Alternating direction of catholyte forced-flow though 3D-electrodes improves start-up time in microbial electrosynthesis at applied high current density
Microbial electrosynthesis is an uprising concept for the combined carbon dioxide reduction and electricity storage in the form of chemical compounds. Although several proof of principle studies show great promise, mass-transfer limitations of substrates, protons and products remain one of the issues that needs to be tackled to bring the systems towards greater scale applications. A previously tested solution formed force flow-through catholyte recirculation, but this set-up encountered difficulties with gas accumulation during start-up at higher current densities (~-10 kA/m3), creating the need for a bypass to release gas. In this study, start-up at high current density was achieved by using an alternating flow-through regime. This regime decreased the operating energy input with 5% per kg of produced hydrogen and reached acetate production within 10 days after start-up at high current density. To study mass-transfer, local conditions (hydrogen, pH) were measured at the start and end of 60-days biotic experiments. The effect of the local conditions on the microbial community was also studied. The presence of C.kluyveri and unclassified Natranaerobiales were related to chain elongation activity, and the presence of M.arboriphilus was linked to methanogenesis activity. By identifying the effects of different flow-through strategies on local concentrations and functional microbial groups, this work provides insights on the optimal conditions for microbial CO2 conversion and highlight the application potential of microbial electrosynthesis.