Electrodialysis Research Articles

Comparative study on salinity removal methods: an evaluation-based stable isotopes signatures in ground and sea water

This research aims to attain the optimal method of removing the high salinity concentrations without its effect on the balance or accuracy of stable isotopes measurement of deuterium and oxygen-18 (δ18O, δ2H). Four treatment methods (i.e., distillation, vacuum distillation, electro dialysis and ion exchange) were applied for nine samples, which were obtained from different water sources (sea, groundwater, river).l Worth to notice that the samples have Electrical Conductivity (EC) ranged (1000–60,000 µs/cm). Liquid–Water Isotope Analyzer used to measure the isotope concentration of δ18O, δ2H. The research findings of the four applied methods revealed their effectiveness with various percentages (normal distillation: 92.37%; vacuum distillation: 88.31%; electro dialysis: 94.85%; ion exchange: 99.62%). In addition, the investigation was conducted a clear correspondence measurement of (δ18O, δ2H) isotopes before and after treatment. The four methods results indicated that samples with EC ranged (1000–5000 µs/cm) have no effect on stable isotope readings. Whereas, samples with EC higher than 10,000, have substantial influence on the stable isotope readings. Finally, vacuum distillation method attained the best results among the treatment methods for EC ranged (10,000–60,000 µs/cm) without affecting the isotopic content of (δ18O, δ2H). There is a clear correspondence of the stable isotopic measurements before and after treatment, for all the selected samples.

Effect of reverse osmosis pre-processing of acid whey and electrodialysis current density on process performance

Acid whey (AW) is the main side-stream from acidified dairy products, known for its high contents of lactic acid and minerals. The present work investigates the effect of reverse osmosis (RO) pre-processing of AW (ROAW) and the current density during electrodialysis (ED) on the ED process performance. Firstly, the limiting current density of the ED system when treating AW and ROAW was determined. Then, the AW and ROAW have been demineralized and deacidified at under-limiting or over-limiting current density batch operating conditions. RO pre-processing of AW and current density strongly affect the demineralization rate and solutes mass transport across the membranes. Lactate transport can be rationalized by the weak acid dissociation mechanism, while water splitting played a minor role in the ED process performance. Among cations, calcium and magnesium were most affected by RO pre-processing, due to their high affinity to the cation exchange membranes. Lactose and galactose were found in small amounts in the concentrate solution, while no glucose was detected for most conditions even though the glucose content decreased in the diluates. The energy consumption was up to 2 fold higher for ROAW compared to AW

Techno-economic analysis of a hybrid electrodialysis–batch reverse osmosis process for brackish water desalination

Abstract Hybridization of electrodialysis (ED) and batch reverse osmosis (BRO) process is used to reduce the brine volume and water production cost. The ED process has the benefit of high water volume recovery in brackish water desalination, while reverse osmosis can produce pure water at a low production cost. Here, a simple hybrid process layout is preferred in which the ED process is kept in the reject stream of the BRO process and permeate from both ED and BRO is mixed. Recovery of the ED process is kept at 70% which can decide the blending ratio of ED and BRO permeates. The capital cost and operating cost of ED and BRO processes are used to calculate water production cost. The water production cost from the hybrid ED–BRO process is found to be 0.22 $ m−3 of freshwater when the feed concentration is 1,100 ppm. The cost increases from 0.20 to 0.34 $ m−3 with feed concentration from 1,000 to 2,000 ppm. In the cost, a major portion comes from the capital equipment in which the highest contributor is the membrane for both ED and BRO processes.

Impact of the Donnan electrolytes on selectivity of cation exchange membranes evaluated via the ionic membrane conductivity

The selectivity of an ion exchange membrane (IEM) is an essential property in related electro-chemical separation and clean production processes. The impact of the Donnan electrolytes on the counter-ion selectivity of three representative cation exchange membranes (CEMs) evaluated via the ionic membrane conductivity is systematically studied in the mixed MgSO4/Na2SO4 and H2SO4/Na2SO4 electrolytes, over an external total sulfate concentration range of 0.1 ∼ 1.0 M. The counter-ions selectivity is decoupled into the partitioning selectivity coefficient (Kji) and the mobility ratio (uim/ujm), both of which are related to the CEM conductivity. If the Donnan electrolytes conductivity is excluded, for the heterogeneous CEM (3361BW), the selectivity calculated from the ion-exchanged conductivity (κE) can be perfectly matched with the electrodialysis (ED) results under a lower external sulfate concentration (0.1 M). The Mg2+/Na+ selectivity values of two homogeneous CEMs (Nafion117 and CSE) obtained from the nonlinear correlation method derived from the Kohlrausch's law (σ) are closer to the ED values, while the linear correlation approaches are more suitable at the presence of H2SO4. By analyzing the variation of Kji and uim/ujm with the κE separately, the main reason for the variation of the Mg2+/Na+ selectivity for these three CEMs, when the external electrolytes concentration increases, is the different equilibrium partitioning selectivity coefficients (KNa+Mg2+) between the membrane and the solution. On the contrary, the H+ ions transport much faster than the Na+ ions within the CEMs, and it is the change of this mobility ratio that causes the different H+/Na+ selectivity results. This work not only expands the application of the proposed conductivity method, but also provides a new perspective for studying the sorption and transport mechanism of ions in electro-chemical processes based on IEMs.

Fouling of ion-exchange membranes during electrodialytic acid whey processing analysed by 2D fluorescence and FTIR spectroscopy

Acid whey (AW), a by-product from the production of acidified dairy products, contains high amounts of lactic acid and minerals that can be recovered by electrodialysis (ED). To better understand the process and improve its efficiency, the objective of this study was to investigate fouling of ion-exchange membranes (IEMs) during ED of AW and concentrated AW by reverse osmosis (ROAW), underlimiting (ULCD), limiting (LCD) and overlimiting current density operating conditions (OLCD). The structure, hydrophobicity, and chemical composition of membranes showed differences regarding fouling on anion- (AEM) and cation- (CEM) exchange membranes facing the diluate and the concentrate, both for AW and ROAW. Furthermore, operating at OLCD tends to reduce fouling compared to ULCD, due to the expected generation of electroconvective vortices. 2D fluorescence spectroscopy and Fourier-transform infrared spectroscopy (FTIR) provided complementary and more detailed information regarding the fouling and efficiency of the cleaning procedure. The 2D fluorescence spectra showed that the AEM surfaces in contact with the diluate change more than those in contact with the concentrate. The FTIR analyses showed the presence of lactose and lactic acid on the AEM surfaces in contact with the concentrate, which could not be detected by fluorescence.

Effects of nanofiltration on desalination of flue gas desulfurization wastewater by electrodialysis: Treatment effect, fouling property and techno-economic analysis

This study seeks to compare the treatment effect and fouling property of the nanofiltration (NF) – electrodialysis (ED) hybrid system and single ED system, and launches a techno-economic analysis for the flue gas desulfurization wastewater treatment. The optimal operation conditions of ED and NF process were determined, and the fouling properties of NF membranes and ion exchange membranes (IEMs) were explored. Morphology and chemical structure analysis concluded that NF membranes are more susceptible to fouling than IEMs, ascribing to the discrepancy of driving force and fouling mechanisms. The economic impact of membrane fouling was calculated in detail, including costs of increased membrane resistance and pressure drop of feed channel, decreased water permeability, membrane replacement and cleaning-in-place (CIP). We have found that the major factor of increased operating cost resulting from fouling comes from the membrane replacement cost (≥66%), followed by additional energy cost (≥4.1%) and with only a minor contribution from the CIP costs (≥0.8%). Overall, the total operating cost for the NF-ED system was 35.9% more expensive than the single ED system with a total cost of 2.95 ¥/m3. The results can provide a useful reference for the application of membrane technology in water and wastewater treatment.

Comparative Study of Water Desalination using Reverse Osmosis (RO) and Electro-dialysis Systems (ED): Review

The increasing drinking water demand in many countries leads to an increase in the use of desalination plants, which are considered a great solution for water treatment processes. Reverse osmosis (RO) and electro-dialysis (ED) systems are the most popular membrane processes used to desalinate water at high salinity. Both systems work by separating the ionic contaminates and disposing of them as a brine solution, but ED uses electrical current as a driving force while RO uses osmotic pressure. A direct comparison of reverse osmosis and electro-dialysis systems is needed to highlight process development similarities and variances. This work aims to provide an overview of previous studies on reverse osmosis and electro-dialysis systems related to membrane module and design processes; energy consumption; cost analysis; operational problems; efficiency of saline removal; and environmental impacts of brine disposal. RO system uses osmotic pressure as a driving force to force water through the membrane with less energy than other desalination systems. The enhancements in membrane materials and power recovery of the unit have massively decreased the price of RO units. ED system uses an electrical current to push dissolved ions across ion exchange membranes. The results of this review showed that desalination plants must be integrated with renewable energy to reduce power consumption and costs related to energy. Various technologies, including treatment processes and disposal methods, must be used to control concentrated solutions resulting from desalination processes because 5 to 33% of the total cost of the desalination process is associated with brine disposal.

Current distribution along electrodialysis stacks and its influence on the current-voltage curve: behaviour from near-zero current to limiting plateau

The current maldistribution along the flow path of electrodialysis (ED) units is a well-known phenomenon. However, it has been poorly quantified via experimental tests so far. This work aimed at measuring the current distribution in an ED stack with 40 cm path length, provided with four-segment electrodes. The current-voltage curve (CVC) of each segment was recorded under several operating conditions of inlet concentrations and feed velocity. In the CVC of the first segment, the current increased approaching a saturation, while in that of the remaining segments it passed through a maximum and then settled at near-zero values when high voltage values were applied. The current fraction on the segments decreased from inlet to outlet. In the overall CVC's first region, up to ~50 % of total current flowed through the first quarter of stack. As the voltage increased, the current fraction increased in the first segment, while it decreased in the other ones tending to vanish. At the limiting condition, the relative standard deviation of the current fraction distribution ranged from 40 % to 68 %. This strong non-uniformity in the ED stack, which may represent one stage of an industrial plant, implies that the design of commercial units must be improved.

Preparation of a Monovalent-Selective Anion-Exchange Membrane: Effect of Alkyl Chain Length and Crystallinity

Crosslinked anion-exchange membranes (AEMs) with reasonable water uptake are used for the separation of monovalent anions from their mixture with bivalent anions by electrodialysis (ED). Herein, we report the preparation of a series of monovalent-selective crosslinked AEMs containing imidazole rings from the polyacrylonitrile-co-poly(vinylimidazole) (PAN-co-PVIm) copolymer (AN/VIm ratio = 75:25 mol/mol), followed by N-alkylation with alkyl halide of different chain lengths (carbon number: 1,6,10,18), followed by reaction with 1,6-diamino hexane. The difference in the obtained permselectivity (PSO42–Cl–) was compared with those of un-crosslinked and commercial Ionsep membranes. The effects of crosslinking, the chain length of the alkyl spacer attached to imidazolium nitrogen of the membrane matrix, and the partial crystallinity occurring due to the arrangement of long alkyl chains on PSO42–Cl– were investigated. A representative crosslinked membrane (MQ18) with an octadecyl alkyl chain length (C18) attached to the imidazole moiety exhibited moderate water uptake (22%), high fixed charge density (0.037 meq/cm3), and high PSO42–Cl– (6.4) during the separation of a mixture of 0.01 M sodium chloride and 0.01 M sodium sulfate (2000 mg/L) by the ED process. The PSO42–Cl– value is further increased from 6.4 to 16.7 by increasing the electrolyte concentration to 0.05 M sodium chloride and 0.05 M sodium sulfate. The rigid imidazolium structure, locally organized higher chain length of the alkylating group, and the crosslinked network structure provide steric hindrance for the passage of more hydrophilic sulfate anions, which facilitates higher selectivity.

Interplay between Forced Convection and Electroconvection during the Overlimiting Ion Transport through Anion-Exchange Membranes: A Fourier Transform Analysis of Membrane Voltage Drops

Electrodialysis (ED) applications have expanded in recent years and new modes of operation are being investigated. Operation at overlimiting currents involves the phenomenon of electroconvection, which is associated with the generation of vortices. These vortices accelerate the process of solution mixing, making it possible to increase the transport of ions across the membranes. In this work, frequency analysis is applied to investigate the interaction between different parameters on the development of electroconvection near anion-exchange membranes, which would provide a basis for the development of ED systems with favored electroconvection. Chronopotentiometric curves are registered and Fast Fourier Transform analysis is carried out to study the amplitude of the transmembrane voltage oscillations. Diverse behaviors are detected as a function of the level of forced convection and current density. The synergistic combination of forced convection and overlimiting currents leads to an increase in the signal amplitude, which is especially noticeable at frequencies around 0.1 Hz. Fast Fourier Transform analysis allows identifying, for a given system, the conditions that lead to a transition between stable and chaotic electroconvection modes.

Investigation of Histamine Removal by Electrodialysis from the Fermented Fish Sauce and Its Effects on the Flavor.

Histamine is one of the most concerned safety indicators in fish sauce. Considering its charge property, electrodialysis (ED) was used to control the histamine in fish sauce, and studies were focused on three operating parameters: input current, pH, and flow velocity. A Box-Behnken design and response surface methodology was adopted to derive a statistical model, which indicated that 5.1 A input current, pH 3.8, and 40 L∙h-1 flow velocity were optimal operation conditions. Under this condition, the histamine removal rate reached 53.41% and the histamine content met the allowable histamine limit of below 400 mg·kg-1 in fish sauce, while the amino nitrogen (ANN) loss rate was only 15.46%. In addition, amino acids and volatile compounds changed differently during ED. As a result, with decreased histamine, the fish sauce after ED was also less salty and less fishy. The study first explored utilizing ED to remove histamine from fish sauce, which has positive implications for promoting the safety of aquatic products.

Recovery and upcycling of residual lactic acid and ammonium from biowaste into yeast single cell protein

The yeast Saccharomyces cerevisiae is a potential candidate for converting waste resources into food-grade single cell protein (SCP). Food waste fermentation broth rich in lactic acid was tested as an alternative substrate source for S. cerevisiae in this study. An electrodialysis (ED) system was developed to recover lactate, acetate and ammonium ions (La-, Ac- and NH4+) from the broth. First, we evaluated the system resilience under various volatile fatty acids (VFAs) and pH levels. Initial acetate and lactate concentrations did not affect La- and Ac- recovery efficiencies but affected their ion fluxes and competitive ion transport. The migration of La- was delayed by increasing the initial acetate concentration, while Ac- migration was not affected by lactate concentrations. Increasing the broth pH reduced competitive H+ ions and thus improved the NH4+ recovery efficiency. Further, broth recirculation and pH control were examined to identify potential challenges associated with continuous flow in real-life applications. Recirculation caused a greater loss of recovered Ac- and NH4+ over the extended period. The pH control decreased VFAs recovery efficiencies because VFAs could not fully dissociate in the dilute, and more VFAs were lost in the concentrate. Finally, the recovery from lactate-rich fermentation broth was used as yeast substrate and contributed to a robust SCP yield of 0.62 g/g-C. Manufacturing one kilogram of SCP costs €6-10 in electricity and €3-6 in raw material. This study provides a better understanding of competitive ion transport during ED and uncovers potential biowaste resources for sustainable SCP production.

Removal of heavy metals from fly ash using electrodialysis driven by a bioelectrochemical system: a case study of Pb, Mn, Cu and Cd

ABSTRACT Municipal solid waste incineration (MSWI) fly ash is classified as hazardous waste due to high leachable heavy metals, and incineration leachate belongs to organic wastewater with high biodegradability. Electrodialysis (ED) has shown potential for the removal of heavy metals from fly ash, and bioelectrochemical system (BES) employs biological and electrochemical reactions to generate electricity and remove contaminants from a wide range of substrates. In this study, the ED-BES coupled system was constructed for the co-treatment of fly ash and incineration leachate, where the ED was driven by BES. The treatment effect of fly ash by varying additional voltage, initial pH and liquid-to-solid (L/S) ratio was evaluated. Results showed that the highest removal rates of Pb, Mn, Cu and Cd were 25.43%, 20.13%, 32.14% and 18.87% after 14 days treatment of the coupled system, respectively. These values were obtained under 300 mV of additional voltage, L/S 20 and initial pH3. After the treatment of the coupled system, the fly ash leaching toxicity was lower than the threshold of GB5085.3-2007. The highest energy saving for removed Pb, Mn, Cu and Cd were 6.72, 15.61, 8.99 and 17.46 kWh/kg, respectively. The ED-BES can be considered a cleanliness approach to treating fly ash and incineration leachate simultaneously.

Developmental Progress of Electrodialysis Technologies and Membrane Materials for Extraction of Lithium from Salt Lake Brines

Salt lake brines have become the main source of lithium owing to their abundant reserves and low extraction costs. The low absolute concentration of Li+ and the complexity of accompanying ions in the brines are crucial issues, thereby inspiring the development of a variety of lithium extraction technologies. Among them, electrodialysis (ED) enables acceptable separation performance, reduced energy consumption, and near-zero pollution toward salt lake brines with a high Mg2+/Li+ mass ratio. Most recently, the rapid advancement of integrated ED technologies and emerging strategies for membrane material fabrications are conducive to facilitating the implementation of this technology. The newly proposed processes can achieve higher energy utilization and enhance the concentration of lithium salt products. For membrane materials, the superior permselectivity between lithium and magnesium is still the current pursuit. The key metrics for developing membranes involve tuning the materials’ hydrophilicity, pore size, and charge. Among them, due to the rise of lithium-specific recognition materials, it is believed that coupling them with ED technology to achieve efficient and precise extraction of lithium will be the future development direction.

Development of the Miniature Robotic Electrodialysis (MR ED) System for Small‐Scale Desalting of Liquid Samples With Recovery of Organics

AbstractWhile liquid environments with high salt content are of broad interest to the Earth and Planetary Science communities, instruments face challenges in detecting organics in hypersaline samples due to the effects of salts. Therefore, technology to desalt samples before analysis by these instruments would be enabling for liquid sampling on missions to Mars or ocean worlds. Electrodialysis (ED) removes salt from aqueous solutions by applying an electric potential across a series of ion‐selective membranes, and is demonstrated to retain a significant percentage of dissolved organic molecules (DOM) in marine samples. However, current electrodialysis systems used for DOM recovery are too large for deployment on missions or for use in terrestrial fieldwork. Here, we present the design and evaluation of the Miniature Robotic Electrodialysis (MR ED) system, which is approximately 1/20th the size of heritage instruments and processes as little as 50 mL of sample at a time. We present tests of the instrument efficiency and DOM recovery using lab‐created solutions as well as natural samples taken from an estuary of the Skidaway River (Savannah, GA) (Verity, 2002) and from South Bay Saltworks (San Diego, CA) (Roseman & Watry, 2008; Survey, 2011). Our results show that the MR ED system removed 97%–99% of the salts in most samples, with an average DOC recovery range from 53% to 77%, achieving similar capability to tabletop instruments. This work both demonstrates MR ED as a possible field instrument and increases the technology readiness level of miniaturized electrodialysis systems for future missions.

Synergistically enhancing the antibacterial and antibiofilm activities of anion exchange membrane by chemically assembling gentamicin and N-chloramine layers

Biofouling is one of significant obstacles decaying the high separation performance and long-term stability of polymer membranes during the application. To explore the desirable anti-biofouling anion exchange membrane (AEM), in this work, a series of modified AEMs having surface antibacterial functional layers on surface has been prepared by using gentamicin and N-chloramine for electrodialysis (ED). The antibacterial functional layer on surface was constructed via chemical assembly. By using CuSO4 and H2O2 as the trigger, l-dopa was oxidized on surface of commercial AEM (Fuji type II) to form a carboxyl layer. Thereafter, gentamicin was chemically assembled via the amide condensation reaction. It was chlorinated with diluted NaClO solution to endow it with synergistic antibacterial activity by using gentamicin. Investigation demonstrates that the optimized membrane of P(l-Dopa)@GM-Cl has high antibacterial activity against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Among them, flow cytometry shows that the antibacterial rate of P(l-Dopa)@GM-Cl against E. coli is more than 99%, which is much higher than original membrane (28.4%). P(l-Dopa)@GM-Cl exhibits the enhanced performance in inhibiting biofilm observed by scanning electron microscopy analysis. This work may provide a reference for the construction of anti-biofouling ion exchange membrane.

Electrodialysis Processes an Answer to Industrial Sustainability: Toward the Concept of Eco-Circular Economy?-A Review.

Wastewater and by-product treatments are substantial issues with consequences for our society, both in terms of environmental impacts and economic losses. With an overall global objective of sustainable development, it is essential to offer eco-efficient and circular solutions. Indeed, one of the major solutions to limit the use of new raw materials and the production of wastes is the transition toward a circular economy. Industries must find ways to close their production loops. Electrodialysis (ED) processes such as conventional ED, selective ED, ED with bipolar membranes, and ED with filtration membranes are processes that have demonstrated, in the past decades and recently, their potential and eco-efficiency. This review presents the most recent valorization opportunities among different industrial sectors (water, food, mining, chemistry, etc.) to manage waste or by-product resources through electrodialysis processes and to improve global industrial sustainability by moving toward circular processes. The limitations of existing studies are raised, especially concerning eco-efficiency. Indeed, electrodialysis processes can be optimized to decrease energy consumption and costs, and to increase efficiency; however, eco-efficiency scores should be determined to compare electrodialysis with conventional processes and support their advantages. The review shows the high potential of the different types of electrodialysis processes to treat wastewaters and liquid by-products in order to add value or to generate new raw materials. It also highlights the strong interest in using eco-efficient processes within a circular economy. The ideal scenario for sustainable development would be to make a transition toward an eco-circular economy.

Carbon footprint analysis and carbon neutrality potential of desalination by electrodialysis for different applications

Low-carbon water production technologies are indispensable for achieving sustainable development goals and mitigating global climate change. However, at present, many advanced water treatment processes lack a systematic assessment of related greenhouse gas (GHG) emissions. Thus, quantifying their life-cycle GHG emissions and proposing strategies toward carbon neutrality is urgently needed. This case study focuses on electrodialysis (ED), an electricity-driven desalination technology. To analyze the carbon footprint of ED desalination in various applications, a life cycle assessment model was developed based on industrial-scale ED processes. For seawater desalination, the carbon footprint is 59.74 kg CO2-eq/metric ton removed salt, which is one order of magnitude lower than that of high-salinity wastewater treatment and organic solvent desalination. Meanwhile, the power consumption during operation is the main hotspot of GHG emissions. Power grid decarbonization and improved waste recycling in China are projected to reduce the carbon footprint up to 92%. Meanwhile, the contribution of operation power consumption is expected to reduce from 95.83% to 77.84% for organic solvent desalination. Through sensitivity analysis, significant non-linear impacts of process variables on the carbon footprint were determined. Therefore, it is recommended to optimize the process design and operation to reduce power consumption based on the current fossil-based grid. GHG reduction for module production and disposal should also be emphasized. This method can be extended to general water treatment or other industrial technologies for carbon footprint assessment and reducing GHG emission.

Molecular composition and chemodiversity of dissolved organic matter in wastewater sludge via Fourier transform ion cyclotron resonance mass spectrometry: Effects of extraction methods and electrospray ionization modes

High-resolution mass spectrometry was extensively applied in molecular composition and transformation pathways of dissolved organic matter (DOM) in wastewater sludge treatments. Sample pretreatment methods and electrospray ionization (ESI) modes significant affect the accuracy of molecular characterization for DOM. This study investigated the effects of pretreatment methods (styrene divinyl benzene polymer (PPL), octadecyl (C18), and electrodialysis (ED)) on molecular characteristics of DOM in two typical wastewater sludges (waste activated sludge (WAS) and anaerobic digestion sludge (ADS)) analyzed by FT-ICR MS in both positive ESI (ESI (+)) and negative ESI (ESI (−)) modes. The results indicated that ED pretreatment exhibited the highest recovery rate of 70% ‒ 95% for sludge-derived DOM. ED and PPL performed well in recovering the different sludge-derived DOM with a high similarity of molecular characteristics (e.g., lipids, proteins/aliphatic, and lignins/CRAM-like), and the C18 method was ineffective in extracting carbohydrates, unsaturated hydrocarbons, and amino sugars. In addition, compared with single ESI (−) analysis mode, the molecular number identified by ESI (+) analysis mode was increased by 200%, especially, more unsaturated hydrocarbons and N-containing compounds were detected. Except for biogenic DOM, plenty of emerging containments (ECs) in sludge-derived DOM were identified; ESI (−) mode was more effectively in recognizing the alkyl benzene sulfonic acids (e.g., anionic surfactants); and ESI (+) mode was more effectively for plasticizers identification, for example, dioctyl terephthalate and dibutyl phthalate. This study illustrated that ED pretreatment coupled with FT-ICR MS in dual ESI modes could give more insights in complexed molecular information for DOM in wastewater sludge, and provides a theoretical basis for subsequent sludge treatments and disposals.

Application of Membrane Processes for Nitrate (NO3-) Removal

Background: The primary sources of nitrate contamination in groundwater resources are excessive fertilizer use and unregulated land discharges of treated wastewater. Due to its harmful nature to human health and its contribution to eutrophication, the removal of nitrate from water has been of great interest in the last decades. Various techniques, such as adsorption, ion exchange, catalytic and biological denitrification, and membrane processes, have been applied for NO3 - removal. Objective: In this review study, the removal of NO3 - by membrane processes, including electrodialysis (ED), electrodeionization (EDI), reverse osmosis (RO), and ultrafiltration, has been reviewed. Method: The pressure-driven membrane and electro-membrane processes applications to NO3 - removal have been reviewed. Results: The effects of process parameters, interferences, and limitations of membrane processes have been summarized. Conclusion: Membrane processes could be a promising alternative for NO3 - removal. After suitable membrane preparation/modification, the nitrate removal rate could reach >99%.