Volatile Fatty Acid Production through Arresting Methanogenesis by Electro-Synthesized Hydrogen Peroxide in Anaerobic Digestion and Subsequent Recovery by Electrodialysis

Abstract

Producing volatile fatty acids (VFAs) in anaerobic digestion (AD) is of strong interest because of VFAs’ potential values in biomanufacturing. Despite some success of VFA production via pretreatment, in situ inhibition of methanogens for VFA accumulation has yet to be explored. Herein, a system consisting of hydrogen peroxide (H₂O₂) production, application of H₂O₂ for inhibiting methanogens in AD, and VFA separation was investigated. A polytetrafluoroethylene-based electrospinning electrode was synthesized and capable of generating ∼4.2 g L^–1 H₂O₂. When the generated H₂O₂ was applied to the AD, methanogens were inhibited, and VFA accumulation occurred. With the addition of 80 mg L^–1 H₂O₂, an average VFA concentration of 10.6 g COD L^–1 was obtained. The long-term H₂O₂ inhibition effect on methanogenesis was examined for nearly 100 days. A 2.3- to 3.3-fold increase in malondialdehyde levels, which indicated increased cell damage, along with a significant decrease in methane production and an increase in VFA concentration, might suggest that H₂O₂ could potentially inhibit methanogens while allowing acidogenic bacteria to remain functional. The accumulated VFAs were separated and then recovered using an electrodialysis unit, with a maximum VFA concentration of 26.7 g COD L^–1. The results of this study will encourage further exploration of the proposed system for VFA production by addressing several challenges, including a better understanding of the inhibition mechanism and a further increase in VFA yields.