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Reverse osmosis technology for water treatment: State of the art review
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.
... However, accurately determining pore size has remained a significant challenge for decades, complicating filtration control and limiting the ability to precisely tailor membranes to specific process requirements. Well-established methods for membrane characterization include estimating molecular weight cutoff (MWCO), bubble point testing, water flux measurement, solute rejection testing, mercury porosimetry, vapor-liquid equilibrium, gas-liquid equilibrium or permporometry, solid-liquid equilibrium or thermoporometry, and microscopic techniques [177]. At the same time, the demand for technologies capable of the increasingly precise removal of small contaminants continues to grow, putting pressure on membrane manufacturers and driving the need for the development of new measurement methods to keep pace with advancements in filtration engineering. ...
... Meanwhile, energy losses in ERDs are due to their efficiency, which never reaches 100% due to mechanical and hydraulic phenomena. The simplest model describing the transport of mass, salts, and solvents through RO membranes is the Kedem-Katchalsky equation [177]. ...
... The formation of biofilm occurs when microorganisms adhere to the membrane surface and grow in the presence of a polysaccharide matrix [195]. To inhibit the growth of microorganisms, chlorine is often used, but RO membranes are sensitive to its free form, while they show much higher tolerance to chloramines-this is why chloramines are commonly used to limit microbial growth [177]. A key method to extend membrane life and reduce contamination is proper pretreatment of the feed liquid (e.g., leachate from landfills). ...
Nitrogen pollution poses significant environmental challenges, contributing to eutrophication, soil acidification, and greenhouse gas emissions. This study explores advanced methods for nitrogen removal and recovery from municipal and industrial wastewater, with a focus on biological, chemical, and physical processes. Key processes, such as nitrification–denitrification and emerging technologies like shortcut nitrogen pathways, were analyzed for their efficiency, cost-effectiveness, and environmental benefits. This review highlights the integration of innovative techniques, including membrane systems and ammonia stripping, with traditional approaches to enhance nitrogen management. Emphasis is placed on optimizing operational conditions, such as pH, temperature, and carbon-to-nitrogen ratios, to achieve high removal rates while minimizing energy consumption and environmental impact. These findings underline the critical role of interdisciplinary strategies in addressing the challenges of nitrogen pollution and promoting sustainable wastewater management.
... The use of low hydraulic resistance membranes and pressure recovery systems can reduce energy requirements by 15-25%, representing a significant opportunity for energy optimisation. However, membrane filtration is associated with high investment costs and the need for frequent membrane servicing, which is a significant limitation to its widespread use [73,80]. ...
... Emerging solutions such as nextgeneration membrane filtration, advanced oxidation processes (AOPs), artificial intelligence (AI)-driven process automation, and water recycling technologies are transforming the industry. These advancements reduce energy consumption, enhance treatment effectiveness, and lower the environmental footprint of WTPs [80,81]. However, despite their potential, economic, regulatory, and technical barriers continue to hinder widespread implementation. ...
... Adapting this infrastructure to new technologies, such as intelligent management systems or advanced filtration processes, is a challenge technically and in terms of cost [90]. For example, the integration of modern membranes requires not only the installation of new equipment, but also the modification of water transport and storage systems, which generates additional costs and increases implementation time [80]. Furthermore, the implementation of modern technologies requires skilled engineering and technical staff who are able to operate and service the advanced equipment. ...
The energy efficiency of water treatment plants (WTPs) plays a key role in the sustainable management of water resources. In the face of increasing water demand, climate change, and increasingly stringent environmental regulations, optimising the energy consumption of treatment processes is becoming a priority for water system operators and decision-makers alike. Water treatment plants, depending on the type of water source served (groundwater, infiltration, surface water), vary considerably in terms of their technological design, which directly affects their energy efficiency and operating costs. According to the International Water Association, the water sector accounts for approximately 4% of global electricity consumption, a significant proportion of which is consumed by water treatment and distribution processes. Electricity is used in many process steps, such as water pumping, aeration, filtration, disinfection, and filter flushing. The energy consumption of a System for Upgrading Water (SUW) depends not only on the quality of taken raw water, but also on the size of the station, used technologies, and operation organisation. This study shows that implementing high-efficiency pumping systems and AI-based optimisation can reduce energy consumption in WTPs by 20–30%. The introduction of membrane filtration in surface water plants has demonstrated a reduction in energy use by up to 50%, while the use of biogas from sludge treatment has cut external energy demand by 15–25%. The results emphasise the potential to reduce CO2 emissions by 10–20% compared to conventional treatment methods. However, achieving significant reductions in energy consumption in SUW requires a comprehensive understanding of the diversity of water facilities, technological processes, and specific energy requirements.
... Together with the introduction of thin-film composite (TFC) polyamide (PA) membranes that increased permeate flux and improved rejection [4], RO energy consumption decreased dramatically over the years, to values that nowadays are only two or three times thermodynamic minimum, making RO currently the most energy-efficient desalination method [5]. Besides production of water for human consumption and agriculture, RO technology has many different applications, such as in food processing, and use in the pharmaceutical, textile and paper industries [6]. ...
... Among those models are solution-diffusion models, which assume constant pressure and concentration gradients as the only driving force in the process, pore-flow models based on the pressure difference as driving force, and molecular dynamics simulations that address the mechanism on the molecular level, thereby taking the membrane composition also into account. In addition, irreversible thermodynamics models use a phenomenological approach to describe membrane transport [6,10,11]. ...
We present theory for ion and water transport through reverse osmosis membranes based on a Maxwell-Stefan framework combined with hydrodynamic theory for the reduced motion of particles in thin pores. We include all driving forces and frictions both on the fluid (water), and on the ions, including ion-fluid friction as well as ion-wall friction. By including the acid-base character of the carbonic acid system, the boric acid system, HO/OH, and the membrane charge, we locally determine pH and thus the effective charge of the membrane as well as the dissociation degree of boric acid. We present calculation results for a dead end experiment with fixed feed concentration, where effluent composition is a self-consistent function of fluxes through the membrane. Comparison with experimental results from literature for fluid flow vs. pressure, and for salt and boron rejection, shows that theory agrees well with data. Our model is based on realistic assumptions for the effective sizes of the ions and for the diameter of the RO membrane pore in the polyamide toplayer (0.75 nm).
... On the market, spiral wound and hollow fiber modules are most common. The cost of reverse osmosis systems remains a major concern, both in terms of energy consumption and membrane replacement [14][15][16][17] . Forward osmosis (FO): The Forward Osmosis (FO) water-purification technology could be used to remove inorganic, organic, and biological contaminants. ...
... Forward osmosis (FO): The Forward Osmosis (FO) water-purification technology could be used to remove inorganic, organic, and biological contaminants. Engineered FO processes rely on osmosis, which is the movement of water from higher to lower water potentials [13][14][15][16][17][18] . Ultraviolet (UV) purifiers: It was discovered in 1887 that UV light has germicidal properties. ...
Water is life for all but the global problem of water pollution requires a continuous evaluation of water resource policy. Day by day water pollution increases due to rapid industrial growth and create demand drinking water. In industrial effluent, high levels of radioactive and hazardous chemicals harm living organisms. Water supply, rivers, lakes, and oceans worldwide are affected. Water pollution is a problem facing both developed and developing countries. Therefore, it has an adverse effect on the natural environment as well as human health. The domestic water purifier market in India has expanded significantly over the last decade, propelled by growing awareness of waterborne diseases and increased disposable incomes among consumers. This study reviews the current state of the domestic water purifier sector, identifies key growth factors, and anticipates future trends. Advances in technology and a governmental focus on providing clean drinking water suggest that the market is set for considerable growth. The paper also highlights potential challenges and opportunities for stakeholders within this expanding industry.
... 15,16,31−35 It should be noted that Reaction 1 is mainly considered for maritime applications 36 due to the continuous availability of water, utilizing reverse osmosis. 37,38 Reverse osmosis enables the conversion of brine to fresh water during the transport period, and hence, reducing the fuel weight requirement at the start of transport. 8,36,39,40 As NaBH 4 reacts with water, an aqueous mixture of NaBH 4 and NaB(OH) 4 is formed. ...
... [10][11][12] As a result, their use must be carefully controlled and treated before being released into the environment. Various methods have been used for dye removals including degradation, coagulation, photocatalysis, flocculation, hydrogen peroxide, oxidation, irradiation, ion exchange, reverse osmosis, advanced oxidation, membrane filtration, precipitation, etc. [13][14][15][16] Among these methods, adsorption has shown a good technique compared to other techniques due to its simplicity, high efficiency in dye removal, low energy requirements, and the availability of various adsorbents. Additionally, it offers advantages such as effective regeneration and the ability to reuse the adsorbent. ...
Cationic dyes, such as methylene blue (MB) and brilliant yellow (BY), cause significant environ-mental pollution. Most common dye adsorbents are difficult to produce and are not environ-mentally friendly. In recent years, a number of scientific studies have focused on thepreparation and use of grafted hydroxyapatite (HAp). In this context, we prepared HAp usingAlgerian natural phosphate and grafted it with sodium metasilicate (MNP-MSi) via the precipita-tion method to precisely improve certain physico-chemical properties to increase the adsorptioncapacity for MB and BY dye. The successful synthesis of MNP-MSi was evaluated through mul-tiple techniques including X-ray diffraction (XRD), Scanning electron microscopy coupled withenergy dispersive X-ray spectrometry(SEM/EDS), Fourier Transforms Infrared spectroscopy (FTIR),and thermogravimetric analysis (TGA). Batch adsorption experiments were conducted, and theinfluence of experimental parameters such as contact time (up to equilibrium), adsorbent dose(1–6 g/L), pH ((2–9)±0.2) and initial dye concentration (10 and 200 mg/L) was studied. The opti-mum conditions were pH 7 ± 0.2 and adsorbent dose of 1 g/L for BY and 2 g/L for MB, withmaximum adsorption percentages reaching 100.0% for BY and 98.7% for MB at 10 mg/L. For200 mg/L, the adsorption efficiency declined to 98.13% and 86.19% for BY and MB, respectively.Kinetic data revealed that the driving force behind the adsorption process in both systemscould be explained by a pseudo-second- order mechanism. The equilibrium details for BY werewell described by the Freundlich isotherm, whereas the adsorption equilibrium data for MBobeyed the Langmuir model. The regeneration study demonstrated that MNP-MSi2 could beeffectively reused for removing MB and BY dyes for at least four successive adsorption–desorp-tion cycles, using NaOH and HCl as desorption agents.
(PDF) Removal of methylene blue and brilliant yellow from aqueous solutions using sodium metasilicate modified hydroxyapatite derived from Algerian phosphate rocks. Available from: https://www.researchgate.net/publication/389835981_Removal_of_methylene_blue_and_brilliant_yellow_from_aqueous_solutions_using_sodium_metasilicate_modified_hydroxyapatite_derived_from_Algerian_phosphate_rocks?origin=mail&uploadChannel=re390&reqAcc=Souad-Feddane&useStoredCopy=0 [accessed Mar 23 2025].
... 15 On the other hand, RO has a major drawback because of the high external pressure needed (> 50 bar) to force water through the semipermeable membrane, which promotes the interaction of foulants (organic, inorganic, bio) with the membrane surface, thus causing an accelerated fouling of the membrane. 16 Therefore, there is a strong motivation to explore and conduct research on new membrane-based technologies with minimal energy consumption minimizing membrane fouling problems. ...
This study investigates the potential of using low-cost commercial superabsorbent polymers (SAPs) as draw agents in a hydrogel-driven forward osmosis (FO) desalination process. Different types of commercial SAPs were tested,...
... To effectively remove pollutants from wastewater, various techniques have been established. OF these, coagulation [10], sedimentation [11], filtration [12], chemical purification [13], reverse osmosis [14], photocatalytic degradation [15,16], ion exchange [17], biological treatments [18] and other techniques were noted for water remediation [1]. The selection of water treatment techniques depends on flexibility and the lowest economic cost, so adsorption is considered an extremely widely used technique because it is a simple and inexpensive method [19]. ...
Water is one of the vital needs of life. However, due to rapid industrialization, urbanization and lack of awareness, the world population now facing the threat of water shortage. To ensure that future living conditions are preserved, it is crucial to reduce water pollution and protect the ecosystem. Zinc oxide- reduced graphene oxide (ZnO-RGO) nanocomposite is used in this study as an adsorbent for the adsorption of methylene blue (MB) dye from an aqueous solution. An easy strategy was used for the synthesis of reduced graphene oxide nanoparticles (RGO), Zinc oxide nanoparticles (ZnO) and ZnO-RGO nanocomposite. The synthesis of reduced graphene oxide (RGO) was accomplished through the exothermic reaction of a modified Hummer's method. In a novel approach, zinc oxide nanoparticles (ZnO NPs) were synthesized using the green Leidenfrost technique. This study presents a comparative investigation of ZnO-RGO nanocomposite synthesis employing both green and chemical methods. Three distinct approaches were utilized to prepare the ZnO-RGO nanocomposite: (1) the innovative Leidenfrost green method for composite A1, (2) a chemical precipitation method for composite A2, and (3) a physical mixing sonication method for composite A3. This research marks the first application of the Leidenfrost technique in the synthesis of ZnO-RGO nanocomposites, contributing to the growing body of knowledge in this field. X-ray diffraction (XRD), Burnauer-Emmett-Teller (BET), Fourier transform infrared (FTIR), Zeta potential, transmittance electron microscope (TEM) and scanning electron microscope (SEM) analyses are conducted for synthesized sample characterization. Comparing the XRD patterns of the three synthesis methods, it is notable that the intensity peaks of composite A3 were the highest when ZnO was synthesized using a green method, indicating a higher degree of crystallinity. FTIR analysis approves that combining ZnO with RGO affects the functional groups of the three nanocomposite surfaces. The SEM analysis shows ZnO NPs and RGO sheets are incorporated together. In the case of A1 composite sharp angles make a flower shape was observed due to the unique synthesizing method. The surface area for A2 composite is the highest (7.29 m²/g) compared with A1 (2.91 m²/g) and A3(1.90 m²/g). A comparison study is made among the three nanocomposites for MB dye removal. The effect of adsorbent dose, pH, contact time and initial dye concentration on dye adsorption has been studied. The results show that A1 and A2 nanocomposites removed 85.5 and 87.5% of MB at the optimum adsorbent dose of 0.15 g/100 ml at pH8 and A3 removed 95% of MB at the optimum dose of 0.1 g/100 ml at pH 2. All three composites exhibited adherence to the Langmuir isotherm model, with correlation coefficients (R²) of 0.9858, 0.9904, and 0.9959 for A1, A2, and A3, respectively. Kinetic study results demonstrated that the pseudo-second-order model best described the adsorption process for all three composites, yielding R² values of 0.9998, 0.9988, and 1.0000 for A1, A2, and A3, respectively. The A3 nanocomposite shows the highest adsorption capacity (104.5 mg/g) compared to the other composites (87.7 and 97.5 mg/g for A1 and A2, respectively). Desorption experiments revealed that the dye removal percentages varied with the ratio of the ethanol–water mixture used. Absolute ethanol achieved a 90% removal compared with 1:1 and 1:2 aqueous ethanol solutions (87.5% and 80%, respectively).
... The most widely employed desalination technology is reverse osmosis (RO) due to its propensity to provide a high quantity and quality of freshwater with modest operating costs [1,3]. RO is a pressure-driven filtration process whereby all the smallest contaminants and dissolved constituents can be rejected over a semi-permeable membrane by applying hydraulic pressure, which results in highly purified water production [2,4]. Spiral wound membrane modules (SWMs) are the predominant commercial configuration for the RO process [5]. ...
Reverse osmosis (RO) filtration performance is heavily influenced by the design of the feed spacer. Spacer design impacts hydrodynamic patterns within the system, affecting water production and concentration polarization. Two spacer designs, namely pillar (P) and standard (S), were investigated to improve the performance of a commercially available spacer design (C) in the RO process. Two approaches were employed to evaluate spacer performance. First, direct numerical simulation (DNS) was utilized to fundamentally understand the hydrodynamics generated by each spacer design. Second, laboratory RO experiments were conducted to confirm the simulation results. The P and S spacers induced higher flow velocity and vorticity than the C spacer, as confirmed by simulations and experiments. Reduced dead zones were also demonstrated using P and S spacers. However, the standard spacer design exhibited a clear advantage in promoting more efficient mixing within the filtration channels. This enhanced mixing substantially reduced salt concentration at the membrane surface, improving the filtration performance. In agreement with the permeation velocity computation, the S spacer achieved the highest improvement (13%) in both flux yield and specific flux relative to the C spacer. This finding confirms the S spacer’s ability to enhance RO performance while reducing energy consumption.
... Osmosis is a naturally occurring phenomenon where water molecules migrate spontaneously from a solution with low osmotic pressure to a solution with high osmotic pressure, facilitated by a semi-permeable membrane [56][57][58]. The semi-permeable membrane allows only water molecules to pass through, while selectively blocking the passage of solutes. ...
... Currently, the microbiological assessments of bottled waters are projected to include the determination of the microbial count, identification of the pathogenic flora and the investigation of the presence of specific indicators of human or environmental contamination [15]. Reverse Osmosis (RO) is a water purification technique that it basically depends on the use of semipermeable membranes for water filtration [16][17][18]. It can physically separate and remove the unwanted components such as dissolved solids, bacteria, viruses, and heavy metals from the water [19][20][21][22]. ...
Background and aims. Access to clean and safe water is essential for human life. Among the quality control requirements of drinkable water are the microbiological monitoring tests to prevent any microbial contamination. Bottled water is generally considered to be safe for use by people. However, several reports have reported that bottled water does not always meet the accepted standards. House hold Reverse Osmosis (RO) stations are commonly used in houses which purified the supply water using membrane filters, it has high efficiency in removing dissolved salts, chemicals, impurities and microorganisms from the water. This study aimed to assess the microbiological quality of RO water samples and some domestic bottled waters marketed in Tripoli-Libya. Methods. About 9 samples of different bottled drinking water and 18 samples of RO drinking water were collected from different parts in Tripoli. Results. The microbiological analysis tests of this study showed that the total bacterial counts of bottled waters and one sample of RO water were below 10 CFU/100 ml. A total of 16 RO samples had a total of the bacterial count in the range between 10 and 300,000 CFU/100 ml and one sample was found with a bacterial count of more than 300,000 CFU/100 ml. However, total coliform bacteria, yeast and mold were not detected in all bottled and RO water samples. Conclusion. The tested domestic bottled waters sold in markets and shops in Tripoli have bacteriological contents within the accepted ranges based on WHO standards, whereas almost all the RO samples have high bacterial count that can be risky to human health. Accordingly, the public should be aware of the proper use of RO stations and monitoring the validity of filters in order to be efficient to produce safe water that is free of microbial and chemical contamination.
... Precedence: Some examples for current methods for wastewater treatments include reverse osmosis, [16] ultra violet (UV) photolysis/photocatalysis, [17] activated carbon adsorption, [18] and membrane filtration. [19] Nevertheless, the development of low cost and energy efficient technologies for sustainable water purification is still a pressing issue that needs to meet the demands of billions of people across the globe. ...
Water pollution is a critical environmental issue affecting ecosystems and human health worldwide. Contaminants such as heavy metals, dyes, antibiotics, and microplastics enter water bodies from the disposals of industrial, agricultural, and domestic waste. The development of new and advanced technologies for addressing water remediation has turned out to be a dire need. Protein‐inorganic hybrid materials have emerged as innovative solutions for water remediation, leveraging the unique properties of both the proteins and the inorganic components. These hybrid materials connect the biocompatibility and specificity of proteins with that of the structural stability and catalytic capability of the inorganic frameworks. In recent times, protein inorganic hybrids are gaining importance in water remediation due to their ease of synthesis and chemical modification, stability, biocompatibility and biodegradability. This article brings out the recent advancements in the development of two major kinds of protein inorganic hybrid materials, viz., metal phosphate nanoflowers and gels in the context of water purification. The effect of major factors, like, morphology, porosity, pore size and nature, surface area, and the nature of the composite were systematically compared and analyzed to make it beneficial for future researchers in the development of such hybrid materials for water remediation in a sustainable manner. For this, the article addresses the current trends and draws conclusions on future perspectives to support the topic on providing clean and potable water for everyone on the globe.
... The abovementioned values take into account both the RO plant itself and the footprint of auxiliaries (e.g., pumping system, pretreatment system, etc.). Estimated capital expenditures are 150-455 USD/m 3 [42]. ...
Green hydrogen, produced by water electrolysis using renewable energy sources (RES), is an emerging technology that aligns with sustainable development goals and efforts to address climate change. In addition to energy, electrolyzers require ultrapure water to operate. Although seawater is abundant on the Earth, it must be desalinated and further purified to meet the electrolyzer’s feeding water quality requirements. This paper reviews seawater purification processes for electrolysis. Three mature and commercially available desalination technologies (reverse osmosis, multiple-effect distillation, and multi-stage flash) were examined in terms of working principles, performance parameters, produced water quality, footprint, and capital and operating expenditures. Additionally, pretreatment and post-treatment techniques were explored, and the brine management methods were investigated. The findings of this study can help guide the selection and design of water treatment systems for electrolysis.
... Even though numerous RO plants have been built already, more research is still required to improve the membrane flux along with high salt rejection (Megha et al., 2024). In this aspect, membranes made of Thin film composite (TFC) have been the subject of numerous reviews that address various such features (Fritzmann et al., 2007;Kang & Cao, 2012;Li & Wang, 2010;Malaeb & Ayoub, 2011). The majority of these studies were focused on either developing novel monomers and additives or improving the fabrication procedures for membranes. ...
Desalination is the most promising technology to resolve present water scarcity issues and improvement is required to increase its productivity and various other drawbacks including lower water flux, membrane fouling, and high-energy requirements. Currently available desalination membranes exhibits a water flux of 18–34 L/m².h. Modification of the existing membranes can enhance its performance and thereby makes it efficient for desalination. In this investigation, introduction of Polyvinyl pyrrolidone was aimed to enhance the permeability of the Polysulfone membrane, given that the membrane’s water flux is predominantly influenced by its porosity. Further modification of the membrane was done by adding functionalized multi-walled carbon nanotubes onto the polyamide layer over the polysulfone membrane to improve the salt removal efficiency. The fabricated membranes were characterized by its swelling, porosity, water uptake, surface roughness, contact angle, morphology and surface chemistry. The performance of the fabricated membrane for desalination was evaluated using a cross flow filtration experimental setup. The characterization studies confirmed the modification of hydrophobic polysulphone membrane to hydrophilic by the addition of functionalised multi-walled carbon nanotubes (MWCNTs). The findings demonstrated that the membrane with 0.01% w/v of MWCNTs exhibited enhanced water flux at 42 L/m².h with a salt rejection of 92%. The performance of the used membrane was retained by conducting regeneration study using acid cleaning. This study will be helpful for water managers to come out with a better method to fabricate membranes for desalination.
... Thus, an NF membranewith hydrophilic surfaces that prevent the formation of organic layers and maintains high permeation flux of the membrane is highly desired. Further, small charged particles especially monovalent ions are known to be separated by 99.5% due to the high efficiency of reverse osmosis (RO) [45]. It has been found that the combination of NF and RO technologies have been successful in the removal of 98% of contaminants from wastewater such as dissolved solids, metals, and dyes. ...
In order to meet the demand for portable water and replenish depleting water resources caused by industrialization, urbanization, and population growth; wastewater purification has become crucial. Emerging contaminants (ECs), which include organic dyes, pesticides, pharmaceutical drugs, polyaromatic compounds, heavy metal ions, and fertilizers, among others, have caused significant disruptions to environmental balance and severe health complications. As a result, considerable effort has been devoted to the development of technologies that eliminate wastewater from effluents via adsorption, photocatalysis, and other means. However, considering the economic and environmental implications of the adopted technologies, green technology has gained significant attention owing to their eco-friendly approaches, cost-effectiveness, avoiding use of toxic and harmful chemicals and production of less-toxic by-products. Currently green-synthesized nanomaterials have seen tremendous growth in emerging as sustainable nanoadsorbents, nanocatalysts for the removal of the emerging contaminants from wastewater in highly efficient and eco-friendly manner. Thus, this review presents an overview of the various techniques utilized in wastewater treatment with a particular emphasis on the production and application of environmentally friendly transition metal/metal oxide nanoparticles as sustainable tools in wastewater treatment technology. This article also discusses the limitations and future potential of using green-synthesized transition metal/metal oxide based nanoparticles in advancing the technology on a broad scale.
... Since salt removal efficiency depends on the treatment type [26], the operating conditions, the bacterial communities involved [27], and their adaptation to salinity [28][29][30], salt removal in WWTPs might require advanced treatments, which are usually lacking in WTTPs located in small and medium size cities [4,31]. Moreover, treatments like reverse osmosis or membrane systems are costly, energy-intensive, and produce by-products (e.g., brines), limiting their adoption [32,33]. Consequently, most urban WWTPs rely on indirect salt removal processes (e.g., conventional physicochemical and biological reactions) and rarely monitor salinity variations and their effects on microbial communities [34,35]. ...
... RO membranes are exceptionally proficient at decreasing the SAR (sodium adsorption ratio) of water by effectively removing both monovalent and divalent ions, such as sodium, calcium, and magnesium [39,40]. The compact pore structure of RO membranes hinders the movement of ions, leading to a noteworthy decrease in SAR values [41]. ...
In this work, the performance of a Reverse Osmosis (RO) process using different types of reverse osmosis (RO) and nanofiltration (NF) membranes is evaluated for brackish water desalination for producing irrigation-grade water. The proposed desalination system is a single-stage system, where three types of RO and two NF membranes were examined. The different desalination systems were simulated using ROSA72 software. In order to validate the theoretical model, the results obtained from the simulation were compared to those obtained from the experiment conducted in this work. The El-Moghra aquifer of Egypt is considered the test bed due to a considerable amount of data being available for this aquifer. The El-Moghra aquifer has 79 wells, and the available water data, when checked against several quality parameters, show that none of the investigated wells are suitable for direct irrigation without treatment due to problems of salinity, the sodium adsorption ratio, and low water quality according to the irrigation water quality index values. The obtained results show that nanofiltration membranes exhibited superior energy efficiency compared to reverse osmosis membranes. However, what sets the nanofiltration membranes apart is their ability to elevate water quality in 89.9% of the total investigated wells to an acceptable level for agricultural purposes. This underscores the nanofiltration membranes as a highly effective alternative to reverse osmosis membranes, demonstrating the capability to produce water suitable for irrigation while concurrently reducing operational costs due to the lower energy consumption in nanofiltration-based systems.
... Thermal desalination involves utilizing direct or indirect thermal energy to separate freshwater from saline water. On the other hand, RO desalination utilizes a semi-permeable membrane to separate water from salt [21]. While RO has advantages in terms of energy consumption, it faces challenges in membrane maintenance. ...
This paper examines the viability of introducing solar thermal desalination technology as a means to supplement existing water production methods in the Republic of South Africa (RSA). The study provides an overview of the current state of desalination technology in the country. A key aspect of this study involves comparing the RSA with the Middle East and North Africa (MENA) region, using publicly available studies and reports. The focus of this comparison is to highlight the potential implementation of large-scale solar desalination in the RSA by evaluating the respective resources and environmental data that directly impact the input and output of a thermal desalination system. The study comparatively analyzes the environmental conditions and seawater salinity of the RSA and the MENA region. The RSA receives a higher solar irradiation range of 4.5–6.5 kWh/m², whereas the MENA region experiences a range of 3.5–5.5 kWh/m². Additionally, the salinity of the RSA’s seawater ranges between 35 and 35.5 parts per thousand, which is lower than the MENA region’s range of 36–40 parts per thousand. The study also reviews and proposes the adoption of an emerging thermal desalination method that has been successfully tested in the MENA region and other countries, based on its performance.
... Various biological and physicochemical methods have been developed to remove these organic toxic compounds from industrial wastewater, aiming to minimize their environmental consequences. The biological methods include anaerobic and aerobic processes [3], precipitation [4], chemical oxidation [5], Flocculation-coagulation [6], ionexchange [7], membrane filtration [8], photocatalytic degradation [9], and adsorption [10]. However, the most of organic dyes are difficult to be remove using conventional biological and physicochemical processes since these compounds are stable against the oxide agents, resist biodegradation and light [11]. ...
This study investigates the adsorption of Brilliant Scarlet 3r dye (BS 3r) onto corn silk (CK), an agricultural waste, in a neutral medium. The characteristics of corn silk as an adsorbent were analyzed using Fourier transform infrared spectroscopy (FTIR) and Atomic force microscopy (AFM). Batch adsorption experiments were conducted to examine the effects of corn silk weight, initial BS 3r concentration, adsorption period, adsorption temperature, and pH of the medium on the adsorption process. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms models were used to represented the equilibrium experimental date, the obtained values of correlation coefficient R2 indicated that the adsorption followed the Langmuir isotherm. The kinetics analysis results showed that the adsorption of Brilliant Scarlet 3r dye (BS 3r) onto corn silk followed the pseudo second-order model (PSOM), indicating its suitability for describing the adsorption kinetics. Thermodynamic parameters, including ∆G˚, ∆H˚, and ∆S˚, indicated that the adsorption process of BS 3r dye onto corn silk was spontaneous and exothermic in nature.
Neutral and small molecules such as boric acid（H 3 BO 3 ）are poorly rejected by state-of-the-art reverse osmosis（RO）and nanofiltration（NF）membranes. Therefore, the objective of this study was to investigate physico-chemical properties of active layers controlling the H 3 BO 3 rejection by polyamide composite RO/NF membranes. To achieve the this objective, we measured the concentration of deprotonated carboxy group（R-COO －）of polyamide active layer of eight commercial RO/NF membranes by probing R-COO － with the Ag ＋ at pH 6.0 and 10.0 and quantifying the Ag ＋ using a Rutherford backscattering spectrometer. We also characterized polyamide active layers using thermal gravimetric analysis. These physico-chemical properties of RO/NF membranes were then used to investigate the relationship with water/H 3 BO 3 transport parameters obtained by modeling experimental data using the solution-diffusion model allowing for the existence of unhindered advection through nano-scale imperfections. It was found that the H 3 BO 3 permeability and water selectivity of RO/NF membranes were most strongly related to the temperature at which 20 ％ weight loss occurs, an indicator of molecular weight of polyamide active layers. Positive correlation, although weak, was also observed with the concentration of R-COO － at pH 6.0. These results indicate that aggregate pores in polyamide active layers play an important role in water and H 3 BO 3 permeation through RO/NF membranes.
New energy materials and technologies are developing rapidly, and the sales of electric vehicles are increasing significantly. The cathode material is the core of electric vehicle batteries. The production of electrode precursors generates a large amount of wastewater. Power lithium-ion battery precursor wastewater is highly toxic to the ecosystem and human health. For wastewater that cannot be treated biologically and for resource recovery, membrane technology demonstrates superior performance.The objective of this paper is to comprehensively organize and summarize the role of membrane processes in treating precursor wastewater from power lithium-ion batteries for water recovery and resource utilization. Firstly, by analyzing the sources and characteristics of various precursor wastewater and understanding the fundamentals of membrane technologies, this study aims to summarize the ability of different membrane processes to treat contaminants in precursor wastewater from power lithium-ion battery production. The performance of membrane filtration in removing heavy metals, recovering valuable salts, and water recycling is also discussed. Furthermore, the article emphasizes membrane fouling issues and reviews various strategies for mitigating contamination. Ultimately, the possible pathways for the resource reuse of power lithium-ion battery precursor wastewater were also proposed.
Water pollution caused by pharmaceuticals is a major concern that arises from various human actions such as industrial, medical, and domestic use. The presence of these pollutants in water bodies can lead to the deterioration of water quality, which in turn can affect human health. Therefore, it is essential to adopt new techniques to remove these pollutants from water. One effective process for eliminating pharmaceutical pollutants from water is the Fenton-based advanced oxidation process (AOP). Over the past few decades, iron-based catalysts have gained significant attention as efficient Fenton catalysts for pharmaceutical environmental applications due to their high catalytic activity, redox, and magnetic properties. This chapter aims to provide a summary of the treatment of wastewater produced by pharmaceutical industries using various Fe-based catalysts through the Fenton oxidation system. The integration and combination of the Fenton system with other AOPs, such as photo-Fenton (PF), sono-Fenton (SF), electro-Fenton (EF), sono-electro-Fenton (SEF), sonophoto-Fenton (SPF), and photo-electro-Fenton (PEF) have also been discussed and evaluated to achieve high-performance elimination of pharmaceutical pollutants. The chapter concludes with final remarks on the research challenges and prospects in this field.
Many nations have poor wastewater infrastructure and untreated discharges. Due to water constraints, pollution and the need for sustainable solutions, wastewater issues must be addressed for environmental and public health concerns. Since green energy is in demand, biogas is a viable alternative. Methane is the major component of biogas from organic waste anaerobic digestion. Impurities like carbon dioxide and hydrogen sulphide impede its clean energy application. Membrane technique selectively removes contaminants and increases gas calorific value in biogas. Membrane technology can clean wastewater and upgrade biogas, solving environmental issues and generating sustainable energy. This chapter shows how new membrane materials and design impact performance, durability and cost. This thorough summary of membrane technology and its revolution in wastewater treatment and renewable energy is provided. Sustainable development is becoming increasingly vital as economic growth and living standards balance. Urbanization and industrial expansion increase water use, pollution and wastewater discharge annually. Polluted wastewater can affect animal habitats in natural streams or soils. For environmentally friendly wastewater treatment and biogas upgrading, membrane technology is crucial. Global concerns about water shortages, pollution and renewable energy sources have raised demand for creative technology that decreases environmental effect and provides resources. In this chapter, membrane technology’s intricate role in wastewater treatment and biogas upgrading is addressed, along with recent improvements and fascinating potential.
Herein, an ultrasonication approach was used to anchor In2S3 quantum dots (QDs) onto oxygen-doped graphitic carbon nitride (O@g-C3N4), resulting in a novel heterojunction catalyst. Characterization techniques validated the successful incorporation...
The application of hollow fiber membranes is one of the excellent processes to treat oily wastewater and wetland water. Treating oily wastewater and wetland water is a significant challenge and reported expensive. These wastes generally come from due the expansion of massive industries and human activities these days. This review discusses the critical ways of membrane hollow fiber application in treating oily wastewater as well as wetland water. It is also reported in literature that there is mostly organic contaminant accommodated in oily wastewater and wetland water. Due to that, the application of hollow fiber is the best way as a removal organic contaminant in oily wastewater as well as wetland water. Apart from that, the conventional and advanced methods are also well explained within this review followed by detail treatments, application, and performance of this hollow fiber membrane application. To achieve the best completed outcome of pollutants removal, several applications relate to other processes before contacting to hollow fiber membranes. The integration between conventional and advanced membrane technology in oily wastewater and wetland treatment is also well explained. The important factors in the fabrication and application of hollow fiber membrane depend on membrane materials and filtration processes. It means that the selection between membrane materials and final processes to choose are depending on the urgency, source of pollutants, and intended use.
The impact of ion competition on nitrate removal from contaminated groundwater using membrane-based bioelectrochemical systems is investigated.
In recent years, accelerated growth of industries is hand to hand with the economic growth of developing countries. Industrial development positively impacts the living standards and economic sector, but also greater strains on available resources and severe threat to environment. Among all the industrial wastes, liquid discharge is the most dreadful concern at present. Increasingly stringent government water quality policies enhanced the necessity of proper effluent treatment technology with cost effectiveness and consistent operations. There are many methods for wastewater treatment but from last few decades, substantial use of reverse osmosis (RO) membrane for water recovery from effluent streams has strengthen the demand of different approaches for the desired efficiency of salt removal and elevated water recycle ratio. In this paper to overcome environmental problems, an effort has been made for advanced treatment of pharmaceutical and tyre industrial wastewater. The paper shows that membrane M1 when exposed to 1000 mg/l of Sodium Chloride shows the rejection of 97.46% with water flux of 33.73 (l/m2hr). Additionally, membrane M2 when exposed to 1000 mg/l of Sodium Chloride shows the rejection of 96.85% with water flux of 38.92 (l/m2hr). The results obtained highlights that the separation in RO resulted in appreciable removal of TDS from M1 are 88.31 % while from M2 is 89.23 % in case of pharmaceutical wastewater. Moreover, the performance of TDS separation in M1 is 86.69 % whilst from M2 is 87.27 % is main subject of interest in case of tyre wastewater. Based on the results obtained, it can be concluded that the RO has been effective in the reduction of COD, BOD with complete TSS removal.
Nitrate pollution from agricultural production is a major threat to water resources worldwide. This study quantifies the consequences of groundwater nitrate pollution for the drinking water supply sector by estimating the effect of groundwater nitrate pollution on the costs of water utilities. In doing so, we contribute to the estimation of the external costs of agricultural nonpoint pollution associated with drinking water supply. Empirical evidence is based on fixed effects regressions using large panel data sets on water supply companies and groundwater sampling sites in Germany. Local nitrate pollution at the abstraction plant is approximated using spatial interpolation. Our findings reveal that water suppliers incur substantial costs through groundwater nitrate pollution in terms of increased treatment and total costs. The estimated cost elasticities range from 0.048 to 0.052 for treatment costs and up to 0.019 for total costs. For an average firm, these estimates imply annual increases in treatment and total costs of €39,000 and €116,000, respectively, for a 10 milligrams per liter increase in groundwater nitrate concentrations.
Amidst a global water crisis, Jordan is an example of extreme water scarcity. With one of the world’s lowest per capita freshwater availability, Jordan’s growing population and limited resources create a dangerous balance. This research paper investigates into the vital role of renewable energy in addressing Jordan’s water woes and proposes a sustainable path for the future. Through a comprehensive case study, integrating renewable energy and water desalination in arid regions represents a promising pathway for sustainable water management and environmental conservation. By harnessing abundant renewable resources, arid regions can address their pressing water needs, mitigate climate change, and reduce dependence on non-renewable energy sources. Overcoming economic barriers and optimizing technology will be crucial in fully unlocking the potential of this innovative approach for a water-secure and environmentally conscious future.
This paper describes the treatment of chemical mechanical polishing (CMP) wastewater from a semiconductor plant through membrane-based ultrafiltration (UF) and reverse osmosis (RO) processes to improve the removal efficiency under different water recovery and to determine the possible mechanisms of membrane blocking and rejection. UF pretreatment led to 42.1-46.9% conductivity, 98.1-99.4% turbidity, and 4.5-24.5% total organic carbon (TOC) removal. These contaminants were almost completely rejected after performing subsequent RO processing: the values of the conductivity, turbidity, and TOC were reduced to 6 μS/cm, 0.01 NTU, and 1.6 mg/L, respectively. The water quality of the permeates after UF or RO membrane filtration could meet the water reuse standards for tap water, cooling water, boiler water, and the feed for a water purification machine. The variation with time of the permeate flux for the UF process was fitted to the Hermia model to examine the possible blocking mechanisms during the filtration process. The possible rejection mechanisms of the membrane processes are discussed herein in terms of the water quality variation during the membrane-based separation processes.
The membrane and spiral-wound elements used for seawater desalination continue to evolve, particularly in regards to lowering energy costs. Most recently, high area elements and ultra low pressure seawater reverse osmosis (SWRO) elements have come onto the market. Laboratory and pilot testing of these elements demonstrate that they can achieve both high rejection and low pressure operation. Use of these high performance SWRO products is a challenge, however. Detailed analysis indicates that the higher permeability membranes have a greater flux imbalance in the process, but there are ways to take advantage of these capabilities with proper system design. An example of the use of high area seawater membranes will be presented. It shows that significant capital savings can be achieved. Using high area elements to run at lower flux is also possible, but the economic gain is only realized when operating a one pass system.
Dual purpose multistage flash desalination plant provides fresh water with low cost at high desalting capacity, but requires high installment cost. Two stage reverse osmosis desalination plant requires only half of the multistage flash installment cost while producing water with comparable price. By combining sea water reverse osmosis plant with the dual purpose multistage flash plant, the capital and operating cost can be reduced and the excess power can be efficiently utilized.
The design parameters for such a hybrid plant will be the applied pressure and the recovery of the reverse osmosis plant and the number of stages and heat transfer areas for the multistage flash plant. The objective is to minimize the cost of water satisfying maximum total dissolved salt.
Different cost scenarios are suggested and their effects on the optimum parameters are investigated. It is concluded from this study that the savings obtained from scaling-up is more than that obtained from hydridization.
Existing fouling indices to measure the particulate fouling potential of reverse osmosis (RO) feedwater, the SDI and MFI0.45 do not include smaller colloidal particles. Therefore, the MFI using ultrafiltration (UF) membranes was developed (1000–100,000 Da pore size) to incorporate and measure smaller particles. A 13,000 Da membrane was selected as the most promising reference membrane for application in the MFI-UF test. This research investigates its application to (1) measure the particulate fouling potential of RO feedwater and (2) evaluate the efficiency of pretreatment processes on particle removal at two RO pilot plants. Where possible a comparison was made with the SDI, MFI0.45, and particle counts. Both RO plants use conventional pretreated surface water. Subsequently, the Rhine River plant uses ozonation, biological activated carbon filtration, and slow sand filtration while the Ijssel Lake plant uses ultrafiltration (150–200,000 Da). The MFI-UF of the influent feedwater was about 400–1400 higher than the corresponding MFI0.45 and SDI, due to the retention of smaller particles. A reduction in the particulate fouling potential, > -80%, was found by MFI-UF with pretreatment at both plants. For the larger particles the MFI0.45 gave a 90–≈100% reduction at the Rhine River plant, while the SDI gave more variable results: 70 > 90%.
The objective of this study was to develop a new measurement technique for the determination of pore size distributions (PSDs) of polymeric and ceramic membranes, including NF, UF, and MF membranes. The proposed method uses the fractional rejection (FR) concept of a solute in membrane pores. Experimental measurements were conducted using a high performance liquid chromatography (HPLC) equipped with size exclusion chromatography (SEC) columns and a refractive index (RI) detector. A specially designed membrane filtration unit was also used. Two different macromolecules, including nonionic polyethylene glycols (PEG) and natural organic matter (NOM) with ionizable functional (carboxylic and phenolic) groups, were used as solutes. Membrane PSDs, determined with PEG and NOM, can be defined as absolute and effective membrane PSDs, respectively. Two different types of membranes (flat-sheet polymeric and tubular ceramic) were used in this work. Experimental procedures include three major steps: (1) measurements of relative molecular mass (RMM) distributions of solutes included in the membrane feed and corresponding permeate, (2) the calculation of solute FR, and (3) PSD determination. The main results and advantages of this method are: (1) the PSD of various membranes with different pore sizes can be measured using a relatively easy method without significant limitations of pore size and membrane type; (2) various factors that affect membrane PSD, including pH, ionic strength, ion binding, and hydrodynamics, can also be evaluated; (3) the effective PSD of membranes with negatively-charged surfaces, and which exhibit significant shifts in PSD towards the lower RMM region can also be determined. © 2002 Elsevier Science B.V. All rights reserved.
Das Aus für's Salz: Übliche Polyamidmembranen zur Entsalzung werden leicht durch Chlor angegriffen, doch sulfonierte Copolymere, die durch eine direkte Copolymerisation mit einem disulfonierten Monomer entstehen, bieten sich als chlorbeständige Alternative an. Mithilfe solcher Membranen (siehe Bild) gelingt die leistungsstarke Entsalzung bei hohem Durchfluss.
The general rules established in abundant studies on removal of conventional pollutants from waters
by reverse osmosis and nanofiltration were reconsidered in this contribution in order to determine their
applicability for the removal of emerging contaminants. The new results on removal of organic pollutants
at trace concentrations from waters and wastewaters are presented, together with the assessment of the extent
to which the general findings and rules of NF/RO are valid and confirmed in the recent studies. Some specific
findings and conclusions from studies on the removal of emerging micropollutants are also highlighted.
The intensive development of agriculture and application of chemicals led to the contamination of many natural water reservoirs and groundwaters with nitrates. This paper reviews an attempt at removal of nitrate ions from tap water by means of the combined processes of reverse osmosis and nanofiltration. In the first stage, the water was filtered on nanofiltration membranes which resulted in the absence of bivalent ions in the obtained permeate. Then the filtrate was concentrated using reverse osmosis. Because the substances forming membrane scale (CaSO4, CaCO3) were removed from the filtrate, the efficiency of this process was limited mainly by the osmotic pressure of the retentate.
Reverse osmosis (RO) membranes provide a cost-effective water purification solution for wastewater reclamation facilities. RO membranes reduce total dissolved solids, heavy metals, organic pollutants, viruses, bacteria, and other dissolved contaminants in the water treatment facilities. Tertiary effluent, which includes fouling, colloidal, biological, scaling and organic fouling from a water treatment process is supplied to a RO system. Colloidal material is effectively controlled by the use of ultrafiltration and microfiltration membrane pretreatment. Chlorine can be added before the membrane pretreatment to control biofouling. The Bedok Demonstration plant in Singapore is one such commercial plant that has successfully used membrane based reclamation. RO technology is very important for communities who need to extend their water supply intake and for industries that require ultrahigh quality water.
Accurate characterization of membrane surface charge is vital for understanding membrane surface chemistry, separation performance, and fouling resistance. Streaming potential is the standard electrokinetic phenomena used to characterize a membrane's isoelectric point and zeta potential, which is related to the dynamic charge functionality at the membranesolution interface as function of solution pH and ionic composition. We have recently developed a new method for directly measuring membrane surface charge via direct surface titration. Direct surface titration enables identification of maximum surface charge density, fractional ionization as a function of pH, and the apparent pKa of a charged surface. We have employed this new characterization technique to assess the charge of several commercial polyamide reverse osmosis membranes and compare these results to charge determined from classical electrokinetic measurements.
Toray Industries and Toray Engineering have developed a new type reverse osmosis (RO) membranes and its process for seawater desalination, which brings advantages of high water recovery, low energy cost and lower plant installation cost. The new type RO membranes, "Brine Conversion Reverse Osmosis Membrane (SU– 820BCM)", shows a superb performance at a high pressure of more than 9.0 MPa and a high salt concentration more than 5.8% concentrated seawater. The newly developed "Brine Conversion Seawater Reverse Osmosis Desalination System (BCS system)" takes the fresh water from the concentrated brine water (salt concentration 5.8%, produced under 6.5 MPa) of first stage RO modules. The newly developed "Brine Conversion Seawater Reverse Osmosis Desalination System" (BCS system) can obtain 60% recovery of fresh water, taking from the concentrated brine water (salt concentration 5.8%, produced under 6.5 MPa) of first stage RO modules in addition to a conventional system desalination (40% recovery). The cost of producing fresh water can be saved approximately 15–20%. The space of plant is also reduced approximately 30% due to reducing the space of the pretreatment process. The continuous operating performance with SU–820BCM has proved to be in good conditions in the BCS pilot plant in Japan for more than 2 years. The total capacity of this plant is 210 m 3 /d with 60% recovery, and the quality of the produced fresh water has been maintained at the level of less than 200 ppm TDS, which satisfies their designed specifications for drinking water.
Model-predictive control algorithms are applied to a high capacity reverse osmosis (RO) membrane desalination process simulation that utilizes feed flow-reversal in order to prevent and/or reverse scale crystal formation on the membrane surface. A dynamic non-linear model which incorporates feed concentration and membrane properties is used for simulation and demonstration of optimally controlled feed flow reversal. Before flow reversal can take place on a high capacity RO plant, the flow into the membrane unit must be carefully reduced to eliminate the risk of membrane module damage and unnecessary energy consumption. A cost-function is formulated for the transition between the normal high flow steady-state operating point to a low flow steady-state operating point where it is safe to reverse the flow direction. Open-loop and closed-loop simulations demonstrate non-linear model-predictive control strategies that induce transition from the high-flow to low-flow steady-states in an optimal way.
Biostability of finished waters was assessed statistically using assimilable organic carbon, biodegradable dissolved organic carbon and heterotrophic plate counts. Biofilm growth on lined cast iron and polyvinylchloride pipe material was galvanized steel unlined cast iron,, assessed visually and statistically using potential exoproteolytic activity, which is a measure of biofilm cell density. Seven different treatment processes were used to simulate full scale treatment and distribution of ground, surface and saline sources to pilot distribution systems lined cast iron and polyvinylchloride pipes taken from galvanized made from unlined cast iron,, actual distribution systems. Bulk water biostability parameters as measured by assimilable organic carbon, biodegradable dissolved organic carbon and heterotrophic plate counts were lower in reverse osmosis finished water and higher in conventionally treated groundwater. Average finished water assimilable organic carbon indicated reverse osmosis and nanofiltration membrane processes reduced assimilable organic carbon relative to finished groundwater produced by conventional treatment or softening, and finished surface water produced by enhanced coagulation. This relationship was not observed clearly for biodegradable dissolved organic carbon or heterotrophic plate counts. Biofilm growth on coupons cut from the pipes used to build the pilot distribution systems typically decreased as the level of treatment increased with the exception of reverse osmosis finished water, which produced very high biofilm growth. However, the assessment of biostability indicated biostability generally increased as the level of treatment increased, and the general order of biostability of process finished waters was: membrane > precipitative > conventional; and the order of biofilm growth with respect to pipe material was unlined cast iron > galvanized > lined cast iron > polyvinylchloride. Hence, improved distribution system biological water quality, as measured by lower assimilable organic carbon, biodegradable dissolved organic carbon, heterotrophic plate counts and biofilm growth, was directly dependent on nonpurgeable organic carbon and improved as finished water nonpurgeable organic carbon decreased.
The Stefan-Maxwell multicomponent diffusion equations were used to characterize albumin transport in ultrafiltration membranes in both an unstirred batch filtration device and a well-stirred diffusion cell. We developed a theoretical model for ultrafiltrate flux and concentration in the filtration device that explicitly incorporates the effects of protein polarization, protein osmotic pressure, and a flux-dependent sieving coefficient. Experimental data were in good agreement with model predictions, providing quantitative evidence for the predicted dependence of the apparent sieving coefficient on flux. Experimental data in the diffusion cell indicate that the effective albumin diffusivity in the 50,000 molecular weight cut-off membranes was four orders of magnitude less than the Brownian motion value. The Stefan-Maxwell diffusivities evaluated independently in the two experimental systems were in excellent agreement, indicating the general applicability of the Stefan-Maxwell approach to protein transport in ultrafiltration membranes.
Model-predictive control algorithms are applied to a high capacity reverse osmosis (RO) membrane desalination process simulation that utilizes feed flow reversal in order to prevent and/or reverse scale crystal formation on the membrane surface. A dynamic non-linear model which incorporates feed concentration and membrane properties is used for simulation and demonstration of optimally controlled feed flow reversal. Before flow reversal can take place on a high capacity RO plant, the flow into the membrane unit must be carefully reduced to eliminate the risk of membrane module damage and unnecessary energy consumption. A cost function is formulated for the transition between the normal high flow steady-state operating point to a low flow steady-state operating point where it is safe to reverse the flow direction. Open-loop and closed-loop simulations demonstrate non-linear model-predictive control strategies that induce transition from the high-flow to low-flow steady-states in an optimal way while subjected to plant-model mismatch on the feed concentration, actuator magnitude and rate constraints, and sampled measurements.
Desalination of seawater and brackish water by reverse osmosis (RO) has become increasingly important for drinking water supply in a greater part of the world. The presence of high silica concentrations in some brackish water, however, limits the application of RO desalination due to the potential formation of silica scales that irreversibly deteriorate the membrane material and performance. This study investigates the feasibility of electrocoagulation as a pretreatment process to remove silica from the source brackish water. The effects of several electrical parameters, including electrode arrangement, current intensity and hydraulic retention time, were studied on the basis of silica removal efficiency. Bipolar configuration attained greater extent of silica removal as compared to monopolar configuration. Increases in charge loading generally improved the silica removal efficiency, but excessive hydraulic retention time (60min) was detrimental to the system performance. In this study, with no modification of the source water, silica removal efficiency up to 80% was achieved under a current intensity of 0.5A and a hydraulic retention time of 30min.The subsequent nanofiltration studies demonstrated severe flux declines over the first 3h, yielding only 70% of its initial flux for brackish water containing 100mg/L silica, and progressively lower with higher silica concentrations. For the pretreated water by electrocogulation, the extent of flux decline was markedly improved, suggesting that the pretreatment was effective for the attenuation of the flux decline. Electron micrograph images of the membrane autopsy also confirmed the lack of scale formation for the pretreated water as compared to those without pretreatment.
A pilot study on total organic carbon (TOC) removal in reclamation of municipal wastewater by RO has been conducted in Singapore. Secondary effluent from final clarifier was used as a feed to the system. RE4040-FL and RE4040-FE RO membranes from Saehan were applied in the study. The pilot results showed that on-line TOC measurements of the RO permeate were in range of 36–66ppb for RE4040-FL membrane at operating pressure of 60psi. For RE4040-FE membrane, they were in the range of 32–44 and 30–36ppb at operating pressure of 70 and 107psi, respectively. The low TOC level of the reclaimed water does not appear to be reported previously for the application of RO in reclamation of municipal wastewater. TOC and salt rejections of the RE4040-FE membrane were over 99.5 and 97.8%, respectively. The permeate quality and salt rejections of RE4040-FE membrane were better than that of RE4040-FL, which was comparable to High Grade Water (NEWater) quality.
Fouling induced by inorganic scaling is a major challenge limiting the use of reverse osmosis (RO) technology in many water treatment applications. This fouling can be reduced by using torsional vibration of flat sheet membranes to induce high shear rates at the membrane surface. We investigated fouling of RO membranes using a vibratory shear enhanced filtration process (VSEP®, New Logic Research, Emeryville, CA) system to treat a simulated brackish water source and a brine. Vibration substantially reduced membrane fouling and increased practical water recovery from 80% to over 90% for the brackish solution and from 50% to 75% for the brine. When the membrane was vibrated, fouling accounted for a much smaller fraction of the total hydraulic resistance during treatment of both the brackish solution and the brine. Vibration also increased rejection of major ions from between 70% and 88% to >95% in the brackish solution and >90% in the brine. SEM images indicated that vibration changed the morphology of the surface scale from a uniform layer of needle-like solids to a smoother layer that was apparently more hydraulically conductive. This morphological change seemed to increase the overall volumetric flux by opening up areas on the membrane surface that were otherwise covered by scales.
Wastewater reclamation and reuse are being widely implemented due to the lack of fresh water. When salinity is a limiting parameter to obtain the required water quality for agricultural uses, a desalination step is necessary to achieve it. Therefore, techniques such as nanofiltration (NF) or reverse osmosis (RO) can play an important role and have to be deeply studied in order to implement an economically feasible tertiary treatment. In this work, NF of a secondary effluent from a municipal wastewater treatment plant has been evaluated for increasing feed concentration in order to reach a final conversion of approximately 75%. Experiments were carried out with a laboratory plant containing a spiral wound membrane (DURASLICK-2540, General Electric) with an active area of 2.2m2. Tests were performed increasing volume concentration factors (VCFs) up to almost 4 and replicated three times to confirm the results statistically. After NF experiments an RO step of the retentate was carried out in order to concentrate the final brine. In NF experiments, for the highest VCF values, fluxes recommended for the membrane maker (17 Lm−2 h−1) were produced at a transmembrane pressure (TMP) of 3.2 bar. The TMP hardly increased with the VCF. NF membranes yielded a conductivity retention index around 42%, reaching nearly 99% for sulphate ions and only 23% for chloride ions.
This study identified the membrane fouling of a two-stage RO process of the Bai-sha brackish water desalination plant facing serious fouling problems. Two membrane modules, one from each stage, were autopsied and diagnosed for the cause for the failure of the RO system. Different morphologies were exhibited on the fouled membrane. Results suggested that the fouling on the first-stage membrane tended to be organic and biological, while that on the second-stage membrane appeared to be scaling. Higher than 85% of the foulants on the first stage membrane were organic substances in opposed to the 5 to 8% of those on the second stage membrane. However, the total organic matter on the second stage membrane was more than that on the first stage one. The thick layer of scalants on the surface of the second-stage membrane was identified to be calcium carbonate of which the crystal was clearly seen in the SEM images. The scaling was thickest at the outlet of the membrane. Huge amount of microbes were found on both membranes. The FTIR results also suggested the existence of extracellular polymeric substance (EPS) on the first stage membrane. This study recommended that the recovery rate, pH and the potential for bio-fouling should be defined at the real operation.
An earlier Kuwait Institute for Scientific Research (KISR) study on subsurface water rise problems in residential areas of Kuwait recommended drainage by deep wells to lower levels and maintain the subsurface water at a desired level. A large quantity of water needs to be permanently pumped for this purpose. The quality of the pumped water is likely to prohibit its direct use. Disposing of the water as waste is a loss that Kuwait cannot afford in view of its meager, over-stressed and practically nonrenewable natural groundwater resources. Therefore, experiments were conducted by KISR at the Kifan site to desalinate the rising subsurface water using reverse osmosis (RO) brine staging. Operation of these experiments lasted for about 5 months. The aim of these experiments was to test the technical feasibility of increasing the productivity of the tested RO systems using brine staging. This paper highlights the brine-staging concept and presents the data collected and an evaluation of the data. The data collected indicate that the average recovery obtained was 48%, availability of the brine staging RO unit was 97% and the increase in recovery using brine staging resulted in a significant reduction in the specific power consumption by about 37%.
Currently, most large scale seawater desalting complexes are dual-purpose Multi-Stage Flash (MSF) plants producing both power and desalinated water. These plants produce high purity distilled water and also provide excess electrical power for sale at a typical ratio of 10 MWe power per 1 million gallon per day (MGD) of water.In the hybrid MSF/RO desalination power process, a seawater Reverse Osmosis (RO) plant is combined with either a new or existing dual purpose MSF/power plant with the following advantages: 1. The capital cost of the combined RO-MSF plant can be reduced.2. A common, considerably smaller seawater intake can be used, in view of the smaller feedwater requirements for RO plants.3. Product waters from the RO and MSF plants are blended to obtain suitable product water quality. Taking advantage of the fact that the MSF product typically exceeds potable water specifications, the product water specification in the RO system can thereby be reduced.4. A single stage RO process can be used and the RO membrane life can be extended because of the reduced product water specification.5. Electric power production from the MSF plant can be efficiently utilized in the RO plant, thereby reducing net export power production.6. By blending with RO product water, the temperature of the MSF product water is reduced.
The nanofiltration (NF) membranes and their properties are quite diverse, but can generally be described as having rejection characteristics that range from “loose” RO to “tight” ultrafiltration. The uniqueness of these membranes is highlighted by their ability to selectively reject different dissolved salts, and have high rejection of low molecular weight, dissolved components. Nanofiltration membranes are mainly used to partially soften potable water, allowing some minerals to pass into the product water and thus increase the stability of the water and prevent if from being aggressive to distribution piping material. Additionally, NF membranes are finding increasing use for purifying industrial effluents, and minimizing waste discharge. The key to using NF membranes for particular application is the selection of a membrane with appropriate rejection characteristic and the design of a suitable process. NF membranes are generally characterized by a high charge density and pore sizes in the range of nanometers. The surface charge is most often negative and has the greatest effect on the selective passage nature of these membranes. The design of a NF system can often be more complex than a RO system. Because the required transmembrane pressure is so low, a system design that will result in balanced flux throughout the array is difficult to achieve. One common approach is to design NF systems with multiple element types. Such so called “hybrid” designs can help more finely control flow in the NF system. Also, membrane fouling can cause a change of rejection selectivity and/or reduction of membrane permeability that could affect both the water quality and operating cost due to increased energy requirement and higher consumption of chemicals needed for stabilization of permeate. The rejection characteristics of NF membranes depend on chemistry and surface charges of the separating barrier layer, ionic composition and concentration of feedwater and operating parameters of the NF system: recovery rate and permeate flux. Although, theoretical models have been developed to calculate selective ion rejection of NF membranes, they are mostly adequate only for simple water systems in limited range of water compositions and concentrations. In algorithms applied for projection of permeate composition in commercial NF systems, the theoretical models are augmented by empirical correction coefficients developed from field results. Selection of proper NF membrane type and prediction of performance is further complicated by membrane fouling. In NF projects involving treatment of feedwater with high concentration of dissolved organics the membrane selection process usually include pilot unit operation to evaluate stability of salt rejection and water permeability of candidate membrane elements. The paper will discuss present offering of commercial NF membranes, case studies and models applied to calculate their performance. This will also include information on recently developed NF membranes with low fouling characteristic that are successfully applied in the world largest (150,000 m3/d, 40 mgd) NF plant in Boca Raton, FL. The process of extensive field testing and parallel membrane performance optimization that led to selection of these nanofiltration elements for the Boca Raton plant will be described as well.
The need for appropriate pre-treatment to ensure optimum performance of reverse osmosis (RO) systems is well understood. RO manufacturers recommend that the SDI should be lower than 3. An increase of SDI involves rapid fouling of the RO membranes, which then increases the maintenance time duration. Conventional pre-treatment is not 100% secure to achieve this recommendation. Membrane filtration and especially ultrafiltration (UF), starts to be recognised as the best pre-treatment before RO. References of the membranes manufacturers are growing up but the knowledge of the real benefits of membrane processes compared to conventional ones in terms of both capital investment cost and operating cost reduction is still missing. In this paper, studies on a pilot unit coupling two different pre-treatments and a standard RO membrane element have been carried out on a real influent of the Mediterranean Sea at Palavas les Flots (France). SDI of the raw seawater was comprised between 6.1 and 6.4. Two pre-treatments have been compared, a conventional sand filter and a UF membrane with a proprietary unique design from Polymem [1,2]. The filtration modules are constituted with polysulfone hollow fibers working in a dead-end outside–in filtration mode with periodic backwashing. Molecular weight cut off was 100 kDa. Long-term experiments have shown that the SDI after the UF modules was 1.2–2 while it was 5.8–5.9 with the sand filter. Decreasing of 28% of the RO permeability was measured in 30 days with sand filter pre-treatment. Frequency of RO chemical cleaning was then estimated between 12 and 18 days. On the same seawater, with UF pre-treatment RO permeability decreasing was 0% during 20 days operating which would involve no chemical cleaning demand. Capital investment cost and operating cost benefits of UF have been estimated. It appears that these costs are comparable to those encountered in drinking water production by membranes.
In this paper, the performance of the full-scale RO process with highly permeable membranes and the governing mechanisms were carefully studied. It was found that the performance of a full-scale RO process could be controlled by two possible mechanisms, namely mass transfer rate and thermodynamic limitations. Under relatively low driving pressure, it was controlled by mass transfer rate (water flux) of the membrane. However, with the highly permeable membrane, it is possible that the performance is limited by the thermodynamic limitation, in which the osmotic pressure becomes equal to the driving pressure inside of the membrane channel. A process controlled by thermodynamic limitation is an extremely case of the hydraulic imbalance problem. When it occurs, it means part of the membranes in the processes do not contribute to permeate production. More complicated are situations in the intermediate pressure range, in which both mechanisms contribute to, but none of them can dominate, the performance of the process.
Some innovative concepts and theories on the performance of the full-scale RO processes were developed. These concepts and theories may provide better qualitative explanations for the behaviors often observed in the full-scale RO processes. A better quantitative simulations or predictions of the performance of the process were developed upon these concepts and theories. Experiments were carried out on a pilot membrane process of 6 m membrane channel to imitate the performance of the full-scale RO under various conditions. The experimental performance data were compared with theoretical simulations and excellent agreement was obtained.
Another focus of this current study was on characterization and modeling of membrane fouling in the full-scale RO process. Colloidal fouling experiments were conducted to study the fouling potential of feed water and a new fouling indicator was proposed. The indicator can be directly used in the mathematical model to simulate fouling development in the full-scale RO processes. Model simulations showed that under certain condition (thermodynamic restriction), the recovery or average permeate flux of a full-scale RO process would maintain a constant value even membrane fouling was taking place. Experimental verification of the simulation results is currently under way. With the new developments and findings in this area, methods or protocols for optimization of full-scale processes of the highly permeable RO membranes were suggested.
Reverse osmosis (RO) technology has been used for the reduction of the salt content of water since the late 1960s. The RO membrane elements are available for a variety of desalination applications, treating water from sources ranging from seawater and brackish water to waste water for use in applications ranging from industrial and process water to drinking water. In recent years major advancements have been made in the flux and salt rejection capabilities of the membranes. It became apparent that a high flow seawater membrane element was needed particularly for cooler, lower salinity water and during the mid 1990s a product was developed to meet these needs. In 1999 high flow seawater elements, Koch Membrane Systems product Fluid Systems™ TFC® 2822HF-370 elements were installed in a new plant producing 5230 m3/d process and boiler feed water for EDIPOWER at Archi Marina San Filippo del Mela – Sicily, Italy. This paper is a case history describing the plant and looking at the performance of the membrane using Koch Membrane Systems NormPro® to normalise the data.
Desalination by using reverse osmosis (RO) membranes has become very popular for producing freshwater from brackish water and seawater. Membrane lifetime and permeate flux, however, are primarily affected by the phenomena of concentration polarization and fouling at the membrane surface. The scope of the current paper was to critically review the literature on the fouling phenomena in RO and ultrafiltration (UF) membrane systems, the analytical techniques used to quantify fouling, preventive methods, and membrane cleaning strategies. The paper also makes specific recommendations on how scientists, engineers, and technical staff can assist in improving the performance of these systems through fundamental and applied research.
The absorption of water in commercially available reverse osmosis membrane active layers (FT30 by Filmtec and LF10 by Nitto Denko) is investigated by a combination of measurements of water mass uptake and biaxial stress as a function of relative humidity. The experiments are enabled by bonding the active layers of the membranes to either a quartz crystal microbalance or a glass cover-slip using polyimide as an adhesion layer and subsequently removing the porous polysulfone support layer with an organic solvent. Membranes from these two suppliers behave similarly. Water mass uptakes of the active layers are approximately 12% of the mass of the active layer when the relative humidity is changed from 0% to 95%. This degree of water absorption produces a compressive biaxial stress of ≈ −20MPa. The changes in water mass uptake with relative humidity resemble a Langmuir adsorption isotherm when the humidity is low and the Flory–Huggins theory when the humidity is high. By combining the measurements of water mass uptake and biaxial stress, we estimate that the specific volume of water in the active layers is ≈ 0.28cm3g−1. The self-diffusion coefficient of water in the polyamide active layers of FT30 (DS=0.8×10−9m2s−1) and LF10 (DS=1.2×10−9m2s−1) were calculated from the water mass uptake measurements, water permeability values reported in the literature and assuming the solution–diffusion mechanism for water transport. These values for DS are a factor of 2–3 smaller than the self-diffusion coefficient of liquid water (DS=2×10−9m2s−1) and comparable to theoretical estimates of DS in the active layer of FT30 membrane using the free-volume model.
Porous filtration membranes such as microfiltration and ultrafiltration membranes have been widely applied in various industries. Recently nanofiltration membranes have been commercialized.Characterization of the membrane pore structure, such as pore radius, pore density, pore shape, pore length, tortuosity, and so on, becomes more and more important and characterization methods must be established. Various methods to characterize the pore structure of porous membranes will be reviewed. Firstly, the microscopy observation method which is the most direct method to characterize the membrane pore structure is reviewed. Atomic force microscopy recently developed has been applied for the membrane observation. Secondly, methods based on bubble pressure and gas transport will be reviewed. This method can measure the pore size distribution of a membrane under wet conditions. The third method is thermoporometry. The temperature of liquid solidification and/or solid melting is lower in smaller pores and thus by measuring the freezing and/or melting thermodiagram, the pore size and its distribution can be determined in wet environments.These three methods are not directly related with the solute or particle permeation performance which is the most important characteristics of separation membranes. Therefore the final method reviewed will be the characterization based on molecular transport through a membrane. Various transport models have been developed and they can be used for the characterization. The models and structural analysis by using the models will be explained.
Experimental data on properties and applications of charged reverse osmosis (RO) membranes have been reviewed. Experimental findings concerning membrane rejection as a function of concentration and the valency type of feed electrolyte solutions, ion-exchange capacity of membrane matrix, pH value of feed solutions and transmembrane volume flux have been shown to be in qualitative agreement with a simple theory based on Donnan's ideas, though remarkable quantitative deviations have also been observed. A number of new explanations to those deviations has been suggested. Areas of the optimum charged RO membrane applications have been shown to be the treatment of dilute electrolyte solutions at low working pressures (nanofiltration), namely: conditioning brackish waters, water softening, removing small amounts of toxic ions and recovery of valuable metals from industrial waste waters, purification of water from dissociating organics. Recently, the separation of amino acids and proteins according to their pK values has also been becoming an ever more promising application.
Several parameters are known to influence the passage of salts through a reverse osmosis membrane. These parameters include characteristics of both the membrane and the feed water. Of these parameters, the least understood is the effect feed water concentration has on salt passage. At high and very low feed salinities, salt passage can increase by a factor of two or more. As an increasing number of RO systems are designed to treat water at these salinity extremes, a better understanding of this salinity effect is necessary to accurately predict the permeate quality of these systems. This study seeks to demonstrate and characterize the salinity effect on different RO elements treating different feed waters. The magnitude of the salinity effect at any given feed salinity is shown to be influenced by membrane charge and feed water composition. The results of the study on individual elements are used to accurately predict the salt passage in an existing full scale RO system.
The quality of potable water is such that the concentration of nutrients available for growth of microorganisms within distribution systems is limited. In such systems carbon is often the growth limiting nutrient. Research conducted in the Netherlands has indicated that low levels (<10 μg/L) of available organic carbon in water is sufficient to maintain an actively growing population of heterotrophic, or organic carbon utilizing, bacteria in aquatic systems. However, the ability of commercially available and cost effective technologies to achieve such low concentrations of assimilable organic carbon in full-scale water systems is doubtful. Reverse osmosis (RO) systems have been used for many years to effectively remove contaminants from source waters. We challenged a water distribution system simulator (DSS) with water from a municipal system and water that was treated using an RO system under two concentrations of residual free chlorine to evaluate the effect of this disinfectant on biofilms in contact with low nutrient water. Our results showed that biofilm densities in the DSS carrying low nutrient RO treated water were lower than biofilm densities taken from the DSS when it carried water directly obtained from a municipal system.Key words: water distribution systems, reverse osmosis, biofilms, heterotrophic plate count, HPC, chlorine, assimilable organic carbon.
Nonvolatile dissolved organic carbon (DOC) in reclaimed wastewaters and groundwater was characterized and indicators of wastewater origin were identified. Over 50% of the DOC in activated carbon and reverse osmosis effluents was classified as hydrophilic, and no humic acid was isolated. In groundwater partially recharged by the reclaimed wastewaters, only 16% of the DOC was hydrophilic, 50% of the DOC was fulvic acid, and humic acid was recovered. The H:C ratios of the isolated fulvic acids were higher in the wastewaters and recharged groundwater than in deep well water not affected by recharge. N:C ratios in the wastewater and recharged groundwater fulvic and humic acid fractions were also higher than in the deep well water. The 1H NMR spectra of the effluent and recharged groundwater fulvic acid fractions exhibited a characteristic fingerprint pattern, indicating a correlation between origin and spectral appearance. Gas chromatography-mass spectrometry analysis confirmed the presence of specific trace organic compounds, including EDTA and alkylphenol polyethoxylate residues, in the wastewaters and recharged groundwater.
The Dublin San Ramon Services District (DSRSD) has constructed a 2.5 mgd tertiary treatment facility composed of microfiltration, reverse osmosis, and ultraviolet disinfection. The facility has been approved by the California Department of Health Services and the California Regional Water Quality Control Board for production of water for groundwater injection into a potable water aquifer. In an effort to mitigate public concerns regarding the injection of recycled water, DSRSD has carried out intensive and comprehensive water quality tests, including a wide variety of organic and inorganic compounds, endocrine disrupting compounds, disinfection by-products, seeding for virus challenge studies, toxicity tests, and testing for radioactive components. The results of the testing program are compared with the quality of local potable water and ground water to allow an evaluation of the effectiveness of the treatment processes in producing potable quality water.
Boron has been widely used in various manufacturing industries, and the level of boron in the industrial effluent can range from as high as several grams per liter to as low as a few micrograms per liter. Due to the potential adverse health effect of boron on human beings, the World Health Organization (WHO) has provided a guideline for the boron concentration in drinking water to be less than 0.5 mg/L. Therefore, the boron-containing effluents or solutions should be treated before they could be discharged into natural water bodies. This paper critically reviews various technologies used for boron removal, including those recently developed, electrocoagulation (EC) and double-layered hydroxide (DLH) compounds, as well as conventional and advanced treatment technologies such as chemical precipitation, ion exchange, reverse osmosis, adsorption, liquid−liquid extraction, and electrodialysis. Particular focus is given to the comparative performance and advantages and disadvantages of these technologies for boron removal. EC and DLH have been proven to be highly effective for boron removal from solutions with a high boron concentration, while a DLH compound alone can effectively treat solutions with low boron concentrations (<50 mg/L) to the WHO recommended drinking water standard (≤0.5 mg/L). Pilot- and full-scale trials, however, need to be carried out in order to implement EC and DLH compounds for removing boron in a full scale.
Precipitation of sparingly soluble salts is one of the main factors limiting the recovery in reverse osmosis (RO) of brackish water sources. Recoveries can be increased and antiscalant usage eliminated or reduced by applying flow reversal to RO process trains. Flow reversal works by changing the place of the entrance and exit of the pressurized feed before the induction time of the supersaturated solution along the membrane wall runs out and precipitation occurs. Reversing the flow before the induction time of the system is reached replaces the supersaturated brine at the exit with the unsaturated feed flow and thus “zeroes the elapsed nucleation time”, thereby resetting the induction clock. Laboratory experiments successfully demonstrated the technical feasibility of this concept by periodically exposing RO membranes to undersaturated solution after exposure to supersaturated calcium sulfate solution (bulk saturation index up to 3.0) formed from calcium chloride and sodium sulfate. The induction time to precipitation fouling without periodical switching of solutions was 150−270 min for stirred solutions. Periodic switching of solutions prevented precipitation for >480 min from stirred solutions. In follow-up experiments, a small scale pilot unit containing 2.5 in. diameter spiral RO elements was run continuously for 22 h with a calcium sulfate supersaturation index of 5.4 on the wall of the last element, when operated under reverse flow conditions. Without reverse flow the last RO element began to scale within 1 h.
In pressure‐driven membrane processes (reverse osmosis, nanofiltration, ultrafiltration, and microfiltration) a pressure exerted on the solution at one side of the membrane serves as a driving force to separate it into a permeate and a retentate. The permeate is usually pure water, whereas the retentate is a concentrated solution that must be disposed of or treated by other methods. Membranes may be polymeric, organo‐mineral, ceramic, or metallic, and filtration techniques differ in pore size, from dense (no pores) to porous membranes. Depending on the type of technique, salts, small organic molecules, macromolecules, or particles can be retained, and the applied pressure will differ. This paper reviews the principles behind the different techniques, the types of membranes used, rejection mechanisms, and process modeling. Applications of pressure‐driven membrane processes are also considered, including reverse osmosis and nanofiltration for the treatment of wastewater from landfills and composting plants, nanofiltration in the textile industry, and ultrafiltration and microfiltration in drinking water production and wastewater treatment.
Lastly, the paper discusses recent developments, including techniques to prevent membrane fouling by modifications affecting surface roughness or hydrophilicity/hydrophobicity, or by cleaning the membranes, and methods for treating or disposing of the retentate.
Cationic polymers used in traditional water and wastewater treatment, in theory, will bind to the partially negatively charged polyamide membrane during reverse osmosis (RO) treatment. This study tested a variety of cationic, anionic, and nonionic polymers in terms of (1) aiding in turbidity removal when used in conjunction with alum coagulation [10 mg/L as Al2(SO4)3·14H2O], sedimentation, and dual-media filtration; and (2) their binding affinity toward a polyamide membrane. Binding affinity was tested by exposing polyamide RO membranes to 50 mg/L of each polymer for 48 h and then conducting attenuated total reflectance Fourier transform infrared (FTIR) spectroscopy on the membrane samples and principal-component analysis (PCA) of the FTIR spectra. Results from the turbidity removal tests showed that cationic polymers provided the lowest median effluent turbidity (0.03–0.11 NTU), followed by anionic polymers (0.06–0.08 NTU), and finally nonionic polymers (0.11–0.17 NTU). Although PCA of the FTIR spectra did detect differences in polymer-exposed membranes vs. a control, no discernable difference in RO membrane performance was observed. Therefore, under the conditions studied, the issue of “membrane poisoning ” caused by organic polymer absorption onto polyamide membranes was minimal. © 2005 American Institute of Chemical Engineers Environ Prog, 2005
Crude oil desalter effluent from a Tehran oil refinery was treated by a hybrid UF/RO membrane separation process. Ultrafiltration (UF) was used primarily to remove the emulsified oil droplets followed by the removal of total dissolved solids (TDS) via reverse osmosis (RO). The UF membrane was a hydrophilic flat sheet polysulfone ultrafiltration membrane with MWCO of 100 kDa while the RO membrane was a spiral-wound thin-film composite polyamide. Effect of operating conditions such as transmembrane pressure and crossflow velocity were studied in UF pretreatment. The experimental results showed that the UF membrane removed more than 75% of the oil and can be considered as an effective pretreatment. Moreover, RO removed more than 95% of TDS from the desalter effluent. It was concluded that treatment of the desalter effluent using the UF/RO membrane separation process was feasible and desirable.
It is shown that the combination of two once-through MSF plants, or once-through MSF and RO with power recovery, can lead to more economical plant designs than the brine recycle process currently in vogue. Various combinations are compared wtih a base case in order to illustrate the considerable power savings and improvement in the overall cost economics which ensue.
In the last decade desalination has been considered as a solution for potable water needs only for specific water scarcity countries having cheap fuel. Now, desalination is extensively used, even where it was unthinkable twenty years back, due to reduction in desalination cost. The cost reduction is due to new developments and improvements in desalination technologies, particularly in RO technology. The RO is a well accepted technol-ogy due to recent increase in energy prices and takes up a major share in worldwide market. But, it is not able to achieve its proper share in the Arabian Gulf market due to difficult seawater composition and extensive historical use of thermal desalination. But RO still has potential in hybrid systems in the Arabian Gulf to account for seasonal and night to day fluctuations in the demand for power and water. There is a need for an accurate methodology for evaluation of desalination costs to help in selection of appropriate technology suitable for a specific location, for process design and other requirements. However, existing methodologies and soft-ware packages do not account for all the parameters that contribute for desalting cost and their accuracy is limited to specific conditions. This paper presents an overview of the trends in desalination costs for major desalination technologies like Multi Stage Flash, Multi Effect Distillation and Reverse Osmosis and review of costing methodologies.
Concentrate of nanofiltration and reverse osmosis installations is an increasing problem, especially for inland membrane installations. Introduction of membrane filtration in The Netherlands is severely hindered by the con-centrate problem. Two approaches are viable for solving or reducing the concentrate problem: (1) low recovery NF/RO without anti-scalant dosing, (2) Zero liquid discharge. This research focuses on the second option: Zero liquid discharge NF/RO. First and main problem to be solved with zero liquid discharge is to increase the recovery of the membrane installation to its limits, without increasing the costs of water produced. A high recovery (>99%) is necessary to reduce energy consumption and costs for evaporation of the remaining waste stream (<1%). The only possibility to achieve a very high recovery in NF/RO, is removing the scaling components from the feed water. A very important advantage of removing the scaling components is that the nanofiltration or RO can be operated at high fluxes. In this paper the results of two pilot experiments are reported. One treatment concept was developed for surface water treatment and one for groundwater treatment. The sur-face water treatment concept consisted of fluidized ion exchange to remove positive multivalent cations, and then followed by ultrafiltration, nanofiltration and granular activated carbon filtration. With this setup a recovery of 97% was achieved. To achieve an even higher recovery it is also important to remove silica from the feed water because silica can limit the recovery. Silica can be removed at high pH during co-precipitation with magnesium hydroxide. The groundwater concept consisted of: precipitation at high pH, then followed by sedimentation, weak acid cation exchange and nanofiltration. With this setup a recovery of 99% was achieved.
Pre-treatment of seawater feeding reverse osmosis (RO) membranes is a key step in designing desalination plants. The pre-treatment process must be adapted to the seawater quality to be treated (wells, open intake, etc.), especially when treating surface seawater with highly variable quality. After a general presentation of different pre-treatment options in relation to the seawater quality, this paper is focussing on two case studies, two open intake seawater pre-treatment upstream reverse osmosis desalination. The first site is located in the Gulf of Oman (Indian Ocean), the second in the Persian Gulf. The pre-treatment uses different technology strategies, conventional pre-treatment (coagulation and direct filtration on dual media filters) and innovative technologies (high rate dissolved air flotation, ultrafiltration and microfiltration) according to the water quality. The parameters taken into account for the water quality characterisation are the suspended solids, turbidity, fouling tendency, organic matters and algae content. This paper presents the pre-treated water quality achieved by the two types of pre-treatment and discusses potential impacts on RO hydraulic performances.
Gulf countries experienced rapid growth in the last four decades from oil production and its price increase. Natural water resources are very limited to meet this growth, and as result, desalted seawater in Kuwait became the main source of potable water, about 93% in 2002. The electric power and desalted water, produced in co-generation power desalting plants (CPDP), consumptions are continuously increasing, almost doubled every 10 years, due to population and standard of living increases. This led to the consumption of huge amounts of fuel, draining the country main fuel (and income) resource, and negatively affecting the environment. One tenth of Kuwait's oil production was consumed by the CPDP in 2003. If the trend of almost doubling the consumption every 10 years prevails, the total oil production may not be sufficient to desalt seawater for people to drink, and to produce power to run space air conditioning units (a necessity for Kuwaiti harsh weather). It is essential therefore to look for energy efficient ways to produce power and desalted water so as to save the nation's income of these non-renewable fuel resources, to save the environment and indeed life itself in Kuwait, and this is the objective of this paper. It reviews the presently used desalting methods and their energy demand, and the correctness of fuel allocation formulas for CPDP, to determine the most efficient methods to apply and the less efficient ones to avoid. Fourteen desalting cases are analyzed by using the current practice, with and without combination with power generation plants (using steam or gas or combined gas/steam turbines cycles). The specific fuel energy consumed and the emitted CO 2 , SO x , and NO x per m 3 desalted water were calculated for each case. The results show that operating thermally driven desalting systems by steam directly supplied from fuel-fired boilers is the most inefficient practice, and should be avoided. The use of the gas/steam turbine combined cycle, which is also the most efficient power-generation cycle, to drive seawater reverse osmosis (SWRO) desalination plants is the most efficient combination. Also, all conservation measures in utilization of both water and power should be applied. Reclamation of waste water, at least for non-potable water needs must be promoted, because it consumes less energy and at cost much lower than those of desalting seawater.
The Ministry of Water Resources successfully conducted an experimental study on the use of solar power to desalinate brackish ground water at their Heelat ar Rakah camp, a remote location some 900 km south of Muscat, the capital of Oman. The system comprises components for pre-treatment of pumped well water to separate hydrogen sulphide, acid dosing to correct the pH, cartridge filtration, a solar powered reverse osmosis unit, and a reject-water evaporation pond. The solar powered system comprises a 23.2 m2 solar photovoltaic generator with a peak capacity of 3250 Wp, a boost charge battery of 200 Ah at 48 VDC, a charge controller, a sine-wave inverter of 3000 VA with an output of 230 V, 50 Hz, and necessary controls and instrumentation. The design water output of 5 m3/day during 5 h (of each day) was achieved, with the output sometimes exceeding 7.5 m3/day. The average cost of production is estimated at US$6.52/m3 over the 20-year lifetime of the equipment. The study has demonstrated that solar-powered reverse osmosis systems are particularly appropriate to remote locations that have limited or no access to supply services such as fuel, power or potable water.
Reverse osmosis (RO) has become an important process for desalting water. It requires an efficient control system to maintain costs at acceptable level and therefore dynamic models are essential. Although it is possible to find in the literature steady-state models and some dynamic models obtained by parameter identification, there are no reports about lumped parameter dynamic models for control purposes obtained by application of physical laws. Such models are useful not only to design model-based control systems but also for the implementation of fault tolerant systems based on fault detection and isolation (FDI) methods, as well as to analyze transient characteristics of the plant. In this paper, models from the literature are shortly analyzed and a simple lumped parameter model for control purposes, which is derived from physical laws, is proposed. Moreover, a block-oriented library for MATLAB/SIMULINKtrade is presented, so that different plant configurations can be implemented as block diagram to simulate the system and to test control algorithms.
Feed-forward/feedback control techniques that utilize Lyapunov-based control laws are implemented on a high recovery reverse osmosis desalination plant model. A detailed mathematical model of a high recovery reverse osmosis plant is developed. This model incorporates the large spatial variations of concentration and flow-rate that occur in membrane units during high recovery operation. Bounded nonlinear feedback and feed-forward controllers are developed and applied to this system. The application of these controllers is demonstrated in the context of a high recovery reverse osmosis process simulation. The scenarios demonstrate the ability to compensate for the effects of large time varying disturbances in the feed concentration on specific process outputs with feedforward/feedback control.