Bipolar Membrane Electrodialysis Process Research Articles

Desalination of mother liquor generated from the precipitation of lithium carbonate during the recycling of retired lithium ion battery

Generally, hydrometallurgy process is adopted in factory to recover valuable metal from anode materials in lithium ion battery. The mother liquor generated from the precipitation of lithium carbonate in this process is often managed by evaporative crystallization process which is high energy-consuming and expensive. The methodology employed in this research involves pretreatment and bipolar membrane electrodialysis to partition salts within the mother liquor into acids and bases, thereby achieving cost savings. The findings reveal that a significant 76.5 % reduction in COD is achievable through the application of potassium permanganate and activated carbon in the treatment of the mother liquor. Subsequently, the treated mother liquor can be transfer to electrodialysis process for further treatment. During this process, desalination of the mother liquor occurs, leading to the decomposition of sodium sulfate into sulfuric acid and sodium hydroxide. Analysis of the experimental data reveals that optimizing the initial concentrations of sulfuric acid and sodium hydroxide within the acid and alkali collection chambers, along with the application of elevated electric current density and maintaining a high pH value of the mother liquor, yields improvements in current efficiency and concomitant reductions in energy consumption. Under optimal conditions, the current efficiency of acid and alkali preparation is 52.53 % and 62.12 % respectively, along with energy consumption of acid and alkali preparation is 8.68kWh/kg and 8.99kWh/kg respectively. The pretreatment and bipolar membrane electrodialysis process is low-energy consumption and inexpensive, facilitating a reduction in processing expenses to $6.659 per ton of mother liquor.

Recovery of ammonia nitrogen from simulated reject water by bipolar membrane electrodialysis

ABSTRACT Ammonia monohydrate (NH3·H2O) is an important chemical widely used in industrial, agricultural, and pharmaceutical fields. Reject water is used as the raw material in self-built bipolar membrane electrodialysis (BMED) to produce NH3·H2O. The effects of electrode materials, membrane stack structure, and operating conditions (current density, initial concentrations of the reject water, and initial volume ratio) on the BMED process were investigated, and the economic costs were analyzed. The results showed that compared with graphite electrodes, ruthenium-iridium-titanium electrodes as electrode plates for BMED could increase current efficiency (25%) and reduce energy consumption (26%). Compared with two-compartment BMED, three-compartment BMED had a higher ammonia nitrogen conversion rate (86.6%) and lower energy consumption (3.5 kW· h/kg). Higher current density (15 mA/cm2) could achieve better current efficiency (79%). The BMED performances were improved when the initial NH 4 + concentrations of the reject water increased from 500 mg NH 4 + /L to 1000 mg NH 4 + /L, but the performance decreased as the concentration increased from 1000 mg NH 4 + /L to 1500 mg NH 4 + /L. High initial volume ratio of the salt compartment and product compartment was beneficial for reducing energy consumption. Under the optimal operating conditions, only 0.13 $/kg reject water was needed to eliminate the environmental impact of reject water accumulation. This work indicates that BMED can not only achieve desalination of reject water, but also generate products that alleviate the operational pressure of factories.

Optimizing Operational Parameters for Lithium Hydroxide Production via Bipolar Membrane Electrodialysis

Traditional lithium hydroxide production techniques, like lithium sulfate and lithium carbonate causticizing methods, suffer from drawbacks including high specific energy consumption, time-consuming processes, and low recovery rates. The conversion of lithium chloride to lithium hydroxide using bipolar membrane electrodialysis is straightforward; however, the influence of operational parameters on bipolar membrane electrodialysis performance have not been investigated. Herein, the impact of the current density (20 mA/cm2~80 mA/cm2), feed concentration (0.5 M~2.5 M), initial feed pH (2.5, 3.5 and 4.5), and the volume ratio of the feed and base solution (1:1, 2:1 and 3:1) on the current efficiency and specific energy consumption in the bipolar membrane electrodialysis was systematically investigated. The bipolar membrane electrodialysis process showed promising results under optimal conditions with a current density of 50 mA/cm2 and an initial lithium chloride concentration of 1.5 M. This process achieved a current efficiency of 75.86% with a specific energy consumption of 3.65 kwh/kg lithium hydroxide while also demonstrating a lithium hydroxide recovery rate exceeding 90% with a purity of about 95%. This work will provide valuable guidance for hands on implementation of bipolar membrane electrodialysis technology in the production of LiOH.

Effects of cell configuration and bipolar membrane on preparation of LiOH through bipolar membrane electrodialysis from salt lake brine

Bipolar membrane electrodialysis (BMED) is a promising process to prepare LiOH from the salt lake brine. Revealing the effects of the cell configuration and property of bipolar membrane (BM) on the mass transfer and current efficiency of BMED is crucial to promote its industrial application. Herein, two-compartment (C-B) and three-compartment (A-C-B), and three types of BMs (FBM, BP-1, and TWBP1) were systematically studied. Results show that three-compartment is superior to two-compartment, as the latter could restrain electromigration of Li+, enable recombination of H+ and OH–, and lead to lower current efficiency. Among three BMs, TWBP1 has highest current efficiency, while BP-1 can prepare LiOH solution with least impurity ions. To reveal the influencing mechanism of the BMs’ properties on the electromigration of Li+ and co-ions leakage, CVC curves and chronopotentiograms were detailly investigated. Results show that the higher energy consumption of BP-1 may be attributed to its highest specific resistivity, while its better co-ions selectivity is beneficial to prepare acid/base solutions with lesser impurities, indicating that effects of the specific resistivity and selectivity of BMs on BMED process for producing LiOH from salt lake brine is an important “trade-off” relationship needing to be balanced to realize the higher current efficiency and higher quality products.

Improving ammonia nitrogen removal and recovery by BMED stack optimization: The effect of ion exchange membrane thickness

Bipolar membrane electrodialysis (BMED) has emerged as an efficient and promising technology for the removal and recovery of ammonia nitrogen. Despite its potential, the optimization of BMED systems for enhanced performance and energy efficiency remains a critical challenge, particularly in the context of varying ion exchange membrane (IEM) thicknesses. Membranes with a thickness of < 80 µm have low resistance and are mainly used for processes requiring low energy consumption. Membranes with a thickness of 80–250 µm have moderate resistance and high ion selectivity and are widely used for electrodialysis applications. Membranes with a thickness of > 250 µm have higher ion selectivity than commercial membranes with a thickness of 80–250 µm and are suitable for processes that demand high purity. This study investigates the effect of IEM thickness ranging from 16–400 µm on BMED performance for ammonia nitrogen removal and recovery, and energy consumption. The BMED configuration comprising five cell triplets consisting of a cation exchange membrane, bipolar membrane, and anion exchange membrane was employed. The thickness of IEMs was divided into three categories: 16–17 µm (PCEM/ PAEM), 100–150 µm (CD100/AD100, InnoSep-C/InnoSep-A), and 380–400 µm (MC-3470/MA-3475). In membranes with a thickness of 100–150 µm, the ammonia nitrogen removal was exceptionally high at 99.2 %, with a recovery of 98.7 % (CD100/AD100: 100 µm) at a current density of 80 mA/cm2, and the system exhibited low specific energy consumption (SEC) of 8.87 kWh/kg-N (InnoSep-C/InnoSep-A: 150 µm) at a current density of 20 mA/cm2. However, when using the thinnest IEMs (PCEM: 16 µm, PAEM: 17 µm), an increase in total ammonia nitrogen loss (10.21–22.01 %) led to a reduction in ammonia nitrogen recovery. Conversely, when using the thickest IEMs (MC-3470: 380 µm, MA-3475: 400 µm), the SEC was extremely high (30.98–126.67 kWh/kg-N), making them unsuitable for the BMED process for ammonia nitrogen removal and recovery. Based on these experimental results, it is suggested to use an optimal thickness of IEM within the range of 80–250 µm in the BMED systems to achieve a balanced performance, maximizing ammonia nitrogen removal and recovery while minimizing the SEC. Consequently, the present study provides a comprehensive understanding of the effects of the IEM thicknesses on the BMED systems and could offer a practical perspective for optimizing the BMED stack with respect to improving the removal and recovery rate of ammonia nitrogen and reducing the energy consumption.

Heavy Metal Removal from Aqueous Solutions Using a Customized Bipolar Membrane Electrodialysis Process.

Lack of safe water availability and access to clean water cause a higher risk of infectious diseases and other diseases as well. Heavy metals (HMs) are inorganic pollutants that cause severe threats to humans, animals, and the environment. Therefore, an effective HM removal technology is urgently needed. In the present study, a customized bipolar membrane electrodialysis process was used to remove HMs from aqueous solutions. The impacts of the feed ionic strength, applied electrical potential, and the type and concentration of HMs (Cd2+, Co2+, Cr3+, Cu2+, and Ni2+) on the process performance were investigated. The results showed that feed solution pH changes occurred in four stages: it first decreased linearly before stabilizing in the acidic pH range, followed by an increase and stabilization in the basic range of the pH scale. HM speciation in the basic pH range revealed the presence of anionic HM species. The presence of HMs on anion exchange membranes confirmed the contribution of these membranes for HM removal in the base channels of the process. While no clear trend was seen in the ionic strength solution, the maximum HM removal was observed when 1.5 g/L NaCl was used. The initial HM concentration showed a linear increase in HMs removal of up to 30 mg/L. A similar trend was seen with an increase in the applied electrical potential of up to 15 V. In general, the amount of HMs removed increased in the following order: Cd2+ ˃ Ni2+ ˃ Co2+ ˃ Cu2+ ˃ Cr3+. Under some operational conditions, however, the removed amount of Cu2+, Co2+, and Ni2+ was similar. The mass balance and SEM-EDX results revealed that the removed HMs were sorbed onto the membranes. In conclusion, this process efficiently separates HMs from aqueous solutions. It showed the features of diluate pH adjustment, reduction in the overall stack electrical resistance, and contribution of anion exchange membranes in multivalent cation removal. The mechanisms involved in HMs removal were diffusion and migration from the bulk solution, followed by their sorption on both cation and anion exchange membranes.

Recovery of triethylamine and phosphoric acid from wastewater using a novel hybrid process of bipolar membrane electrodialysis and resin adsorption

Triethylammonium phosphate wastewater, resulting from the absorption of triethylamine (TEA) exhaust gas by phosphoric acid, poses challenges in environmental protection. In this study, a novel combined process of bipolar membrane electrodialysis (BMED) and resin adsorption (RA) was proposed. Under the optimal conditions of 50 mA/cm2 and 5 cm/s, more than 96 % of the triethylammonium phosphate in real wastewater was converted into TEA and phosphoric acid during the BMED processes. Its current efficiency of 47 % and an energy consumption rate of 4.26 kWh/kg TEA. Furthermore, the low-concentration wastewater from BMED could be effectively treated through D001 resin at pH 2. Desorption of TEA loaded on D001 resin could be achieved using a 6 wt% phosphoric acid produced from the BMED process, and the concentrated desorption solution could be reprocessed through BMED process. The effluent of RA process could undergo chemical precipitation, thereby contained 18 mg/L COD, 0.43 mg/L TP and less than 3 mg/L TEA, meeting the first-class A standard of the Chinese “GB18918-2002 Discharge standard of pollutants for municipal wastewater treatment plant”. This novel strategy offered an innovative and environmentally friendly method for recycling this type of wastewater within ecological industries.

A closed-loop integrated process of bipolar membrane electrodialysis and resin adsorption for resource recovery from high-salinity phenolic wastewaters: Salicylic acid manufacturing wastewater as a representative

Phenolic compounds stand as consequential chemical precursors, boasting an extensive array of industrial applications. The worldwide yield of such compounds attained 17 million tons annually, and a substantial volume of effluent characterized by elevated phenolics content along with inorganic salinity was emanated from the manufacturing processes, which would exert profound deleterious impacts upon the ecosystem and aquatic environment. Scant literature was available regarding efficacious treatment of these high-salinity phenolic wastewaters and complete recovery of its constituents currently. In this study, initially, various high-salinity phenolic wastewaters were treated in bipolar membrane electrodialysis (BMED) system, and the migration behavior of constituents was investigated. Drawing upon the migration patterns and the efficacy of BMED, a closed-loop integrated process of BMED and resin adsorption was proposed to thoroughly address this kind of wastewater and attain comprehensive material reclamation. Because of the wide use of salicylic acid (SA) all over the world, the enormous production in China, and the complexity of the sewage which contained rich Na2SO4, phenol, and SA from manufacturing process, SA manufacturing wastewater was selected as the representative sample. For the BMED process, the desalination rate got 99.4 % under the optimum conditions. The concentrations of H2SO4 and NaOH obtained were 0.56 and 0.78 mol/L. The preliminary separation of phenol and SA was realized during desalination. Then, the effluent of BMED feed compartment was injected into two-stage resin unit. The satisfactory regeneration of both spent resins was achieved, and high-purity phenol and SA were obtained. No contaminants were undetected in the effluent, allowing for the reuse of the effluent within BMED. The complete resource utilization of SA manufacturing wastewater was realized, indicating the viability of proposed integrated process for treating and resource recovering of analogous high-salinity industrial phenolic wastewater.

Treatment of carbocysteine wastewater by bipolar membrane electrodialysis: From lab-to pilot-scale

Carbocysteine (H2ccys) wastewater, which contains H2ccys, chloroacetic acid, and ammonium chloride, can pose significant risks to the environment. In this study, a novel strategy was proposed for treating H2ccys wastewater by bipolar membrane electrodialysis (BMED) to realize resource recovery. The migration and coexistence mechanism of organic/inorganic ions in wastewater were investigated in lab-scale experiments. The results indicated that the desirable migration of inorganic ions, such as NH4+ and Cl− ions, in the feed compartment were dominant. The undesirable migration of organic molecules, such as ClCH2COOH and H2ccys, could be managed through precise control of the BMED reaction process. To optimize the energy efficiency and thermal effect occurred in the pilot-scale, a two-stage BMED process was designed for treating H2ccys wastewater. The results revealed that BMED produced 1.33–1.63 M of HCl and 2.62–2.88 M of NH3·H2O, and removed 90 wt% of NH4Cl from H2ccys wastewater. Meanwhile, the thermal effect of the slot at the outermost acid compartment decreased from 3.32 W in the one-stage BMED process to 0.10 W in the two-stage BMED process during the pilot-scale tests. The current efficiency of the two-stage BMED process for the acid/base production and feed desalination in the pilot-scale tests increased and its energy consumption decreased compared with the lab-scale tests. Moreover, the BMED rrecycling route showed that a closed loop can be realized in the treatment of H2ccys wastewater, and its economic assessment showed that applying BMED to the treatment of H2ccys wastewater have economic benefits. These findings illustrated the feasibility of this novel strategy for treating H2ccys wastewater and laid a solid foundation for its industrialization.

Techno-economic analysis of integrated bipolar membrane electrodialysis and batch reverse osmosis for water and chemical recovery from dairy wastewater

Bipolar membrane electrodialysis (BMED) for acid and base recovery and batch reverse osmosis (BRO) for water recovery are analyzed technically and economically as a dairy wastewater treatment solution. The proposed process layouts also aimed to utilize recovered water and chemical within same industrial plant. The hybridization of BMED with BRO process is used to reduce capital and operating cost of BMED unit and compared with the standalone BMED process. The analysis reveals that the hybridization of BRO-BMED system achieve 25.8% less unit cost and three times higher concentration of acid and base chemicals compare to standalone system. The comparison of system is done at optimum current density of BMED process and permeate flux of BRO process. Sensitivity analysis of permeate flux, current density and feed salinity is carried out. The higher feed concentration is desirable and reduces the cost in BMED process and same with current density but up to 409 and 255 A/m2 in hybrid and standalone system respectively. In hybrid system, the multi-response surface analysis observes that higher permeate flux in BRO reduces the BMED cost but increases the BRO cost and the minimum cost of 14 USD/kmol is achieved at 26 LMH permeate flux.

Ion migration characteristics during the bipolar membrane electrodialysis treatment of concentrated reverse osmosis brine

Bipolar membrane electrodialysis (BMED) plays a unique role in liquid phase mass transfer and acid-alkali preparation, so BMED wastewater treatment and reuse applications are attracting increasing attention. Herein, BMED was used to treat the concentrated brine (ROC) produced during reverse osmosis (RO), recover valuable resources and produc acid and alkali. The effects of voltage, feed concentration ratio (FCR), and flow velocity on ion flux during BMED were systematically surveyed, and unusual phenomena were thoroughly analyzed during ion transport. The results showed that the main driving force for ion transport was operating voltage, a critical parameter determining operating time. Concentration polarization and concentration gradient caused by a high feed concentration significantly affected ion electromigration stability, and ion hydration characteristics were nonnegligible factors determining ion transport speed. Flow velocity had no marked impact on the experimental outcomes. Furthermore, water transport occurred with salt ions during liquid-phase mass transfer. Under the optimal operating conditions (voltage 24 V, FCR 2:1, flow velocity 55 L/h), the BMED system showed excellent, continuous and stable operation, and efficient production of mixed acid (0.88 mol/L) and mixed alkali (0.72 mol/) was achieved. The BMED process cost was 10.537 yuan/kg NaOH; therefore, process applications of BMED are economically feasible.

Power-free bipolar membrane electrodialysis for acid-alkali production in river estuaries

Recent studies suggest that 2–2.6 TW blue energy can be harvested by mixing coastal seawater with freshwater world widely, but the extractable part was limited due to undesired development of conversion techniques. In this study, a novel power-free bipolar membrane electrodialysis process is proposed for the closed-loop utilization of salinity gradient energy and the salt resources in seawater. The system was evaluated using theoretical and experimental methods. Significance of the various membrane modules and operational conditions was evaluated. Based on fluid dynamics simulations and fluid online imaging technologies, a prototype electro-membrane reactor was fabricated to maximize the achievable energy and acid/base products. The acid production rate reached 6.9 mmol h−1 when feeding simulated seawater (30 g/L NaCl) and river water (1 g/L NaCl). The protocols provided in this work offer an effective route for developing advanced membrane processes for the harvesting of salinity gradient energy and acid-alkali production.

Modeling and Validation of a LiOH Production Process by Bipolar Membrane Electrodialysis from Concentrated LiCl.

Electromembrane processes for LiOH production from lithium brines obtained from solar evaporation ponds in production processes of the Salar de Atacama are considered. In order to analyze high concentrations' effect on ion exchange membranes, the use of concentrated LiCl aqueous solutions in a bipolar membrane electrodialysis process to produce LiOH solutions higher than 3.0% by mass is initially investigated. For this purpose, a mathematical model based on the Nernst-Planck equation is developed and validated, and a parametric study is simulated considering as input variables electrolyte concentrations, applied current density, stack design, process design and membrane characteristics. As a novelty, this mathematical model allows estimating LiOH production in a wide concentration range of LiCl, HCl and LiOH solutions and its effect on the process, providing data on final LiOH solution purity, current efficiency, specific electricity consumption and membrane performance. Among the main results, a concentration of 4.0% to 4.5% by LiOH mass is achieved, with a solution purity higher than 95% by mass and specific electrical energy consumption close to 4.0 kWh/kg. The work performed provides key information on process sensitivity to operating conditions and process design characteristics. These results serve as a guide in the application of this technology to lithium hydroxide production.

Separation of lithium chloride from ammonium chloride by an electrodialysis-based integrated process

Li+ and NH4+ have the same charge, valence, and similar ionic hydration radii. Hence, it is challenging to separate them through individual electrodialysis. Herein, an electrodialysis (ED)-based integrated process is proposed to separate Li+ from the mixed solution of LiCl and NH4Cl and simultaneously generate a concentrated LiOH solution. First, bipolar membrane electrodialysis (BMED) converts the mixed solution into the alkali solution of LiOH and NH3·H2O. The BMED performance was investigated by varying the operating parameters. The results show that the BMED membrane stack with the BP-A-C configuration performs better than the one with the BP-C configuration. A solution of 2.16 mmol/L LiOH and 0.05 mol/L NH3·H2O, selected as the initial alkali solution for the alkali tank, can reduce the energy consumption from 88.51 to 83.45 kW·h/kg, and improve the current efficiency from 53.45% to 56.69% slightly. Reducing the initial volume ratio of the alkali solution to the feed can concentrate the generated alkali solution and increase the LiOH conversion ratio simultaneously. Furthermore, reducing the initial feed concentration can efficiently improve the BMED performance. A maximum LiOH conversion ratio of 97.10% can be achieved in the BMED process. Second, ammonia removal with direct air stripping (AR-DAS) process is performed on the mixed alkali solution of LiOH and NH3·H2O to remove the ammonia and obtain the pure LiOH solution. The results show an ammonia removal ratio of more than 99%. Third, conventional electrodialysis (CED) concentrates the LiOH solution. Effects of the applied voltages and initial LiOH solution concentrations on the CED performance were investigated. The results show that a higher applied voltage increases energy consumption, while a higher initial LiOH solution concentration improves the LiOH concentration ratio. A maximum LiOH concentration ratio of 2.19 can be achieved in the CED process. Moreover, through analysis, the final solid products, generated by evaporation and crystallization, are LiOH·H2O crystals with the purity of 94.3 ± 3.56%. This work suggests that the ED-based integrated process is a highly effective approach to separating the mixed salt solutions of Li+ and NH4+.

Treatment of 2-Mercapto-5-methyl-1,3,4-thiadiazole (MMTD) wastewater by bipolar membrane electrodialysis: MMTD migration, process factors and implications

2-Mercapto-5-methyl-1,3,4-thiadiazole (MMTD), an important intermediate of widely used cefazolin and cefazedone antibiotics, was hardly decyclized during conventional wastewater treatment, raising a great risk to the environment. In this study, a new strategy for treating MMTD wastewater at the source by bipolar membrane electrodialysis (BMED) was proposed, realizing a material closed loop in the processes of MMTD production. Meanwhile, a laboratory-scale BMED system was set up for exploring MMTD migration, process factors, and technology implications. The results revealed that MMTD in the feed compartment may migrate into the acid/base compartment by electromigration and diffusion, the electromigration process of MMTD microspecies was controlled by its ionization, and the diffusion process of MMTD microspecies was influenced by its chemical potential on both sides of the membranes and the types of membranes. The analysis of the BMED process factors showed that these factors such as the initial pH of the feed solution, current density, flow velocity, and initial acid/base concentration affected the acid/base concentration, MMTD leakage, current efficiency, energy consumption, electric field intensity, ion flux, electrical resistance, head loss, and proton leakage. Based on these effects of the BMED process factors, some new strategies were proposed to optimize BMED process. Besides, the implications of BMED technology were affirmed by surveying the feasibility of BMED product recycling. Furthermore, this type of new strategy could be applied to the treatment of other similar wastewater at the source, realizing a closed loop in its production.

Impact of Phenol on Membranes during Bipolar Membrane Electrodialysis for High Salinity Pesticide Wastewater Treatment

To achieve a cleaner production, pesticide wastewater with concentrated NaCl can be treated by using a bipolar membrane electrodialysis (BMED) and converted to NaOH and HCl, which minimizes acid and alkali consumption in a pesticide production process. However, ion-exchange membranes (IEMs) are vulnerable to fouling by phenolic substances present in the concentrated NaCl solutions. This work aimed to understand the performance and fouling mechanism of BMED from phenol during the desalination of NaCl and explore an effective cleaning method. The results firstly showed that for the NaCl solutions with higher phenol concentrations, the selectivity of the IEMs was reduced after processing six successive batches of BMED, which led to reverse migration of ions, organics leakage, and an obvious increase in the energy consumption and the concentration of generated acid and alkali. Secondly, IEMs characterization analysis detected that the structure of the IEMs was deformed, while phenol fouling deposits were observed on the surface and interior of the IEMs, especially for the anion exchange membranes (AEMs). Then, the results of soaking tests proved that the phenol could bring about swelling-like degradation to the AEMs and 0.1 wt.% NaOH solution was studied to be the optimized cleaning agent since the performance of the fouled IEMs in the short-running process could be recovered after 5 h of in situ cleaning that removed the phenol fouling deposits efficiently. Finally, the results of a long-running BMED operation treating NaCl solution containing 10 g/L phenol concentration showed that the IEMs were severely fouled, and the fouling was firstly due to the swelling-like mechanism during the initial 12 successive batches, and then should belong to the blockage-like mechanism during the following 20 successive batches. The seriously fouled IEMs could no longer be recovered even after a deep in situ cleaning. This research proves that under appropriate pretreatment or operating conditions, the BMED process is an alternative way of treating wastewater with high salinity and the presence of phenol molecules.

Efficiently combined technology of precipitation, bipolar membrane electrodialysis, and adsorption for salt-containing soil washing wastewater treatment

Wastewater of that washing of soil that results in concentrations of inorganic salts, toxic metals, chelating agents, and refractory dissolved organic matter may threaten the surrounding environment. Simultaneously, the removal of contaminants and the recovery of resources from this wastewater remain challenging. This study investigated the probability of a novel combined treatment (chemical precipitation + bipolar membrane electrodialysis (BMED) + activated carbon (AC) adsorption) on salt-containing soil washing wastewater treatment. The results showed that the proposed combined treatment could achieve proficient removal of heavy metals, inorganic salts, and total organic carbon (TOC) with low energy consumption (removal efficiency of heavy metals and inorganic salts > 94%; TOC removal > 58%). Meanwhile, the efficient recovery of acid and alkali could also be realized in the proposed treatment (acid-production rate = 7.76 ± 0.38 mmol/h and base-production rate = 5.47 ± 0.42 mmol/h at 50 mA/cm2). The mechanism result indicated that the chemical precipitation process could achieve high removal of heavy metals. Then, the BMED process induced an efficient separation of organic matter and inorganic salts. Accordingly, the AC adsorption process could efficiently remove organics. Preliminary economic evaluation results revealed that the combined process could proficiently treat the soil washing wastewater with economic viability. Together, these findings provide meaningful information for soil washing wastewater treatment with resource recovery.

Boric acid recovery in dilute during the desalination process in BMED system

Bipolar membrane electrodialysis (BMED) system allows the simultaneous desalination and acid and base production. Boric acid (H3BO3) and sodium chloride (NaCl) forms during dissolution of sodium tetraborate-decahydrate (Na2B4O7.10H2O) in hydrochloric acid (HCl). The study presents that BMED process provides H3BO3 purification in dilute during the desalination process. In this study, desalination ratio, H3BO3 purification efficiency, acid and base production, specific energy consumption, and current efficiency were defined as performance indicators. The effects of initial H3BO3 concentration and flow rates of solutions on performance indicators were investigated under acidic condition. Additionally, two acidic conditions were evaluated with respect to desalination ratio and H3BO3 concentration in dilute. The results of the experiments indicated that the presence of H3BO3 does not affect the desalination process. The more H3BO3 concentration allows the more decrease in purification efficiency and current efficiency based on proton ions. The varying feed flow rate was found not effective on desalination, while purification efficiency increased with increasing flow rate. Initial H3BO3 concentration was determined as less effective on acid and base conversion than that of flow rate. In addition to simultaneous salt removal, acid and base recovery, the most important output of BMED will be H3BO3 recovery in high purity.

Evaluation of bipolar membrane electrodialysis for desalination of simulated salicylic acid wastewater

Salicylic acid (SA) is an important chemical raw material, but its production process generates large amounts of phenol-containing hypersaline wastewater. Bipolar membrane electrodialysis (BMED) technology was proposed to remove Na2SO4 from this wastewater and generate NaOH and H2SO4. The influences of initial pH in feed solution, current density, flow velocity, initial Na2SO4 concentration and volume ratio on the BMED process were investigated. These findings revealed that pH had no significant effect on the desalination rate, but affected the migration of organics including phenol and SA. When the input current density was 40 mA/cm2, flow velocity was 4.0 cm/s and the volume ratio was 2:1, the concentrations of H2SO4 and NaOH could reach the maximum at 0.97 mol/L and 1.56 mol/L respectively, with initial Na2SO4 concentration of 80 g/L and corresponding to a desalination rate of 96.3%. The current efficiency of acid was 55.2% and that of base was 50.2%, and energy consumption was 2.89 kWh/kg H2SO4 and 3.98 kWh/kg NaOH. These results confirmed BMED technology could treat simulated SA wastewater effectively and produce H2SO4 and NaOH. It provides a theoretical basis and guidance for the practical treatment of this type of wastewater.

Recovery of N, N-dimethylglycine (DMG) from dimethylglycine hydrochloride by bipolar membrane electrodialysis

A Bipolar membrane electrodialysis (BMED) was performed to achieve efficient production of N, N-dimethylglycine (DMG) from dimethylglycine hydrochloride. And the two-compartment cell configuration (BP-A) was used to avoid the amino acid macromolecules migrating through the membrane resulting in membrane fouling. Several experiment parameters including current density, initial dimethylglycine hydrochloride concentration and flow rate were discussed and compared. The results indicated that the optimal operation condition was at the current density of 50 A/m2, feed mole concentration of 0.3M and flow rate of 15L/h. Under the optimal condition, the energy consumption was 0.45 kWh/kg, the current efficiency was 65% and the recovery ratio for DMG reached 98% by calculation. In addition, the membrane fouling after experiments was conducted and further analyzed. It was observed that there was no appreciable change on the membrane during the BMED process by the SEM images and FTIR spectra. These results show that the harm of BMED process to membranes could be ignored. BMED method has the advantages of high purity, no by-products, low energy consumption and environmental friendliness. And this study can broaden the application of electrodialysis in the purification and preparation of macromolecular amino acids.