Biogas Upgradation in Second Generation Anaerobic Digestion: External Hydrogen-Mediated Biomethanation in Microbial Electrolysis System Coupled with Methanogenic Reactor.

Abstract

Biogas is a cutting-edge renewable energy source with significant market potential due to the widespread availability of organic biomass and is capable of assisting countries to achieve their sustainable development goals by facilitating the formation and availability of renewable energy sources. It has the potential to be utilized in order to generate electricity that can be delivered to electrical grids, or it can be used as a fuel for automobiles. Its low methane content is one of its limitations, despite its potential. So, to improve its efficiency, in-situ biogas upgradation can be done by the application of a next generation anaerobic digestion coupled microbial electrolysis system. MEC partially sustains the energy demand by electroactive oxidation of organic matter via a bioanode and facilitates CO2 reduction into CH4 by employing a biocathode as an electron donor. This study evaluates the impact of a microbial electrolysis system in an electromethanogenic reactor coupled with in situ biogas upgradation during two stage anaerobic digestion. The current study was performed in the reactor setups R3 having a single set of electrodes (SSE), R4 having a double set of electrodes (DSE), R5 having a single set of electrodes applied with voltage (MEC), and R6 having a double set of electrodes applied with voltage (MEC), in their methanogenic reactors, in which the gases were recirculated for the purpose of upgrading biogas, including hydrogen supplied from an external source and results were compared with control, R1 with no electrodes and no recirculation of gases (biogas and hydrogen), and R2 with recirculation of gases (biogas and hydrogen) with no electrodes. Improving the performance of the in-situ upgradation process involved optimization of the flow rate, recirculation time, and recirculation time with applied voltage. Methane content through recirculation recorded in R1, R2, R3, and R4 was 65, 87, 90, and 92% during interval-based time optimization. Maximum amount of methane content recoded was 95 and 99% in R5 and R6 with an applied voltage of 0.7V during interval-based time optimization. The conclusion of the study is that the addition of MEC with an enhanced surface area of electrodes can significantly enrich the methane content during upgradation in two stage anaerobic digestion.