Urban wastewater oxidation by bioelectrochemical systems: To what extent does the inoculum matter?

Bioelectrochemical systems offer an environmental-friendly alternative to activated sludge for future wastewater treatment but have not yet reached technological maturity. This study aims to assess the long-term influence of the inoculation strategy on real urban wastewater treatment by bioelectrochemical systems, focusing on both process performances and biofilm assembly dynamics. Four inoculation strategies were investigated in triplicates during six consecutive batches to treat primary clarifier effluent at lab scale. At the studied anodic potential (0.05 vs SHE), no long-term impact of the inoculation strategy on the performances was observed. Indeed, after three batches, electrochemical (88.0 ± 3.9 % coulombic efficiencies) and treatment performances (30.8 ± 3.9 % COD removals) converged for all inoculation strategies. Consistently, the microbial compositions of the different biofilms converged, with selection being the main assembly process. For larger scale bioelectrochemical reactors, the use of wastewater as both substrate and inoculum would be the most convenient choice, since the other inoculation strategies only displayed short-term effects.