Systematic and quantitative analysis of two decades of anodic wastewater treatment in bioelectrochemical reactors

Wastewater treatment is generally performed using energy-intensive processes, such as activated sludge. Improving energy efficiency has become one of the main challenges for next-generation wastewater treatment plants. Bioelectrochemical systems (BES) have been attracting attention because they take advantage of the chemical energy contained in wastewater while enabling the valorization of effluents: either with electrical energy (microbial fuel cells) or with useful chemicals (microbial electrolysis cells). Bioelectrochemical wastewater treatment has been under investigation since the early 2000s and is now the subject of an abundant literature, which is most frequently focused on anodic COD removal. Comparing results obtained in different studies is particularly difficult with BES, because many different parameters (effluent characteristics, inoculation, design, and operation) may interact and because using real effluents results in high variability. To address this issue, data were retrieved from 1,073 articles that were selected objectively and with transparency. This systematic review evaluates the potential of anodic wastewater treatment, based on 4,579 experimental observations. Overall, BES has already shown satisfactory treatment capacity, with a median chemical oxygen demand removal of 72%. However, the median coulombic efficiency was only 18%, increasing this parameter offers the greatest opportunity for BES improvement.