Bioelectrochemical enhancement of anaerobic digestion under heavy metal stress: a comparative study of AD and AD-MEC systems

Abstract

Anaerobic digestion (AD) is a widely used technology for treating organic waste and producing renewable energy; however, environmental stresses, such as heavy-metal contamination, can significantly affect its stability. This study examines the potential of an integrated anaerobic digestion-microbial electrolysis cell (AD-MEC) system to enhance process resilience to heavy-metal toxicity. The performance of the AD-MEC was evaluated using cadmium (Cd-2(+)), copper (Cu-2(+)), nickel (Ni-2(+)), iron (Fe-2(+)), chromium (Cr-2(+)), and zinc (Zn-2(+)), and compared with that of a conventional AD system. The AD-MEC system exhibited greater resistance to heavy-metal inhibition, achieving higher maximum chemical oxygen demand (COD) removal efficiency and methane content than the conventional AD system. The order of heavy-metal inhibition was Zn-2(+) > Cu-2(+) > Cr-2(+) > Ni-2(+) > Cd-2(+) > Fe-2(+) for the traditional AD and Cu-2 > Cr2+ for the AD-MEC. These results highlight the potential of bioelectrochemical integration to enhance the robustness of anaerobic digestion under heavy-metal stress.