Investigation of the Anion Migration Mechanism in Microbial Desalination Cells: Interaction and Actual Operational Impact

Microbial desalination cells (MDCs) are an efficient method for the desalination of saline wastewater driven by the metabolism of bacteria via an organic oxidation mechanism. Systematic studies have been conducted to elucidate anion-dominated interactions to avoid unforeseen risks in microbial desalination cells during the long-term treatment of complex wastewater containing various anions. Despite different anion migration interactions having less effect on MDC operation compared with cations, they are influenced by their own properties (hydrated ion radius, diffusion coefficient and equivalent conductance) and the ambient solution. This also led to the removal efficiency of different anions in MDC in the following sequence: NO3− > Cl− > SO42−. The high Gibbs hydration energy of SO42− and the hydrophobicity of the anion exchange membrane affect the transmembrane migration of SO42−. However, the high steric hindrance formed on the membrane also inhibits reverse diffusion at the end of the cycle. In addition, the anodic biotopography and community caused by the migration of different anions change, such that the number of denitrifying bacteria increases and the relative abundance of electrogenic bacteria further improves. With decreasing anodic pH, electrogenic microorganisms form a shell to protect against anodic biogenesis. In this study, MDC was used to treat actual industrial tailwater, and the salt removal efficiency stabilized at 63.2–74.1%.