Bipolar Membrane Electrodialysis System Research Articles

Thermal effect of the stack in a bipolar membrane electrodialysis: Mechanism, risk, size effect and salt effect

Thermal effect inevitably occurred in a bipolar membrane electrodialysis (BMED) stack impacts its energy efficiency and potentially damages non-metallic components. Up to now, thermal mechanism and impacts within a BMED stack remain incompletely understood. Thus, thermal mechanism and impacts within the stack were investigated using the validated equivalent circuit model of a BMED system. Its results revealed that currents/Joule effect in the main circuit were dominant compared to those in the external circuit. The proportion of Joule heat in the main circuit exceeds 99.00 %, while that in the external circuit was less than 1.00 %. Joule heat generated in the outermost slot of the maximum conductivity compartment was obvious, while that in any position of the main circuit within the minimum conductivity compartment was also significant. Thermal impacts of non-metallic components were affected by the heat transfer of solution thermal effect. Besides, these effects which included current distribution, Joule effect, and thermal risk, were mainly affected by the size of the element at spacer, and the conductance provided by the salt and its products. Larger size of slots/ducts at spacer reduced the heat transfer efficiency at their location, while that of main channel enhanced the heat transfer efficiency between membranes and solution. Low conductivity salts and corresponding products pose a greater thermal risk for BMED stack. Meanwhile, these effects would be aggravated from the lab- to large-scale BMED stack. These findings can enhance the comprehension of the involved processes for optimizing BMED technique, thereby accelerating its development.

A sustainable bioprocessing system leveraging gas fermentation and bipolar membrane electrodialysis system for direct recovery of acetic acid

This study examined the integration of gas fermentation with bipolar membrane electrodialysis (BPMED) for sustainable production of acetic acid and bases, focusing on medium recycling and ion-exchange membrane optimisation. Gas fermentation was performed using an acetogenic microbe, Eubacterium callanderi KIST612, in a custom-designed gas bioreactor. The BPMED system was operated under specific voltage conditions to evaluate the proton and hydroxyl ion generation, ion concentration, and residual ratios. Gas fermentation consistently generated acetate with a stable CO2 consumption rate (0.167 mmol gcell−1) and an increased rate of conversion of carbon into biochemicals via methanol. The BPMED system efficiently produced acetic acid (acetate extraction rate of 99.72 %–99.82 %) and hydroxide ions (from 8 to 18 V), with operational challenges identified at higher voltage levels (≥20 V). The BPMED process, which includes additional membranes and exhibits a lower acetate flux than the ED process, had remarkable cost-effectiveness, surpassing the ED integration process by 17.6 %. This economic advantage was paralleled by a significant environmental benefit, where the BPMED process reduced carbon dioxide emissions by 7.4 % compared with the ED process. These results suggest that integrating gas fermentation with BPMED is a viable and sustainable approach for acetic acid production.

Bipolar membrane electrodialysis for nutrient recovery from anaerobic digestion dewatering sidestream

Anaerobic digestion (AD) offers an efficient means for treating sludge generated in wastewater treatment plants (WWTPs), but nutrient-rich AD dewatering sidestream contributes as much as 30 % of the overall nutrient loading of WWTPs. Several electrochemical approaches are being developed as a sidestream treatment strategy to prevent return of nutrients to WWTP headworks and recover them for fertilizer production. One such method is to produce acids and bases, essential chemicals necessary to facilitate nutrient recovery, using bipolar membrane electrodialysis (BMED). In this study we show simultaneous separation of nutrients and production of acid/base streams with an additional consideration for increasing the concentration of ammonium and phosphate in the final product stream by systematically altering compartment flow rates and hence the retention time of each stream. Using a three-compartment BMED system with a synthetic sidestream containing 50 mM NH3-N and 2 mM PO4-P, we achieved up to 80 % ammonia removal (via a cation exchange membrane) and up to 60 % phosphate removal (via an anion exchange membrane) at a productivity of 34.2 L m−2 h−1. Separated ammonia was recovered (>90 %) in a subsequent membrane contactor (MC) that was fed with acid and base streams produced by the BMED unit. A phosphate recovery > 80 % was achieved by chemical precipitation (CP). In a combined BMED-MC-CP process, the concentrated final product contained 333.9 mM NH3-N and 3.1 mM PO4-P with an energy consumption of 8.9 kWh kg−1 N recovered. These results illustrate that the BMED-based treatment train is a promising strategy for nutrient recovery from AD dewatering sidestream.

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.

Recovery of copper from electroplating sludge using integrated bipolar membrane electrodialysis and electrodeposition

Electroplating sludge, though a hazardous waste, is a valuable resource as it contains a large amount of precious metals. In this study, copper was recovered from the electroplating sludge using a technology that integrates bipolar membrane electrodialysis (BMED) and electrodeposition. The experimental results showed that Cu2+ in the electroplating sludge was successfully separated and concentrated in the BMED system without adding any chemical reagents; the concentrated Cu2+ was recovered in the form of copper foil in an electrodeposition system. Current density clearly affected the Cu2+ separation and concentration in the BMED system; the current density, solution pH and Cu2+ concentration drastically affected the Cu2+ electrodeposition ratio and the morphology and purity of the obtained copper foil. Under the optimised experimental conditions, 96.4% of Cu2+ was removed from the electroplating sludge and 65.4% of Cu2+ was recovered in the foil form. On increasing the number of electroplating sludge compartments from one to two and three, the current efficiency for recovering Cu2+ increased from 17.4% to 28.5% and 35.2%, respectively, and the specific energy consumption decreased from 11.3 to 6.7 and 5.3 kW h/kg of copper, respectively. The purity of the copper foil was higher than 99.5%. Thus, the integrated technology can be regarded as an effective method for recovering copper from electroplating sludge.

Nickel recovery from electroplating sludge via bipolar membrane electrodialysis

In this study, nickel (Ni) was recovered from electroplating sludge in the form of Ni(OH)2 using a bipolar membrane electrodialysis (BMED) system. The results showed that the H+ generated by the bipolar membrane could effectively desorb Ni from the sludge to the solution and the solution pH considerably affected Ni desorption. The desorption process can be described using the first-order kinetic model. The current density and solid/liquid ratio (m/v) considerably affected Ni recovery. Moreover, 100% of Ni was removed from the electroplating sludge and 93.5% of Ni was recovered after 28 h under a current density of 20 mA/cm2, a solid/liquid ratio of 1.0:15 and an electroplating-sludge particle size of 100 mesh. As the number of electroplating compartments increased from one to two and three, the current efficiency for recovering Ni changed from 12.1% to 11.8% and 11.9%, respectively, and the specific energy consumption decreased from 0.064 to 0.048 and 0.039 kW·h/g, respectively. Fourier-transform infrared spectroscopy and Raman spectroscopy showed that the precipitate obtained in this study is similar to commercial Ni(OH)2 and the purity of Ni(OH)2 in the obtained precipitate was 79%. Thus, the results showed that the BMED system is effective for recovering Ni from electroplating sludge.

Recovery of nickel, phosphorus and nitrogen from electroless nickel-plating wastewater using bipolar membrane electrodialysis

Electroless nickel-plating (ENP) wastewater is challenging to treat because of its complex composition. This study used bipolar membrane electrodialysis (BMED) to remove and recover Ni2+, NH4+, total phosphorus (TP) and NO3− from ENP wastewater. The results show that current density significantly affects ion removal and recovery, current efficiency, specific energy consumption and ion migration velocity. When the current density was 20 mA/cm2, the removal ratios of Ni2+, NH4+, TP and NO3− were 100%, 98.6%, 99.3% and 100% after 14 h, respectively, and their recovery ratios were 92.6%, 75.5%, 94.5% and 90.6%, respectively. The removal kinetics analysis showed that the removal of Ni2+, NH4+, TP and NO3− was consistent with the zero-order kinetics process. The current efficiency variated from 42.5% to 39.0% and 37.7%, and the specific energy consumption decreased from 1.67 to 1.38 and 1.32 kW h/mol with the equipped wastewater compartments increased from one to two and three in a BMED system. Post treatment, Ni2+ was recovered as Ni(OH)2, with a purity of 82.6% (commercial Ni(OH)2 purity = 90%). TP was recovered as struvite with a purity of 95.3%, and the physicochemical properties of the obtained struvite were similar to commercial struvite. NH4+ was recovered as (NH4)2SO4 and NH3•H2O. Therefore, BMED is an effective method to recover Ni2+, TP and NH4+ from ENP wastewater.

Separation and Concentration of Nitrogen and Phosphorus in a Bipolar Membrane Electrodialysis System.

Struvite crystallization is a successful technique for simultaneously recovering PO43- and NH4+ from wastewater. However, recovering PO43- and NH4+ from low-concentration solutions is challenging. In this study, PO43-, NH4+, and NO3- were separated and concentrated from wastewater using bipolar membrane electrodialysis, PO43- and NH4+ can then be recovered as struvite. The separation and concentration of PO43- and NH4+ are clearly impacted by current density, according to experimental findings. The extent of separation and migration rate increased with increasing current density. The chemical oxygen demand of the feedwater has no discernible impact on the separation and recovery of ions. The migration of PO43-, NH4+, and NO3- fits zero-order migration kinetics. The concentrated concentration of NH4+ and PO43- reached 805 mg/L and 339 mg/L, respectively, which demonstrates that BMED is capable of effectively concentrating and separating PO43- and NH4+. Therefore, BMED can be considered as a pretreatment method for recovering PO43- and NH4+ in the form of struvite from wastewater.

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.

Recovery of nickel in the form of Ni(OH)2 from plating wastewater containing Ni-EDTA using bipolar membrane electrodialysis

Ni is often present in plating wastewater as a complexing state. It is difficult to remove this Ni using traditional chemical precipitation technology. In this study, a bipolar membrane electrodialysis system was used to recover Ni in the form of Ni(OH)2 from plating wastewater containing Ni–ethylenediaminetetraacetic acid (Ni-EDTA) without adding chemical reagents. The stable structure of Ni-EDTA can be destroyed by H+ produced by the bipolar membrane to obtain free Ni2+, which can combine with OH− produced by the bipolar membrane to form Ni(OH)2. When the electrolyte Na2SO4 concentration, current density and initial Ni-EDTA concentration were 0.2 mol/L, 16 mA/cm2 and 1000 mg/L, respectively, 99.0% of Ni-EDTA was removed after 32 h. When the system was used to treat actual plating wastewater, 92.1% of Ni-EDTA was removed and 88.7% was recovered. When the number of wastewater compartments in the system was increased from one to three, the current efficiency increased from 1.7% to 5.8%, and the specific energy consumption decreased from 0.39 to 0.19 kW h/g. The results of an X-ray diffraction study indicate that the Ni(OH)2 obtained in this study is similar to commercial Ni(OH)2. Moreover, the recovery mechanism of Ni-EDTA was analysed. Thus, bipolar membrane electrodialysis can be regarded as an effective method to recover Ni from wastewater containing Ni-EDTA.

Retrieval of trivalent chromium by converting it to its dichromate state from soil using a bipolar membrane electrodialysis system combined with H2O2 oxidation

When a bipolar membrane electrodialysis (BMED) system is used to remove Cr(III) from the soil, the existing metal cations easily affect this removal owing to the migration competition of metal cations. To address this problem, herein, a BMED system combined with H2O2 oxidation was used to recover Cr(III) from soil in the form of Na2CrO4. The experimental results show that H2O2 can oxidise Cr(III) to Cr(VI), which can be recovered as Na2CrO4. The concentrations of electrolyte and humic acid in soil, current densities and addition time of H2O2 influenced Cr(III) recovery, current efficiency and specific energy consumption. Under optimal experimental conditions of a current density of 2 mA/cm2 and H2O2 addition time of 2 h after the BMED system was powered on, more than 69 % of Cr(III) could be recovered. When the number of equipped soil compartments increased from one to two and then to three, the current efficiency increased from 9.9 % to 19.8 % and then to 29.1 % and the specific energy consumption of chromium removal decreased from 7.04 × 10−2 to 5.51 × 10−2 and then to 4.72 × 10−2 kW∙h/g, respectively. When the BMED system was used to recover Cr(III) from actual soil, the recovery rate decreased to 55.9 % owing to the low Cr(III) oxidation rate resulting from more residual state Cr(III) being present in actual soil. Following treatment, the remaining Cr(VI) in soil can be reduced to Cr(III) by adding a reductant. Therefore, the BMED system combined with H2O2 oxidation can be regarded as an effective method for recovering Cr(III) from soil.

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.

Arsenic and cation metal removal from copper slag using a bipolar membrane electrodialysis system

A three-step bipolar membrane electrodialysis (BMED) system was used to remove arsenic and cation metals from copper slag (CS) generated during the copper ore hydrometallurgical process. The desorption kinetics results show that pH significantly influences metal desorption from CS. The Elovich model can be used to describe metal desorption. A high current density increased the metal desorption from CS into the supernatant. Metal removal also increased with current density when the BMED system was used for supernatant treatment. Increasing the number of supernatant compartments from one to two and three increased the current efficiency from 38.0% to 75.3% and 112.3%, respectively; the specific energy consumption decreased from 0.051 to 0.035 kWh/g and 0.029 kWh/g of metal removal, respectively. The supernatant (pH = 0.77) could be used as the leaching solution for leaching copper from raw copper ore during the copper ore hydrometallurgical process without discharging wastewater. During the treatment process, 79.6% of AsO43− could be recovered in the form of H3AsO4. The metal removal rates for arsenic, calcium, cadmium, cobalt, chromium, copper, iron, magnesium, nickel and zinc were 96.5%, 22.8%, 75.8%, 54.8%, 49.5%, 59.5%, 71.1%, 65.5%, 48.5% and 83.0%, respectively. Only a small amount of state-stabilised residual state metals remained in the CS, thereby realising the objective of recovering arsenic and removing cation metals. The present method was found to be an efficient and green technique for removing metals from CS and other solid waste materials contaminated with heavy metals.

Recovery of Cr(VI) and removal of cationic metals from chromium slag using a modified bipolar membrane system

A bipolar membrane electrodialysis (BMED) system equipped with a ‘back-to-back’ chromium slag compartment was fabricated to simultaneously recover hexavalent chromium (Cr(VI)) as Na2CrO4 and remove trivalent chromium (Cr(III)), Fe3+, Mg2+ and Ca2+ from chromium slag. Desorption experiments showed that the solution pH had a significant effect on the heavy-metal desorption efficiency from chromium slag. The BMED system can effectively recover more than 70.6% of Cr(VI) and simultaneously remove more than 99.9% of Fe3+, 87.8% of Mg2+, 26.2% of Ca2+ and 23.1% of Cr(III). When the number of ‘back-to-back’ chromium slag compartment modules was increased from one to two and three, the current efficiency increased from 11.2% to 17.2% and to 39.1%, respectively, while the amount of recovered heavy metals increased by factors of two and three, respectively. An analysis of the binding states showed that different chromium states were interchanging, which is beneficial to the Cr(VI) recovery and the Cr(III) removal. The experimental results indicated that the BMED system is as an effective technique for the simultaneous recovery of Cr(VI) and removal of Cr(III) from chromium slag and other types of solid waste contaminated with heavy metals.

Bipolar membrane electrodialysis for mixed salt water treatment: Evaluation of parameters on process performance

In the present study, bipolar membrane electrodialysis (BMED) process was employed as an alternative separation method to the distillation unit in the Solvay process for the synthetic soda ash production. The applicability of BMED was investigated by evaluating the effects of system parameters on process performance. Desalination ratio, salt based acid and base conversion ratio, flux, product purity, and energy consumption were defined as the process performance criteria for the BMED systems. Initial salt concentration, applied current and voltage, and initial acid and base concentrations were chosen as system parameters. The results of the study revealed that current/voltage and initial salt concentration are the most effective factors affecting all performance criteria. When all system parameters were considered, BMED provides the desalination ratio in between 90% and 98%, the acid and base conversion ratio of salt in between 60% and 80%, and the energy consumption in the range of 1.54–2.33 kWh/kg acid. Furthermore, the desalinated water can be reused as process water and the distillation unit waste problem can be resolved by the utilization of BMED system.

The effect of ion exchange membranes on the bipolar membrane electrodialysis of ammonium chloride wastewater

The different bipolar membranes and their configurations with monopolar ion exchange membranes from different manufacturers such as FAB-FBM-FKB, AHA-(BP-1E)- CMB, and JAM-(BMP-1)-JCM are used in the bipolar membrane electrodialysis (BMED) of simulated NH4Cl wastewater to examine the effect of membrane properties on the generation of HCl and NH3∙H2O. The results indicated that the configuration of AHA-(BP-1E)-CMB presented the promising performance among all the ion exchange membranes according to the generated acid and base concentration. And the configuration of FAB-FBM-FKB presented the expected performance on the membrane stack voltage, energy consumption, current efficiency of the BMED system. The stability of different ion exchange membranes in strong acid and base solution were investigated further by the analyses of SEM, contact angle and membrane resistance. It was found that the membranes AHA and FKB had better chemical stability than other membranes.

Simultaneous Removal of Trivalent Chromium and Hexavalent Chromium from Soil Using a Modified Bipolar Membrane Electrodialysis System.

In this study, a modified bipolar membrane electrodialysis system equipped with a "back-to-back" soil compartment was fabricated for simultaneous removal of trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)) from contaminated soils. The results showed that the soil solution pH had a significant effect on the Cr(III) and Cr(VI) desorption, and the desorption data fit well with the Elovich kinetic model. Current density had an obvious effect on Cr(III) and Cr(VI) removal, cell voltage, soil pH, current efficiency, and specific energy consumption, and the optimal current density was 2.0 mA/cm2. The removal efficiencies of Cr(III) and Cr(VI) were both 99.8%, while Cr(III) and Cr(VI) recoveries were somewhat lower at 87 and 90%, respectively, because some Cr(III) and Cr(VI) were adsorbed by the membranes. An energy consumption analysis indicates that the back-to-back soil compartment equipped system increased the current efficiency and decreased the specific energy consumption. When a system equipped with two back-to-back soil compartments was used to remove chromium from soil, the current efficiency increased to 28.8% and the specific energy consumption decreased to 0.048 kWh/g. The experimental results indicate that the proposed process has the potential to be an effective technique for the treatment of soil contaminated with heavy metals.

Cr(III) recovery in form of Na2CrO4 from aqueous solution using improved bipolar membrane electrodialysis

During the process of Cr(III) recovery from an aqueous solution using an electrodialysis or a bipolar membrane electrodialysis (BMED) system, the purity and recovery are often low because of the migration of co-existing cation ions, such as Na+, K+, Ca2+, and Mg2+. In this study, a modified BMED system was used to recycle Cr(III) from an aqueous solution in the form of Na2CrO4, which is a basic compound in the chromate chemical industry, after Cr(III) was oxidized to Cr(VI) by H2O2 under alkaline conditions. The electrolyte concentration in the Cr(III) solution and the current density influenced the chromium recovery, current efficiency, and specific energy consumption. Under optimal experimental parameters, i.e., 5.0 g/L Na2SO4 in Cr(III) solution and a current density of 0.5 mA/cm2, more than Cr(III) of 87.8% could be recycled. When the number of recovery chamber modules increased from one to two and then three, the current efficiency increased from 23.2% to 45.6% and 67.6%, and the specific energy consumption decreased from 1.19 to 0.89 and 0.73 kW∙h/g of chromium. The present technology was therefore found effective for recovering Cr(III) from aqueous solutions.

Fractional Factorial Design Application for the Determination of Affecting Parameters on the Generation of KOH and HCl From Simulated Wastewater Solution By Bipolar Membrane Electrodialysis Abstract

The aim of the study is to determine the significant factors influencing the generation of potassium hydroxide and hydrochloric acid from simulated potassium chloride solution by bipolar membrane electrodialysis using fractional factorial design. The membrane stack with acid, dilute (salt), and base compartments was used in the experiments. Fractional factorial design 24-1 was employed to evaluate the parameters affecting the production of base and acid. The process has been investigated as a function of four main factors namely, initial concentrations of acid and base, initial salt concentration, current density, and electrolyte concentration. Normal probability plot and Pareto charts revealed that the initial salt concentration is the most significant parameter affecting the bipolar membrane electrodialysis system performance. The results were also statistically analyzed by using the main effects plots and the ANOVA method. The significance of initial salt concentration was confirmed by both statistical findings.

Leakage circuit characteristics of a bipolar membrane electrodialyzer with 5 BP-A-C units

Leakage currents inevitably exist in all liquid channels of the plate-and-frame membrane stacks in bipolar membrane electrodialysis (BMED) systems. These leakage currents decrease the efficiency of the devices, and may even cause undesirable heat that can affect non-metallic components used in the membrane stack. In this study, a laboratory-scale BMED system was set up for treating high ammonium chloride organic wastewater. An electrical circuit model consisting of three hydraulic circuits in the membrane stack was established, and processed by using the simulation software Multisim. The leakage circuit characteristics of the BMED system with 5 BP-A-C units were monitored during the desalination process. The electrical resistances of the ducts/slots were shown to be influenced by solution conductivity and geometry. The voltages, currents, and thermal effects at the ducts/slots presented a symmetrical distribution in the membrane stack, and were affected by their electrical resistances during the desalination process. Measures were proposed to minimize any negative effects to improve the BMED design.