Adapting microbial communities to low anode potentials improves performance of MECs at negative potentials

Abstract

A unique aspect of microbial electrolysis cells is the use of an applied voltage for H2 production. A variation on this parameter is the use of a controlled anode potential rather than controlled cell voltage, which can result in a more stable redox environment for the anode microbes. In this study, long-term exposure of anode consortia at −400mV and 0mV vs. Ag/AgCl resulted in a gradual divergence of the resulting bioanode midpoint potentials by >100mV over a 6-month period. Cyclic voltammetry revealed a shift in peak current production to more negative potentials for the reactor poised at −400mV. Furthermore, chronopotentiometry indicated very different profiles, showing a difference of 500mV in the potential required to achieve a current of 15mA (equivalent to 12A/m2). A 3-fold higher current was observed at a poised potential of −400mV for the anode enriched at a poised potential of −400mV, compared to that enriched at 0mV. The substrate used was a bio-oil aqueous phase (BOAP) derived from switchgrass, making this study unique with potential for biorefinery application in producing hydrogen, fuels or chemicals. Operation at −400mV resulted in a 1.5-fold higher electrical efficiency reaching 164.9%, while marginally reducing hydrogen recovery by 1.0%. The results provide evidence for adaptation of complex communities to optimize applied potential, while reducing energy input for electrolysis. The community developed here has potential to be explored further to understand complex community-function relationships.