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Bipolar Membrane Electrodialysis for Nutrients Separation and Recovery from Wastewater

Submitted:

11 September 2026

Posted:

14 September 2026

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Abstract
Bipolar membrane electrodialysis (BMED) is an electro-membrane separation technology used for over 20 years to treat liquid wastes, including wastewater from various industrial processes, municipal wastewater, and animal farms. This technology has been developed for its ability to dissociate H2O into H+ and OH− ions and to convert cations and anions in the feed solution into bases and acids, respectively, by applying an electrical potential. In comparison with alternative treatment technologies, BMED has some advantages, such as no need for chemical reagents, high degrees of efficiency, and straightforward operational procedures. However, BMED has been limited by a high level of preparation expense for BMs, membrane deposition, and ion loss during operation. This review mainly describes the principles and designs of BMED, their compositions along with their advantages and disadvantages, the membrane fouling and cleaning, and also the trend of their application in wastewater treatment. Finally, the results on nutrient recovery by BMED show that the performance of BMED depends on the nature of the ion exchange membranes used, the composition of the sample solution, the process conditions, and the configuration of the membrane stack.
Keywords: 
bipolar membrane
;  
electrodialysis
;  
membrane fouling
;  
nutrients
;  
wastewater
Subject: 
Environmental and Earth Sciences  -   Sustainable Science and Technology

1. Introduction

In recent years, electro-membrane technologies have become more interesting in the field of environmental protection [1]. Among them, bipolar membrane electrodialysis (BMED) is a process in which, under an electrical potential, a selective separation of ions (cations and anions) and their recoveries in the form of base and acid without adding any chemicals is achieved through the use of cation-exchange membranes (CEMs), anion-exchange membranes (AEMs) and bipolar membranes (BMs) [2,3,4]. The method described above is a water treatment technology that can save the health of the environment by avoiding its contamination. It can be applied to the treatment of municipal wastewater, wastewater from industry, brackish water, in drug and food industries, chemical processes, heavy metals removal due to its ability to separate and recover ionic compounds in acidic and alkaline solutions from salt solution under the effect of electrical potential [3,5,6].
Due to the increasing amount of nitrogen and phosphorous in wastewater, some researchers have made efforts to recover these nutrient elements from waste liquids. According to Chirag et al. [7], nutrients extraction from wastewater can occur via different technologies such as chemical precipitation or crystallization, by gas-permeable membranes, and liquid–gas stripping. These treatment technologies use different chemicals for the pre- and post-treatment of water, which have a substantial negative impact on the environment, while the BMED process produces both concentrated and dilute streams without adding chemicals [8,9]. Furthermore, BMED can be used to separate and recover phosphates and ammonium from liquid waste in their acidic and basic forms [10]; respectively. This technology can also accomplish a separation of monovalent ions against multivalent ions by using monovalent selective ion exchange membranes. Wu et al. [11] reported that BMED, which is an electro-membrane process, is an efficient method for separating and recovering both NH4+, PO43-, and NO3- from salty wastewater. Despite its demonstrated potential, the practical application of the BMED process remains constrained by high operational costs, membrane fouling, ion losses, and limited understanding of how membrane properties, operating conditions, and stack configuration influence its nutrient recovery performance.
The aim of this review is to describe the principle of the BMED process, its advantages and disadvantages, the membrane fouling and cleaning, along with their applications in wastewater treatment.

2. Principles of BMED

The development of electro-membrane process has been limited by the higher H2 and O2 generation. In 1956, Frilette [12] proposed the bipolar membrane (BPM), which has low energy consumption [13]. During BMED, there is H2 and O2 generation, and there is no effect on the electrode. Additionally, the amount of energy consumed by BMED for 1 mol of water is 79.9 KJ/mol, while that of ED is 198.5 KJ/mol [4]. When compared to other electrochemical processes, these characteristics offer BMED greater application opportunities [2,4]. BMED is a membrane process distinguished by the application of BPM between electrodes [4]. This process is a rather new electro-membrane technique that uses an applied voltage to dissociate water into protons (H+) and hydroxide ions (OH−) [3,14]. This innovative technique features three fundamental configurations (two-chamber BMED containing base or acid; three-chamber BMED) per one cell pair according to its application and three types of ion exchange membranes (BM, CEM, and AEM) in specific arrangements [15]. Each unit of the three-chamber BMED has CEM, AEM, and BPM and can be beneficial for the separation and recovery of salts as acids and base [16].
Compared with other electrochemical process, BMED consumes low energy and has high economic effectiveness [4]. The voltage (0.828 V) needed for water dissociation in BPMs is significantly less than that of water electrolysis on electrodes (2.057 V) [17]. The following reactions show the potentials required on electrodes and in BPMs comparatively.
3H2O → 1/2O2 + H2 + 2H+ + 2OH−, 2.057 V
Cathodic reaction: 2H2O + 2e → H2 + 2OH−, 0.828 V
Anodic reaction: 2H2O → O2 + 4H+ + 4e, 1.229 V
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The low energy consumption of BMED helps to save power and the necessity of cooling. Another advantage of bipolar membrane water splitting is the absence of gas production, such as H2, O2, and Cl2, during water dissociation. Consequently, neither the cathode nor the anode is corroded [17].

2.1. BPMs

In the past decade, BPMs have been one of the various kinds of ion exchange membranes (IEMs) that have drawn more attention. These membranes consist of two layers: an anion exchange layer (AEL) and a negatively charged cation exchange layer (CEL), as well as an interface between the two layers known as the "bipolar junction" or "hydrophilic interface layer" (IL) [16,18]. In contrast to IEMs used for the separation of ions, BPMs are made to split water into hydroxyl and hydrogen ions at the bipolar intersection after an electrical current is applied. With the electrical current application, hydrogen and hydroxyl ions are produced by water electro-dissociation at the intermediate layer of the BPMs and move toward the cathode and anode compartments through CEL and AEL, respectively [19]. The arrangement of BPMs to the electrodes depends on the target: to ensure the water splitting into OH- and H+, the CEL must be positioned towards the cathode and the AEL towards the anode. This arrangement is a so-called “reverse-bias” condition. In fact, the protons (H+) pass through CEL, while OH- ions flow through AEL, creating an acid and a base on the membrane's opposing sides (Figure 2a). If the electrical field's orientation across the BPM is inverted, the CEL will then face to the anode and the AEL to the cathode. This position is called the “forward bias” condition (Figure 2b). Therefore, H+ and OH- ions move out of the external solutions towards the hydrophilic interface layer to form water from the acid-base neutralization reaction. Figure 2 shows the principle of BPM under reverse-bias and forward-bias modes.
In BPM, two reactions of protonation and deprotonation can be used to explain the mechanism of water dissociation [16,20].
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CH+ : fixed charged groups of AEL), K1;2: forward rate constants and K-1; -2: backward rate constants.
For the weak acid (AH), the reactions are
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These protonation-deprotonation reactions of water splitting can be summarized by the following equation:
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2.1.1. Cation Exchange Layer (CEL)

The positive type material of the cation exchange layer (CEL) is created by introducing an acceptor impurity, such as boron to silicon, which results in a shortage of valence electrons, or "holes”[16]. Due to this propriety, CEL allows only H+ to migrate toward the cathode. Different acids usually used in CEL are the groups of sulfonic acid and phosphoric acid groups in rare cases [19]. There are also other CEL based on poly (2,6-dimethyl1,4-phenylene oxide) as the organic component and (3-aminopropyl) triethoxysilane as the modified chitosan [20], inorganic hybridizing agent [21], polyetherketone [22] and sodium alginate [23]. Table 1 shows the types of polymers and ion exchange groups given in literature.

2.1.2. Anion Exchange Layer (AEL)

Quaternary ammonium groups on a polystyrene matrix are present in the majority of AELs of commercial BPMs [16]. Tertiary and secondary amines as well as various diamines are examples anionic groups. Table 2 shows different types of anion exchange membrane reported in literature [15].

2.2. Ion-Exchange Membranes

Ion-exchange membranes are made of semi-permeable polymers with functional groups added to the polymer matrix to impart either positive or negative charges. According to the membrane fixed functional group, membranes for cations exchange (negatively charged functional groups) and membranes for anions exchange (positively charged functional groups) are two different forms of ions exchange [24]. The mobile ions so-called counter-ions have an opposite charges of fixed group charges on the polymer. The mobile ions so called co-ions have the same charges with that of fixed groups [25]. Figure 1a and Figure 1b show migrations of cations and anions through cation exchange membrane and anion exchange membrane; respectively under an electrical field.

2.2.1. Mass Transfer

The components of mass transfer in the electromembrane process are IEMs, concentration polarization films, bulk solution and electrodes. According to Kabay et al. [26], ions transport within the membrane or electrolyte is controlled by migration, diffusion and convection. The derivative of the Nernst Planck equation with a convective term is frequently used to describe the ion flux in solution or the membrane at constant state [27]:
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Ji: ionic flux towards the membrane surface (mol/m2 s 1), Di: ion coefficient diffusion (m2 /s), zi and Ti: ion's transport and valence numbers, respectively, F: Faraday constant (C/mol), j: current density (A/m2), c: ion's molar concentration (mol/m3) and u: fluid velocity parallel to the membrane surface (m/s).

2.1.2. Membrane Fouling and Scaling

The most important factor that limits ions separation and recovery in BMED system is fouling and scaring phenomena. Wang et al. [28] and Lindstrand et al. [29] reported that membrane fouling is a significant issue that can impact the electro-membrane process by decreasing flux, raising membrane resistance, and consuming more energy. Membrane fouling is known as the deposition of insoluble biomass, colloids and organic components within the membrane or on its surface, such as oil, carbohydrates, proteins, aromatic substances and humic acid while scaling is the precipitation of salts present in feed solution on the surface or in the channels of membrane [14,30]. The main scaling ions are sulfate, bicarbonate, calcium, magnesium, and barium. Guo et al. [31] and Shirazi et al. [32] revealed that some organics (such as natural organic matter, protein, Surfactants, polysaccharides) and inorganics (such as Fe2O3, SiO2, Al2O3, CaPO4, CaCO3, CaSO4) are the most widely distributed organic and inorganic foulants and scales. It has been established that particles which are larger than the membrane's pore size are unable to pass through the membrane and lead to its deposition on the membrane's surface. According to Oztekin & Altin [33], as time progresses, the build-up of foulants and scales on the membrane surface increases, resulting in the formation of a gel layer. The gel layer undergoes an increase with an increase in charge accumulation, subsequently becoming both thinner and denser. Oztekin & Altin [33] also reported that fouling potential is increased by high concentrations of salts in feed solution. The previous studies regarding membrane accumulation have more interested on membranes for anion exchange. Most of research works carried out have shown that fouling affects AEMs more than CEMs because of the negatively charged colloids in natural water [34].
The foulants which can affect AEMs are organic compounds such as natural organic compounds whereas colloidal materials, proteins, insoluble inorganic salts affect CEMs [33]. High hydrodynamic pressure loss and flow deterioration during the process are attributed to the presence of suspended solids, silicates and substances exhibiting low solubility, including iron hydroxide and calcium carbonate. The electrical resistance is increased by precipitation of compounds on the membrane surface and lead to physical damage of membrane structure [35]. The precipitation of inorganic salts results in the formation of crystals on the membrane surface and this phenomenon is reversible [36]. Various compounds which lead to different precipitation effect during electro-membrane process are heavy metals, alkaline metals; dissolved gases, inorganic and organic colloidal substances, dissolved organic compounds and biomass [35].
Lindstrand and al. [29] investigated the influence of different organic solutes on the fouling phenomenon on membrane, and observed that the resistance of CEMs was marginally increased, while AEMs were fouled by all solutes tested. It was also reported that the observed difference was attributed to the electrostatic interactive relation existing between the negative charges of the membrane and the negatively charged organic molecules.
Current density is another parameter which affects the fouling of IEMs by making fast fouling at higher current densities [37]. In general, fouling phenomenon in ED systems relies on the chemical and physical characteristics of the foulants, the characteristics of membranes, and also the solution properties. They affect the performance of the membrane by flux drop or increase in the electrical resistance of the membranes

2.1.4. Prevention and Mitigation of Membrane Deposition

Many researches have been conducted on the reduction of membrane fouling and some methods proposed are the induction of turbulence in the cell compartments, the preliminary treatment of the feed solution, the improvement of process conditions and membrane properties [33]. Electro-membrane process is more resilient to membrane fouling resulting from suspended particles than RO, MF, UF and NF [38], because of frequent electrode reversal, also known as EDR which can decrease fouling build-up on membranes [39,40]. Chemical cleaning and EDR operation can be used to eliminate the inorganic fouling. According to Lin et al [39], EDR is an efficient process in prevention of membrane fouling by regularly changing the electrode polarities. While ions are being transported, the substances aggregate and chemicals precipitate on the membrane's surface coverage. AEMs are easily fouled by foulants that deposit on the membrane surface because so many of them have negative charges. The dissociation of the particles from the membrane surface using EDR, greatly reduces fouling brought on it by particles aggregation and chemical deposition. However, all foulants cannot be cleaned by EDR or chemicals. Some substances are partially cleaned off by acid solution, creating reversible EDR fouling, whereas some cannot be removed, creating irreversible EDR fouling [39].
The selection of chemical compound to be applied for the purpose of membrane cleaning is contingent upon the membrane's type, the intensity of the contamination and the nature of the pollutants present. The following chemicals are typically advised by membrane producers: weak and strong acid solutions, alkali solution (e.g. NaOH solution), cleaning agents (detergents), complexing agents (e.g. EDTA), disinfectants (e.g. H2O2, NaOCl) and enzymes [34]. Also operational conditions can be considered to reduce fouling. Additionally, Wang et al. [28] investigated the impacts of hydraulic cleaning, acid cleaning, and mixed methods with ultrasound for particles removal on IEMs. The combination of acid cleaning and ultrasound treatment is the most effective cleaning method, which removes the foulants from the surface and inner parts of CEMs [28]. Table 3 shows the kinds of foulants, their charge characteristics, fouling avoidance techniques, and/or cleaning procedures.

3. Applications of BMED Process

3.1.. Acid and Base Production from Liquid Waste by BMED
BMED process appears more attractive in wastewater treatment due to its ability to move ions of a salt solution and to convert them into base and acid (figure 3). Many previous studies investigated the acid and base recovery from wastewater. Gao et al. [41] examined the recovery of hydrochloric acid and sodium hydroxide from sodium chloride contained in wastewater using a BMED system. They indicated that the initial concentration of sodium hydroxide had little or no effect on the acid production, whereas the current density has a significant impact. BMED has also been used to product and recover organic acids including, citric acid [42], acetic acid [43], lactobionic acid [44], succinic acid [45], malic acid [46], tartaric acid [47], propionic acid [48], gluconic acid [49], vitamin C [50], amino acids [51], formic acid [52] and salicylic acid [53]. The flow sheet depicted in Figure 3 shows BMED process for acid and base recovery.
Chen et al. [54] suggested a novel technology called BPM selective electrodialysis (BMSED) to separate Na+/Ca2+ and Cl−/SO42− ions found in concentrated saline solution. This process consists of a monovalent AEM and a monovalent CEM which only permit monovalent ions to migrate through in order to produce a high purity acid/base. The results of this study shown that the purity of HCl and NaOH were both close to 99.9% [54]. Table 4 shows acid and base produced from different salt solutions and liquid waste using BMED.

3.2. Nutrients Separation and Recovery from Wastewater by BMED

The growing urban, rural and industrial water supply increase the amount of wastewater containing different contaminants and nutrients [2]. The management of this wastewater has become one of the environmental and economic challenges. The contamination of surface waters and groundwater by these nutrients is a serious problem around the world. Excessive amount of nitrogen and phosphorous in water causes methemoglobinemia in infants [26] and eutrophication [60]; respectively.

3.2.1. Nitrogen Separation and Recovery from Wastewater by BMED

BMED has been utilized frequently in recent years to separate and recover ammonia from aqueous waste. Li et al. [61] treated simulated NH4Cl of wastewater by BMED and recovered HCl and NH3 solutions. Their findings showed that the energy consumption remained constant at 19 MJ/kg of nitrogen, whereas the ammonia removal efficiency ranged from 85% to 91%. Zhang et al. [62] have investigated the effects of humic acid, Mg2+, and Ca2+ on the extraction of ammonium from a leachate and their findings showed a significant effect with more than 86% of ammonium removal. Gao et al. [60] recovered ~77% nitrogen by a hybrid electrochemical process that combines membrane capacitive deionization (CDI) and BMED. Wu et al. [11] used BMED with monovalent anion exchange membrane to separate and recover NH4 +, PO43−, NO3− from wastewater. They indicated that the separation rates of NH4+, PO43−, and NO3− increased with current density. At 1.0 mA/cm2, the separation rates of NH4+ and NO3− after 140 min were 100% and 100%, while their recoveries were 79.1% and 34.2%, respectively. They explained that this difference in the separation and the concentration rates is caused by membrane adsorption during the process.
Recently, Cao et al. [63] recovered 78.3% of Nitrogen (NH4 +) from simulated wastewater by using BMED. They also noted that the separation and recovery rates of NH4+ increases both with time and current density. By increasing of current density, the amount of energy consumed steadily rises. The separation and recovery rates of ammonium carried out using different type of BMED process depend on the characteristics of ion exchange membrane, sample solution, treatment conditions and the configuration of the stack. Table 5 shows different separation and recovery rates of nitrogen reported in literature.

3.2.2. Phosphorus Separation and Recovery from Wastewater by BMED

BMED has attracted increasing attention as a sustainable approach for nutrient recovery, particularly in the context of phosphorus scarcity and the development of circular economy strategies for wastewater management [4,11]. It has been demonstrated through experimental studies that BMED is capable of effectively separating and concentrating phosphate ions (PO43-) from dilute wastewater streams. This, in turn, has been shown to improve the feasibility of subsequent phosphorus recovery processes, such as struvite precipitation or phosphoric acid production [11]. Furthermore, BMED has been successfully applied to the recovery of phosphorus from various aqueous matrices, including synthetic wastewater and industrial by-products, thereby highlighting its versatility and resource recovery potential [67].
Characteristics such as ion-exchange capacity, membrane selectivity, electrical resistance, water dissociation efficiency, and chemical stability directly affect phosphate transport and energy requirements. The utilisation of high-selectivity membranes has been demonstrated to reduce the co-transport of competing ions and enhance phosphorus concentration in the recovery compartment [4].
Additionnally, the performance of BMED in terms of phosphorus recovery is strongly dependent on the stack configuration. The arrangement of BPMs, AEMs, and CEMs determines ion migration pathways and phosphorus selectivity. As demonstrated by Wu et al. [11], BMED configuration incorporating selective membrane compartments was found to be an effective means of separating phosphate from competing ions, such as nitrate. This process served to enhance phosphorus enrichment, thus facilitating its subsequent recovery as struvite. The authors observed phosphorus transport efficiencies above 80%, thus demonstrating that stack design plays a critical role in nutrient separation. Table 6 shows different separation and recovery rates of phosphorus, membrane properties, BMED configuration and sample used as reported in literature.
Consequently, phosphorus recovery by BMED is not governed by a single factor but rather by the combined effects of membrane-stack configuration, membrane characteristics and wastewater composition, and process operating conditions, all of which must be carefully optimized to achieve high separation efficiency, phosphorus purity, and recovery performance.

4. Conclusions

BMED have a high potential in valorization and desalination of wastewater for its applications to recover dilute water and valuable components. The advantages associated with this process include the following: An increase in the quality of the product; more environmentally friendly process and an increase in the longevity of ion exchange membranes. BMED also exhibits certain advantageous properties, including the absence of a requirement for chemical reagents, high efficiency and a straightforward operational process, which explains why it has been widely employed in the fields of environmental protection and resource recovery. The energy consumption of BMED lower than that of conventional ED. It is evident that these properties afford BMED superior application prospects in comparison to other electrochemical technologies. However, the BMED system has been shown to be limited by a high expense of preparation, membrane deposition and ion loss during operation. Membrane fouling, which is caused by the accumulation of particles and chemical deposition, can be significantly mitigated through a process of dissociation from the membrane surface. It has been demonstrated that pre-treatment of the feed solution and good operating conditions are effective methods for resolving the problem of membrane fouling during operation. The issue of ion leakage can be resolved through the implementation of an acid-blocking membrane, the regulation of cell voltage, current density, and salt compartment solution pH to prevent or diminish the migration of H+. Hence, the efficiency of BMED is influenced by various parameters, including the feed conditions, the properties of the membrane, the electrical current density, and the configuration of the stack structure. This process technology has been used for nutrients separation and recovery from aqueous waste. The separation and recovery rates of ammonium and phosphate carried out using different type of BMED processes depend on the characteristics of ion exchange membrane, feed sample solution characteristics, process conditions and the configuration of the stack.

Author Contributions

All authors: conceptualization, E.N and S. N: investigation, writing—original draft preparation; S.B. and N.K.: review, editing and supervision; S.B.: funding acquisition and project administration. All authors have read and agreed to the published version of the manuscript.

Funding

This study was supported by the European Union through the African Research Initiative for Scientific Excellence (ARISE) pilot program under Grant No. DCI-PANAF/2020/420-028. The European Commission and the African Union Commission assist the African Academy of Sciences in implementing ARISE. The authors of this publication are responsible for its content, which should never be interpreted as representing the position of the African Union Commission, the African Academy of Sciences, or the European Union.

Acknowledgments

The authors are thankful to the University of Burundi for providing all administrative and research facilities required to perform the preparation of this review.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.:

Abbreviations

AEMs Anion-Exchange Membranes
AEL Anion Exchange Layer
BMs Bipolar Membranes
BMED Bipolar Membrane Electrodialysis
BMED-MCDI Bipolar Membrane Electrodialysis and Membrane Capacitive Deionization
SBMED Selective Bipolar Membrane Eletrodialysis
CEMs Cation-Exchange Membranes
CEL Cation Exchange Layer
ED Electrodialysis
IEMs Ions Exchange Membranes
IL Interface Layer
MF Microfiltration
MEM monovalent exchange membrane
RO Reverse Osmosis
RED Reverse Electrodialysis
UF Ultrafiltration
ENP Electroless Nickel-Plating
MC Membrane Contractor
CP Chemical Precipitation
RO Reverse Osmosis
CD Capacitive Deionization

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Preprints 232851 g001
Figure 2. Principle of a BPM: (a) BPM under reverse bias, where water dissociates into H+ and OH-; (b) BPM under forward bias, where ions are transported into the membrane and to form water at the bipolar junction.
Figure 2. Principle of a BPM: (a) BPM under reverse bias, where water dissociates into H+ and OH-; (b) BPM under forward bias, where ions are transported into the membrane and to form water at the bipolar junction.
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Figure 1. (a) Migration of cations through the cation exchange membrane ; (b) Migration of anions through the anion exchange membrane.
Figure 1. (a) Migration of cations through the cation exchange membrane ; (b) Migration of anions through the anion exchange membrane.
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Preprints 232851 g003
Figure 3. Flow diagram of BMED for the recovery of acid and base from liquid waste.
Figure 3. Flow diagram of BMED for the recovery of acid and base from liquid waste.
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Table 1. CEL types of BPMs [15].
Table 1. CEL types of BPMs [15].
Polymer(s) Ion exchange group Remarks
Poly-styrene-co-divinylbenzene Sulfonic acid Heterogeneous (poly-vinylchloride binder)
Poly-styrene-co-divinylbenzene Phosphoric acid Poly-ethylene binder
Nafion Sulfonic acid Homogeneous
Grafted perfluorinated polymer membranes Sulfonic acid -
Poly-butadiene-co-styrene Sulfonic acid -
Poly-phenylene oxide or poly-styrene Sulfonic acid Homogeneous
Poly-ether sulfone Sulfonic acid Homogeneous
Poly-sulfone Sulfonic acid Homogeneous
Table 2. CEL types of BPMs.
Table 2. CEL types of BPMs.
Polymer(s) Ion exchange group Remarks
Poly-styrene-co-divinylbenzene Tertiary and quaternary amines Cross-linked resin, heterogeneous
Poly-sulfone Di-amines Cross-linked homogeneous
Poly-sulfone Quaternary amines Homogeneous
Poly-vinylidene fluoride blend with poly-vinyl benzyl chloride Different diamines Cross-linked
Poly-ether sulfone Quaternary amines Homogeneous
Poly-methyl methacylate-co-glycidyl methacrylate Quaternary amines -
Table 3. Foulants and cleaning methods of IEMs [33,34].
Table 3. Foulants and cleaning methods of IEMs [33,34].
Foulant type Definition Foulant formula Charge properties Cleaning methods
Scale precipitates formed by the solution's less soluble salts CaCO3, SrSO4, CaSO4.2H2O, SiO2, BaSO4 Non - Adjustment of pH levels,
- Utilization of citric acid or EDTA
Molecular colloids Stack of suspended material on membrane areas SiO2,Fe(OH)3, Al(OH)3, Cr(OH)3 Negative - Pretreatment with MF, UF, higher flow rate,
- Adjustment of pH levels,
Organics Adsorption of organic species to membrane surfaces Macromolecules, proteins, whey, polyelectrolytes, humate Negative -Pretreatment with MF, UF, activated carbon,
- Clean with NaOH
Table 4. Acid and base production from liquid waste and salt solutions by BMED.
Table 4. Acid and base production from liquid waste and salt solutions by BMED.
BMED system Wastewater type Membrane properties Acid production Base production References

BMED:
BM-AEM-CEM
Saline textile wastewater (Na2SO4)		 Characteristics BM AEM CEM
66.9 % of SO42- converted in H2SO4
72.2 of Na+ converted in NaOH
[55]
Thickness (μm) - 140 -160 180-210
Surface resistance (Ω/cm2) - 3.5 - 4.5 2.5-3.5
Transfer number - > 0.93 > 0.93
IEC (meq/g) - 0.5-0.6 0.8-1.0
BMED:
BM-AEM-CEM		 NH4Cl and NaCl Thickness (μm) 200-350 160-200 160-200 60 % of Cl- converted in HCl 80 % of NH4+ and Na+ converted in NH4OH and NaOH [56]
Surface resistance (Ω/cm2) - 2 2.5
Transfer number >0.95 > 0.95 > 0.95
Water splitting voltage (%) 0.8-1 - -
BMED:
BM-CEM-AEM		 RO brines Resistance Ω(cm2) - < 8 < 9 60-90% of HCl 60-90% of NaOH [57]
Transfer nº counter-ion - > 0.98 > 0.98
Water splitting efficiency (%) > 99 - -
Exchange capacity (mval/g) - 1.8 2.2
Burst strength (kg cm−2) 6 - -
RO-ED-BMED Cold-rolling wastewater Tickness (μm) 160-230 120-180 140-200 2.35 M H2SO4 2.03 M NaOH [58]
Ion-exchange capacity (meq g -1) - 1.5-1.8 1.5-1.8
Area resistance (Ω cm2) - 2.0-3.5 1.8-3.8
Permeaselectivity (%) - > 96 > 96
BMED:
BM-AEM-CEM		 Solid waste residue (CH3COONa) Thickness (mm) 0.18-0.20 0.11-0.15 0.13-0.15 87.7% of CH3COOH 99.0% of NaOH [59]
Burst strength (MPa) - 0.16 0.16
Area resistance (Ω cm2) < 3 1.5−3.0 2.5-3.0
Transport number (%) - >96 >96
Chemical stability (pH) 1-14 - -
Table 5. Separation and recovery of nitrogen from wastewater using BMED.
Table 5. Separation and recovery of nitrogen from wastewater using BMED.
System Wastewater type Membrane characteristics Nitrogen separation Rate ( %) Nitrogen recovery Rate (%) References

Proposed BMED
Simulated wastewater		 Characteristics BM AEM CEM 96.5 78.30 [63]
Thickness (mm) 0.16-0.23 0.12-0.20 0.16-0.23
Surface resistance (Ω/cm2) 2.0-2.8 1,5-2.0 1.8-2.4
Transfer number (%) 95-99 >98 90-95
IEC (meq/g) 2.0-2.8 1.5-2.0 1.8-2.4
SBMED Thickness (μm) 170-260 420 50.8 100 79.1 [11]
Exchange capacity (mol/kg) - 2.2 0.95-1.01
Synthetic wastewater Selective transmission coefficient (%) - 90 -
Water decomposition efficiency (%) >98 - -
Rupture strength (MPa) 0.4-0.7 0.6
Moisture content (%) - 42 5 ± 3.0

BMED-MCDI
Synthetic wastewater		 Membrane type Fumasep FBM Neosepta AMX Neosepta CMX
-		 77 [60]
Membrane area (cm2) 17.5 17.5 17.5
Thickness (mm) 0.5 0.5 0.5

BMED (five cells): BM-AEM-CEM
Leachate		 Thickness（μm） 180-220 90-100 140-150
86.17
72.55
[62]
IEC (meq/g) 0.8-1.0 0.8-1.0 0.8–1.0
Moisture content
（%）		 45-55 15-20 35-40
Surface resistance
（Ω·cm2）		 - 2.5-3.5 1.5-2.5
Number of migrations - >0.94 >0.98

BMED: BM-AEM-CEM
Simulated NH4Cl wastewater		 Thickness (μm） 0.24-0.26 0.24-0.26 0.3 - 63.6 [61]
IEC (meq/g) - 1.6-1.7 2±0.02
Water content
（%）		 - 20-24 35
Surface resistance
（Ω·cm2）		 8-9 7-10 ≤ 4.5
Number of migrations - ≥96 >98
Burst strength (×105Pa) 2.5-3.0 - -

BMED: 5 Cell pairs (BM-CEM) and end AEM
 Product of wastewater treatment plant Thickness (μm） 1.1 0.5 0.6 95 87 [64]
IEC (meq/g) - ≥ 2.4 ≥ 2.1
Surface resistance （Ω·cm2） - 7.0 10.0
Transport Number(%) - 82% 95%
Burst strength (kPa) > 2206.3 1034.2 1034.2
pH operation range 1-14 < 10 1-14

BMED: BM-CEM
 Dewatering centrate and low-grade sulfuric H2SO4
 Thickness (μm） 1.1 0.5 0.6 - 88.4 [65]
IEC (meq/g) - ≥ 2.4 ≥ 2.1
Surface resistance （Ω·cm2） - 7.0 10.0
Transport Number(%) - 82% 95%
Burst strength (kPa) > 2206.3 1034.2 1034.2
pH operation range 1-14 < 10 1-14
Two-stage BMED pig manure hydrolysate Thickness (mm) 0.4 < 0.45 < 0.45 - 86
 [66]
Swell difference (%) < 22 < 50 < 50
Area resistance (Ω·cm2) - < 8 < 8
Transport number (%) - > 95 > 95
Selectivity (%) > 90 > 90
Table 6. Separation and recovery of nitrogen from wastewater using BMED.
Table 6. Separation and recovery of nitrogen from wastewater using BMED.
BMED System Wastewater type Membrane properties Phosphorus separation rate (%) Phosphorus recovery Rate (%) Refere-nces

Tree-compartment-BMED: BM-AEM-CEM-BM

Synthetic wastewater imitating the liquid fraction of animal manure		 Characteristics BM AEM CEM - 96 [68]
Thickness (mm) < 0.50 < 0.70 < 0.70
Specific conductivity(mS/cm2) - 109.7 117.3
Water splitting voltage 1.20 - -
IEC (meq/g) 2.0-2.8 1.5-2.0 1.8-2.4
Two-stage BMED Pig manure hydrolysate Thickness (mm) 0.45 < 0.45 < 0.45 - 75 [66]
Swell difference (%) < 22 < 50 < 50
Area resistance (Ω·cm2) - < 8 < 8
Transport number of K+ (%) - > 95 > 95
Selectivity (%) > 90 > 90
Three-compartment BMED-MC-CP Synthetic AD dew atering sidestream comprising 50 mM NH4Cl, 50 mM NaCl, and NaH2PO4 (0.5–4.0 mM) Membrane type Fumasep FBM Fumasep FAS-PET-75 Fumasep FKB-PK-75 - > 80 [69]
Thickness (μm) 340 340 340
Membrane area (cm2) 29.2 29.2 29.2
BPMED-MCDI Synthetic wastewater Membrane type Fumasep FBM Neosepta AMX Neosepta CMX ~89 - [60]
Membrane area (cm2) 17.5 17.5 17.5
Thickness (mm) 0.5 0.5 0.5
BMED with ion exchange absorption T-52H Resin Synthetic solution of NaH2PO2 solution Membrane type Fumasep FBM Neosepta AHA Neosepta CMB - 80.06 [70]
IEC (mequiv·g−1) - 1.4-1.7 1.5-1.8
Area resistance (Ωcm2) <3.0 2.0-3.5 1.8-3.8
Thickness (mm) 0.20 0.12-0.18 0.14-0.20
Transport number (%) 98 95 97
BMED combined with RA Triethylammonium phosphate wastewater Effective area of the membrane (cm 2) 21 × 7 21 × 7 21 × 7 - 96 [71]
BMED:
BM-AEM-CEM		 Electroless nickel-plating (ENP) wastewater Effective membrane area (cm2) 12 12 12 99.3 94.5 [72]
BMED with magnesite tailings added to the TTC Simulated aquaculture wastewater containing NH4Cl, NaH2PO4 and NaCl Surface area (cm2) 37.5 37.5 37.5 - 97.9 [73]
Distance of between different membranes (cm) 5 5 5
BMED:
BM-AEM-CEM		 Synthetic solution (Na3PO4·12H2O, Na2HPO4· 12H2O and NaH2PO4·2H2O) Membrane type Neosepta BP-1 Neosepta AMX Neosepta CMX 95.8 80.3 [74]
Thickness (μm) 200-350 120-180 220-260
IEC (meq·g−1) - 1.4−1.7 1.5-1.8
Area resistance (Ω cm2) - 2.0−3.5 2.0-3.5
Voltage drop (V) 1.2-2.2 - -
efficiency (%) >98 - -
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