Flow condition mitigates the inhibition of high concentration Cu ²⁺ on the sulfate reduction performance of microbial electrolysis cell

Microbial electrolysis cells (MECs) are promising for treating acidic mine drainage (AMD) containing high concentrations of sulfates and heavy metals. However, the performance of MEC cathodic biofilms is influenced not only by high heavy metals concentrations but also by hydrodynamic mixing conditions. Yet, there is a lack of precise assessment on the impact of hydrodynamic mixing conditions on MEC treating sulfate-laden wastewater under high heavy metal stress, and the defense mechanisms of MECs remain unclear. This study investigated the effects of different hydrodynamic conditions (EG, flow condition; CG, stationary condition) on the performance of MECs treating sulfate wastewater under high heavy metal stress, delving into microbial activity, community composition, electrochemical performance, and microbial defense capabilities against heavy metals. The results indicated that under heavy metal stress, microbial cells underwent severe deformation and death, with the assimilatory sulfate reduction pathway severely impaired, leading to a decline in MEC performance, and the reduction rate of CG group was finally reduced to 14.47%. In contrast, under flow conditions, the EG group exhibited increased extracellular polymeric substances (EPS) composition, enhanced biofilm community diversity, and elevated levels of copper resistance genes, significantly mitigating the inhibitory effects of Cu²⁺ on microorganisms, ultimately maintaining a performance of 47.18%. Ultimately, Cu²⁺ in the system was removed through bioprecipitation and biosorption, forming CuS and Cu(OH)₂. This work provides critical insights for scaling up MEC technology to address co-contamination challenges in acid mine drainage remediation, particularly for environments with hydrodynamic mixing conditions and elevated heavy metal concentrations.