Computational and experimental analysis of organic degradation positively regulated by bioelectrochemistry in an anaerobic bioreactor system

Abstract

Methane production was tested in membrane-less microbial electrolysis cells (MECs) under closed-circuit (RCC) and open-circuit (ROC) conditions, using glucose as a substrate, to understand the regulatory effects of bioelectrochemistry in anaerobic digestion systems. A dynamic model was built to simulate methane productions and microbial dynamics of functional populations, which were colonized in groups RCC and ROC during the start-up stage. The experiment results showed significantly greater methane production in RCC than ROC, the average methane production of RCC was 0.131 m3/m3/d, which was 1.4 times higher than that of ROC (0.055 m3/m3/d). The simulation results revealed that bioelectrochemistry had a significant influence on the abundance of microorganisms involved in acidogenesis and methanogenesis. The abundance of glucose-uptaking microorganisms was 87% of the total biomass in ROC without applied voltage, which was 20% higher than that in RCC (67%) when external voltages were applied between the anode and cathode. The abundance of hydrogenotrophic methanogens in RCC was 6% higher than that in ROC. The simulation results were verified through 16S rDNA high-throughput sequencing analysis. An electron balance analysis revealed that alteration of the acidogenesis type led to more acetate and hydrogen production from glucose fermentation, compared with the situation without bioelectrochemistry. An additional pathway from acetate to hydrogen was introduced by bioelectrolysis. These two factors resulted in significant enhancement of methane production in RCC. Bioelectrolysis process directly contributed to 26% of the total methane production after the start-up stage. When the applied voltages were cut down or decreased, RCC could maintain considerable methane productions, because the microbial communities and electron transfer pathways were already formed. Starting-up with high voltage, but operating under low voltage, could be an energy-favorable strategy for accelerating biogas production in bioelectro-anaerobic bioreactors.