Bioelectrochemically-improved anaerobic digestion of fishery processing industrial wastewater

Anaerobic digestion (AD) is an environmentally friendly technology that can harness bioenergy from fishery processing wastewaters, which are usually treated with thermal and aerobic processes, yielding no coproduct. The integration of anaerobic digestion with a bioelectrochemical system (BES) represents a novel strategy to improve the overall stability, efficiency, and bioenergy recovery of the process. This study aims to evaluate the long-term performance of a 7.5 L AD-BES system treating real fishery processing wastewater as single substrate. It also examines the system's resilience to fluctuations in organic loading rate (OLR), extended periods of electrical and substrate starvation, and the progressive hydraulic disconnection of BES modules. Operated at an OLR of 0.6 gCOD L-1 day(-1) and a cell voltage of 0.7 V, the AD-BES demonstrated effective wastewater treatment and biogas production, achieving a chemical oxygen demand (COD) removal efficiency of 85-93% and a methane yield of 200-600 L-CH4 kg(COD)(-1). The system demonstrated resilience against OLR fluctuations, while prolonged electrical starvation periods (120 h and 192 h) did not determine any deterioration of the electrical response of the bioelectrodes. The progressive BES modules disconnection from the main AD reactor affected COD removal efficiency, volatile fatty acids (VFA) concentration in the digestate effluent, and methane content of the produced biogas, with minor impact in biogas production rate and yield. Microbial analysis indicated a high level of shared microbial sequences across the bioelectrodes biofilms and bulk liquid phases, indicating that the microbial community maintained the same functional roles within the different environments.