang 1 ,
  • Senlin Shao 6 &
  • Chuyang Y. Tang 1  

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In recent decades, nanofiltration (NF) is considered as a promising separation technique to produce drinking water from different types of water source. In this paper, we comprehensively reviewed the progress of NF-based drinking water treatment, through summarizing the development of materials/fabrication and applications of NF membranes in various scenarios including surface water treatment, groundwater treatment, water reuse, brackish water treatment, and point of use applications. We not only summarized the removal of target major pollutants (e.g., hardness, pathogen, and natural organic matter), but also paid attention to the removal of micropollutants of major concern (e.g., disinfection byproducts, per- and polyfluoroalkyl substances, and arsenic). We highlighted that, for different applications, fit-for-purpose design is needed to improve the separation capability for target compounds of NF membranes in addition to their removal of salts. Outlook and perspectives on membrane fouling control, chlorine resistance, integrity, and selectivity are also discussed to provide potential insights for future development of high-efficiency NF membranes for stable and reliable drinking water treatment.

literature review on ro water purifier

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Acknowledgements

This work is supported by Senior Research Fellow Scheme of Research Grant Council (Grant No. SRFS2021-7S04) in Hong Kong and Seed Fund for Translational and Applied Research at The University of Hong Kong, China (Grant No. 104006007).

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These authors contributed equally to this work.

Authors and Affiliations

Membrane-based Environmental & Sustainable Technology (MembEST) Group, Department of Civil Engineering, The University of Hong Kong, Hong Kong, China

Hao Guo, Lu Elfa Peng, Zhe Yang & Chuyang Y. Tang

Key Laboratory for City Cluster Environmental Safety and Green Development of the Ministry of Education, Institute of Environmental and Ecological Engineering, Guangdong University of Technology, Guangzhou, 510006, China

College of Environmental Science and Engineering, Peking University, Beijing, 100871, China

College of Chemical and Biological Engineering, Zhejiang University, Hangzhou, 310027, China

Research and Development Center for Watershed Environmental Eco-Engineering, Advanced Institute of Natural Sciences, Beijing Normal University, Zhuhai, 519087, China

School of Civil Engineering, Wuhan University, Wuhan, 430072, China

Senlin Shao

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Correspondence to Senlin Shao or Chuyang Y. Tang .

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Guo, H., Li, X., Yang, W. et al. Nanofiltration for drinking water treatment: a review. Front. Chem. Sci. Eng. 16 , 681–698 (2022). https://doi.org/10.1007/s11705-021-2103-5

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Received : 13 May 2021

Accepted : 28 July 2021

Published : 26 November 2021

Issue Date : May 2022

DOI : https://doi.org/10.1007/s11705-021-2103-5

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Reverse Osmosis Literature Review

literature review on ro water purifier

  • 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
  • Literature reviews
  • FAST literature reviews
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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.

Waterdrop G3P800 8-Stage Tankless RO System Logo

Reverse Osmosis System Overall

Waterdrop G3P800 8-Stage Tankless RO System

AquaTru 4-Stage Countertop RO System Logo

Best Countertop Reverse Osmosis System

Aquatru 4-stage countertop ro system.

APEC Water Systems ROES-50 5-Stage RO System Logo

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.

Product Card Image

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

Product Card Image

  • $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

Product Card Image

  • $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

Product Card Image

iSpring 6-Stage Reverse Osmosis System

  • $197.09 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

Product Card Image

Express Water RO5DX 5-Stage Under Sink RO System

  • $169.99 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

Product Card Image

Whirlpool WHAROS5 RO Water Filtration System

  • $173.35 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

Product Card Image

Ecoviva Countertop Reverse Osmosis System

  • $201.37 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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Best water purifier (April 2024): Trust these top 10 picks for clean, safe, & healthy drinking water

Best water purifiers: give your home safe and cleaner drinking water to assure your family's good health. here are our top 10 picks..

The importance of a water purifier cannot be ignored for the fact that your health primarily relies upon safe and clean drinking water. And that can only be attained if we install a water purifier at our place. A great water purifier gives the assuring that you get clean and safe drinking water, thereby also assuring your health. 

Best water purifier: Premium water purifiers not only filter and clean water but also retain its essential minerals.

By employing a variety of filtration and purification methods, water purifiers effectively remove impurities, contaminants, and harmful microorganisms from water sources.

While there are numerous brands, each encouraging the best outcomes in regard to immaculateness of water, picking the best for your family can be an overwhelming undertaking. Nonetheless, on the off chance that you want to purchase another water purifier for yourself, we can help you in tracking down the right one for you.

We have created this rundown of top 10 water purifiers that will not only help you get safe and clean water to drink, but will also ensure that your family and loved ones stay in the pink of their health.

Let's dive into the details and help you pick the best water filter for your family's daily needs.

Livpure GLO PRO++ RO+UV+UF, Water Purifier for Home - 7 L Storage, Suitable for Borewell, Tanker, Municipal Water (Black)

The Livpure GLO PRO++ RO+UV+UF Water Purifier is a reliable solution for clean and healthy drinking water. This advanced purifier combines multiple purification technologies – Reverse Osmosis (RO), Ultraviolet (UV), and Ultrafiltration (UF) – to ensure that your water is free from impurities, bacteria, viruses and harmful contaminants. The RO membrane effectively removes dissolved solids, heavy metals, and chemicals, while the UV chamber sterilizes water by deactivating microorganisms. Additionally, the UF filter provides a final layer of filtration to ensure crystal-clear water.

Specifications of the Livpure GLO PRO++ RO+UV+UF Water Purifier

Purification Technology: RO, UV, UF

Storage Capacity: 7 Litres

Purification Capacity: Up to 15 litres per hour

Input Water Temperature: 10 Degree Celsius to 40 Degree Celsius

Operating Voltage: 140-300 V AC/50 Hz

Installation: Wall-Mounted

Dimensions (WxDxH): 290 mm x 251 mm x 485 mm

AQUA D PURE 4 in 1 Copper RO Water Purifier with UV, UF and TDS Controller | 12Liter | Fully Automatic Function and Best For Home and Office

AQUA D PURE copper RO water purifier combines elegance with advanced technology. With 8 purification stages, including RO+UV+UF+TDS+Copper, it ensures clean water for homes and offices. The 12 litre storage capacity, purified water level indicator, and automatic shut-off add convenience. The copper filter enhances water quality, and the fully automatic function prevents overflow. This water purifier is perfect for efficient purification with adding elegant design, and the goodness of copper.

Specifications of AQUA D PURE Copper RO Water Purifier

Brand : Aqua

Capacity : 12 L

Special feature : Automatic shut-off

Installation type : Wall mount or table top

Aquaguard Sure Delight NXT RO+UV Water Purifier | 4 Stage Purification | 6L Storage | Suitable for Borewell, Tanker & Municipal Water | From Eureka Forbes

Aquaguard Sure Delight water purifier ensures purity with 4-stage filtration, removing contaminants like lead, mercury, and bacteria. Suitable for various water sources, it features a taste adjuster for personalized water flavour. With a 6L capacity, LED indicators, and flexible installation options, it's a convenient and efficient choice. Save up to 60% water with its superior technology. Enjoy 7 stages of purification in a compact design. Warranty includes 1 year on all parts.

Specifications of Aquaguard Sure Delight NXT RO+UV Water Purifier

Brand : Aquaguard

Capacity : 6 L

Special feature : Energy saving

Installation type : Wall mount or countertop

Native by UC M1 Copper RO+UV+UF+MTDS Water Purifier for Home | Needs No Service For 2 Yrs | 10-Stage Filtration | With Copper & Alkaline | 8L Capacity | 2 Year Warranty (Filters Included)

Experience pure water like never before with the Urban Company Native M1 water purifier. Boasting a remarkable 10-stage filtration system, including, it delivers 99.99% pure water enriched with essential minerals and the goodness of copper. With a generous 8L capacity and smart rinse technology ensuring no service for 2 years, it's a cost-effective choice. The 2-year on-site warranty, covering filters and membranes, along with free installation by Urban Company, guarantees peace of mind for your family's hydration needs.

Specifications of Urban Company Native M1 Copper Water Purifier

Brand: Urban Company

Capacity : 8 L

Special feature : Integrated UV light

Also read: Best water purifiers: Top 10 options to consider for pure and clean water

Havells AQUAS Water Purifier (White and Blue), RO+UF, Copper+Zinc+Minerals, 5 stage Purification, 7L Tank, Suitable for Borwell, Tanker & Municipal Water

The Havells AQUAS water purifier in white and blue ensures pristine drinking water through 100% RO and UF purification. With a 5-stage purification process and a 7L tank, it's suitable for various water sources. The convenient removable transparent tank allows for easy cleaning, and the hygiene zero splash water flow controller faucet adds an extra layer of cleanliness. Its compact design with 3-way mounting provides flexibility in installation. Enjoy the benefits of copper, zinc, and minerals, contributing to a refreshing taste.

Specifications of Havells AQUAS Water Purifier

Brand : Havells

Capacity : 7 L

Special feature : 5 stage purification

HUL Pureit Advanced RO + MF 6 Stage 7Litre wall mounted/counter top water Purifier, Black

This black wall-mounted/counter-top water purifier from HUL boasts a 7-liter capacity and a 6-stage purification system, including reverse osmosis and micro filtration. Engineered with food-grade plastic, it handles TDS up to 2000 ppm. The smart auto-shut off feature, power saving mode, and advanced voltage fluctuation guard ensure optimal performance. Compact dimensions of 30L x 22.2W x 36H centimetres make it versatile for any space, delivering 100% pure RO water.

Specifications of HUL Pureit Advanced RO + MF 6 Stage 7Litre wall mounted

Brand : HUL

Special feature : 6 stage purification

Also read: Best water dispenser with refrigerator: Top 6 options to invest in

AQUA D PURE Copper + Alkaline RO Water Purifier 12L RO+UV+UF Copper+Bio-Alkaline +TDS Control+UV Purified Water with Goodness of Copper and Alkaline RO Water Purifier, Black

Aqua RO water purifier is the perfect solution for pure and alkaline drinking water. This 12L purifier employs an advanced 8-stage purification process ensuring every drop is safe and sweet. The triple-layered RO+UV+UF protection removes impurities, microorganisms, and heavy metals, offering comprehensive water safety. Its versatility extends to purifying various water sources, including borewell, tanker, and tap water, with a TDS control system for mineral retention. With a daily capacity of 285 liters, flexible installation options, and additional features like membrane protection, this is one of the best water purifier for large households.

Specifications of AQUA D PURE Copper + Alkaline RO Water Purifier

Special feature : 8 stage purification

Faber CUV 8000 (UV + UF + Copper)| 7L Storage|7 Stage Filtration Pre & Post Carbon|Upto 500 PPM TDS|Tank Full, Power, Purification Indicator|Suitable for Municipal Water

Faber CUV 8000 water purifier offers safe drinking water through advanced UV and UF purification in its unique 7-stage filtration system. This 7-litre capacity purifier includes features like UV and UF filters, copper guard technology, and activated carbon for healthier, tastier water. Its convenient indicators for tank full, ongoing purification, and low pressure make it user-friendly. However, note that it does not include an RO filter. The absence of RO makes it water-efficient, and the copper component promotes a healthy metabolism.

Specifications of Faber CUV 8000 Water Purifier

Brand : Faber

Special feature : 7 stage purification

Royal Aquafresh Copper Audy Sedimentation 12 Ltr RO+UV+UF+TDS 14 Layer Waterpurification Advance Technology Electric Water Purifier (1 Year Warranty On Pump & SMPS)

Experience advanced water purification with the Royal Aquafresh copper audy sedimentation water purifier. With a 12-liter capacity and 14-layer filtration including RO, UV, UF, and TDS technologies, it ensures clean and healthy hydration. The off-white, wall-mount design with a compact 20x40x50 cm dimension adds convenience to your space.

Specifications of Royal Aquafresh Copper Audy Sedimentation 12 Ltr RO+UV+UF+TDS 14 Layer Water Purifier

Brand : Royal Aquafresh

Capacity: 12 L

Special feature: 14 stage purification

Installation type: Wall mount or countertop

AO Smith Z9 Hot+ normal RO |Baby-Safe Water |Hot Water |10 L Storage|8-Stage Purification |100%RO+SCMT (Silver Charged Membrane Tech.)|Wall mount Water Purifier

This wall-mountable water purifier from the premium brand AO Smith offers 8-stage purification, including 100% RO+SCMT for baby-safe water. Its patented side stream RO Membrane ensures impurity-free water, and one-touch dispensing adds convenience. Enjoy hot water at the touch of a button with three temperature modes. The 10-liter storage capacity, MIN-TECH for natural taste, and high recovery rate make it a versatile choice. Benefit from a 1-year comprehensive warranty and flexible installation options.

Specifications of AO Smith Z9 Hot+ normal RO Baby-Safe Water Purifier

Brand: AO Smith

Capacity: 10 L

Special feature: 8 stage purification

Also Read: Top 10 best water purifiers for clean and safe drinking water

Best 3 features for the best water purifier

Best value for money water purifier in india.

The Urban Company Native M1 Copper Water Purifier stands out as the best value for money with its innovative features and cost-saving benefits. Crafted with precision and designed with elegance, this purifier stands as a testament to Urban Company's commitment to delivering excellence. The 8-litre food-grade tank, integrated UV light, and 2-year zero-cost on-site warranty further enhance its value. With free installation by Urban Company, this water purifier delivers advanced purification.

Also Read: Best water purifiers: Top 10 options to consider for pure and clean water

Best overall water purifier in India

The Livpure GLO PRO++ RO+UV+UF water purifier is the best overall product. This advanced system combines multiple purification techniques – Reverse Osmosis (RO), Ultraviolet (UV), and Ultrafiltration (UF) – to ensure the delivery of pristine drinking water. The RO filtration process effectively eliminates dissolved impurities like heavy metals and salts, while UV sterilization destroys harmful bacteria, viruses, and other pathogens present in the water.

How to find the best water purifier

To find the best water purifier, assess your water quality, considering sources like tap, borewell, or tanker. Identify contaminants and choose a purifier with relevant filtration technology. Evaluate features like purification stages, capacity, and maintenance. Read user reviews, check certifications, and compare prices for a well-informed decision on the ideal water purifier.

Disclaimer: At Hindustan Times, we help you stay up-to-date with the latest trends and products. Hindustan Times has an affiliate partnership, so we may get a part of the revenue when you make a purchase. We shall not be liable for any claim under applicable laws, including but not limited to the Consumer Protection Act, 2019, with respect to the products. The products listed in this article are in no particular order of priority.

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Best RO Water Purifiers To Increase Quality And Infusing Essential Minerals

Best RO Water Purifiers To Increase Quality And Infusing Essential Minerals

  • Take into account the water purifier's storage volume and space requirements. It should meet the existing space in your house for the installation of the product.
  • Find the energy efficiency and operational costs of the filter to be able to deal with long-term expenses appropriately.
  • Prepare a budget in a way that matches your home’s drinking water requirements, storage capacity, space requirements, and operating costs.
  • Include additional features such as UV purification, TDS controller and certification of the product from NSF or WQA if required to satisfy the specific needs and the quality standards. Selection of a purifier that addresses these characteristics guarantees effective performance and you will be happy with your purchase.

HUL Pureit Copper+ Mineral RO + UV + MF 7-stage Tabletop 8 litres Water Purifier

  • Precise copper dosing for health benefits
  • Dual dispensing for choosing between copper-infused water or regular RO water
  • Patented Copper charge technology
  • Intelligent auto-cleaning for maintaining freshness
  • Smartsense indicators notify filter expiry for continuous safe water
  • 1-year warranty

AO Smith Z8 Hot+ normal RO

  • 8-stage purification with RO+SCMT for baby-safe water
  • Patented Side Stream RO Membrane for thorough purification
  • Hot water is available in three temperature modes
  • 10-liter capacity for a steady supply of purified water
  • Hot water with essential minerals stored in a stainless-steel tank that can be accessed at three temperature modes

Aquaguard Aura 7L RO+UV+Taste Adjuster water purifier

  • 8-stage purification system for removal of contaminants for safe drinking water
  • Certified RO+UV technology: Effectively eliminates viruses, bacteria, lead, mercury, and arsenic
  • Active Copper+Zinc Booster Technology enhances the taste and boosts immunity with essential minerals
  • Suitable for all water sources, from borewells to municipal
  • High storage capacity and flexible installation options

Havells Gracia Alkaline Water Purifier

  • 8 stages of 100% RO & UV purification deliver alkaline water with pH 8 to pH 10
  • i-Protect purification monitoring that cuts off the water if it is no longer safe to drink
  • Include maintenance and error alerts, process indicator, digital clock, and zero splash hygienic water dispensing
  • Stainless steel tank enhances the oxygen level in purified water
  • Three temperature modes of water, Child lock protection from hot water
  • LED colour temperature guide

V-Guard RequPro RO Water Purifier

  • 9-stage purification system for removal of contaminants
  • Can save 3X more water than conventional RO systems
  • Water stays fresh, pure, and odourless in the stainless-steel tank
  • Mineral Enhancer and Copper Release Technology for providing essential minerals
  • Made for Indian water source conditions, can treat water with up to 2000 TDS levels
  • Long-Lasting Filters

KENT Supreme Alkaline RO Water Purifier

  • Zero Water Wastage Technology
  • Retains Essential Minerals
  • Makes Water Alkaline
  • UV LED light in its storage tank to keep purified water free of bacteria
  • 1 Year Warranty + 3 Years Extended Service Free
  • Regular Maintenance: Follow the manufacturer's directions for changing your filters and check out using system sanitation. Filters and membranes should be replaced once the designated time frames have elapsed in order to maintain efficiency and quality.
  • Try to sanitize components from time to time to prevent bacterial growth. Clean the purifier regularly to prevent the purifier from jamming and harming its components.
  • Check for leaks or breakdowns and make the repairs in the shortest time possible to prevent damage or contamination.
  • Guard Against Hard Water: Set a water softener in place to lessen the scale formation on membranes and thus make their functioning last for longer periods.
  • Professional Servicing: Periodically arrange for expert technicians or engineers who are qualified and then get them to troubleshoot problems and keep the system operating at high capacity. Installation of these devices guarantees the extended life of your RO purifier by providing it with a clean working environment for the years to come.

author

KENT Prime Plus RO Water Purifier | 4 Years Free Service | Multiple... › Customer reviews

Customer reviews.

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

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

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  1. (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 ...

  2. 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 ...

  3. 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.

  4. 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 ...

  5. 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 ...

  6. 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).

  7. 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.

  8. 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 ...

  9. A review on RO membrane technology: Developments and challenges

    Highlights. •. RO based desalination is one of the most important technologies for the production of fresh water. •. This review highlights about important milestones in RO technology. •. The material property, mainly dominates the RO process. •. Few of the problems associated with RO technology is also discussed.

  10. PDF Membrane fouling in reverse-osmosis filters during real drinking water

    logical fouling. The permeate flux of the purifier recovered to the initial level with new pretreatment filters after 85 d and thus stresses the importance of in-time replacement of pretreatment filters in commercial drinking water purifiers. Keywords: Reverse osmosis; Fouling; Drinking water purification; Surface-enhanced Raman

  11. Nanofiltration for drinking water treatment: a review

    Pype M L, Lawrence M G, Keller J, Gernjak W. Reverse osmosis integrity monitoring in water reuse: the challenge to verify virus removal—a review. Water Research, 2016, 98: 384-395. Article CAS PubMed Google Scholar Mi B, Eaton C L, Kim J H, Colvin C K, Lozier J C, Mariñas B J. Removal of biological and non-biological viral surrogates by ...

  12. 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.

  13. 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 ...

  14. A Study on Consumer Perception and Satisfaction of Water Purifier in

    So it is deeply disturbing to learn that drinking is the main health hazard in India. In India nearly 80% people die due to water related diseases. Both urban and rural areas in India are suffering from scaring of clean water for domestic use. Water purifier is necessary now a day especially if underground water is used for drinking.

  15. 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.

  16. (PDF) RO purifier Working and health implications ...

    of water by RO purifiers. Figure 4: Scale on which people ... The objective of this literature review is to bring . ... seawater reverse osmosis and brackish water reverse osmosis. Differences ...

  17. 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.

  18. 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 ...

  19. 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

  20. Best water purifier (April 2024): Trust these top 10 picks for clean

    Aqua RO water purifier is the perfect solution for pure and alkaline drinking water. This 12L purifier employs an advanced 8-stage purification process ensuring every drop is safe and sweet.

  21. Ro Water Purifier: Best RO Water Purifiers To Increase Quality And

    This RO purification system can also save up to 60% more water than ordinary water purifiers that end up wasting 50-75% water. Key Features 8-stage purification system for removal of contaminants ...

  22. 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.

  23. 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 ...

  24. Brew Better (Not Bitter) with RO Filtration

    EZ-RO enhances coffee, espresso, and tea extraction for an elevated cup, every time. The Remineralization adds a small amount of magnesium and calcium back into your water to neutralize pH levels, while the integrated Water Blending Processor and TDS Monitor allow you to customize your water profile further. 3. That Magic Aroma.

  25. Literature Review On Ro Water Purifier

    341. Customer Reviews. Literature Review On Ro Water Purifier, Thesis Statement On Too Much Homework, Embracing Individuality Essay, Userra Research Papers, Usa Staffing Cover Letter, Cheap Thesis Proposal Ghostwriting Services For School, Essay On Tonga In Hindi.