Samuel Bunani

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.

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.

Rising concentrations of organic carbon (OC), phosphorus, and nitrogen in liquid waste from urban, industrial, and agricultural sources pose persistent challenges for environmental protection and resource recovery. Despite extensive application of microfiltration (MF) and ultrafiltration (UF) in wastewater treatment, their role in selective organic carbon and nutrient fractionation remains insufficiently clear-cut and is often interpreted solely through nominal pore size. This review was guided by the hypothesis that the reported limitations of MF and UF for nutrient separation are not intrinsic to the technologies but arise from simplified interpretations of separation mechanisms. A unified analytical framework was developed by synthesizing recent studies, linking membrane surface charge, pore structure, solute speciation, fouling-induced secondary layers, and operating conditions to the observed separation behavior. The analysis shows that MF fractionates particulate OC and suspended solids, whereas UF extends separation to macromolecular OC and phosphorus mainly via indirect retention mechanisms. Dissolved nitrogen species largely permeate both membranes unless they are transformed into retainable forms. Performance differences between MF and UF are conditional and system-dependent, with enhanced selectivity emerging through process integration. MF and UF can thus be repositioned as strategic fractionation interfaces within integrated treatment systems supporting circular economy–oriented wastewater management.

The increasing generation of liquid waste from agricultural, industrial, and municipal sources poses significant environmental challenges due to its high content of organic carbon (OC) and nutrients such as phosphorus and nitrogen. This review examined the effectiveness of membrane-based technologies, particularly microfiltration (MF) and ultrafiltration (UF), in separating and recovering these valuable compounds. Drawing on key literature indexed in Scopus, the review analyzed how membrane properties, operating conditions, and feed characteristics influence removal efficiency. The find-ings indicate that MF membranes primarily retain particulate organic matter and sus-pended solids (SS), with limited retention of phosphorus and nitrogen species. In con-trast, UF membranes exhibited superior performance in removing both OC and phos-phorus, and partially retain some nitrogen compounds depending on molecular size and charge. When combined with pre-treatment processes such as coagulation or ad-sorption, both MF and UF achieve higher nutrient removal rates. These membrane technologies showed promise not only in reducing pollutant loads but also in enabling nutrient recovery for potential reuse in agriculture. The optimization of membrane configuration and integration with other processes is essential for enhancing treatment performance and contributing to circular wastewater management strategies.

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.

Membrane bioreactor (MBR) effluent collected from a wastewater treatment plant installed at an industrial zone was used for reverse osmosis (RO) membrane tests in the laboratory. For this, two different GE Osmonics RO membranes (AK-BWRO and AD-SWRO) were employed. The results showed that AK-brackish water reverse osmosis (AK-BWRO) and AD-seawater reverse osmosis (AD-SWRO) membranes have almost similar rejection performances regarding analyzed parameters such as conductivity, salinity, color, chemical oxygen demand (COD), and total organic carbon (TOC). On the other hand, these membranes behaved quite differently considering their permeate water flux at the same applied pressure of 10 bar. AD-SWRO membrane was also tested at 20 bar. The results revealed that AD-SWRO membrane had almost the same rejections either at 10 or at 20 bar of applied pressure. Compared with irrigation water standards, AK-BWRO and AD-SWRO gave an effluent with low salinity value and sodium adsorption ratio (SAR) which makes it unsuitable for irrigation due to the infiltration problems risi0ng from unbalanced values of salinity and SAR. Combination of MBR effluent and RO effluent at respective proportions of 0.3:0.7 and 0.4:0.6 for AK-BWRO and AD-SWRO, respectively, are the optimum mixing ratios to overcome the infiltration hazard problem. Choice of less-sensitive crops to chloride and sodium ions is another strategy to overcome all hazards which may arise from above suggested mixing proportions.