Study on the effect and mechanism of Cu²⁺ stress on sulphate reduction in microbial electrolysis cells

Sulphate-rich industrial wastewater is often contaminated with heavy metals, yet their influence on microbial sulphate reduction remains poorly understood. This study investigated the response of sulphate-reducing bacteria (SRB) in a microbial electrolysis cell (0.8 V, 48 h cycles) to stepwise increasing Cu²⁺ concentrations (8-125 mg/L) under stirred conditions. When Cu²⁺ concentration increased from 8 to 55 mg/L, sulphate reduction efficiency over 48 h remained stable at approximately 90%, suggesting good SRB tolerance. When Cu²⁺ concentration was 85 mg/L, sulphate reduction efficiency over 48 h dropped sharply to 30-60%, coinciding with persistent Cu²⁺ removal below 40%. Extracellular polymeric substances (EPS) extracted from cathode effluent, analysed by 3D-EEM and FTIR, showed metal complexation capacity. However, excess Cu²⁺ caused cell deformation and lysis, as observed by TEM. These results indicate a concentration-dependent response with a critical toxicity threshold, providing a basis for operating bioelectrochemical systems treating copper-laden sulphate wastewater.