Energy and economic advantages of simultaneous hydrogen and biogas production in microbial electrolysis cells as a function of the applied voltage and biomass content

Abstract

Energy and economic data on gaseous biofuel production in microbial electrolysis cells (MECs) can guide their installation, operation mode and modelling. Hydrogen and methane production from waste mainly depends on the cell voltage and biomass content in a bioelectrochemical system. In the present study, the energy efficiency and economic benefits of the simultaneous dual production of gaseous biofuels in a two-chamber MEC fed with digester effluents were established. Combinations of biomass content (5–75%) from dilution of the digester effluents and cell voltage (0.30–1.20 V) were tested for the simultaneous production of biogas in the anodic compartment and hydrogen in the cathodic compartment. The biogas volume reached 33 mL (2.5 mL d⁻¹) within 13 days and the hydrogen gas volume reached 3.5 mL (0.43 mL d⁻¹) within 8 days each in their corresponding compartment (135 mL). The highest energy efficiency based on hydrogen produced relative to the electrical input was 854%, which was obtained at 0.3 V and 40% biomass, while the highest methane production rate was 14.4 mL L⁻¹ d⁻¹ with a methane purity of 87% and was obtained at 0.43 V and 65% biomass. The highest economic gain was obtained through the production of biogas with a surplus of 20% due to the simultaneous production of hydrogen, reaching 0.010 USD per kg of chemical oxygen demand (COD) removed. The data generated in the comprehensive evaluation of the operating conditions can support decision making for future techno-economic studies.