Nonconductive anode-associated biocarrier achieved differentiated functional bacteria enrichment and relieved the competitive pressure on anodic biofilm of microbial electrolysis cells

Abstract

Microbial electrolysis cell (MEC) was an emerging technology for efficiently converting multifarious organic wastes to biogases (e.g. hydrogen and methane) with positive energy yield. The anode respiring process mediated by electrochemical active bacteria (EAB) in electrode biofilm was the key reaction in MECs. Yet, the anode has the trend to selectively enrich EAB (e.g. Geobacter sp.), which preferred simple organics. Feeding with relatively complex substrates, the EAB and fermentative bacteria competed on anode surface and formed biofilm stratification, which was adverse to the adjustment and synergistic interaction of those two functional bacteria. In this work, compensatory nonconductive biocarriers were equipped into MECs fed with sucrose to relieve the competitive pressure on anode by enriching differentiated functional bacteria on anode and nonconductive biocarriers, thus improving the overall organic degradation rate and current density. The addition of biocarrier reduced the cycle time by 35 % and improve the current density from 3.6 ± 0.3 to 5.3 ± 0.4 A/m−2 with non-fermented sucrose influent, while the COD removal and volatile fatty acids' utilization were also accelerated. With relatively complex substrates (fermented sucrose) in MECs, the fermentative bacteria were enriched on biocarriers, while the anode biofilm was domesticated for electrochemical activity with a much higher abundance of obligate EAB of 45.2 %. The nonconductive biocarriers in MECs could achieve biofilm differentiation and improve the synergistic interaction between EAB and fermentative bacteria. Achievements in this work provided a feasible method to improve the applicability of MEC technology in wastewater treatment of complex organics.