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.

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.