Bioelectrochemical Enhancement of Methanogenic Metabolism in Anaerobic Digestion of Food Waste Under Salt Stress Conditions

Abstract

Bioelectrochemical anaerobic digestion, a promising concept, has been proven to improve anaerobic digestion (AD) performance in methane production. However, it has been challenged by the unstable performances attributed to high-salt stress in food waste (FW). In this study, an Fe anode-assisted bioelectrochemical anaerobic digester (R1) was proposed to facilitate FW treatment. Batch experiments were conducted under different salt stresses to understand the impact of Fe-carbon microbial electrolysis cells on the performance of AD of FW. The results indicated that R1 achieved the highest specific methane yield of 0.15 L/g VS·day–1 as compared with the controls after being exposed to 20 g/L Na+. As demonstrated from metagenomic and metaproteomics analysis, the gene abundance and enzyme activity of salt-tolerant microbial communities were improved with the presence of an Fe anode in AD, which might be achieved by participating in the biosynthesis of key kinases or altering the metabolic pathways of cells. Methanothrix, a dominant species of salt-tolerant methanogenic archaea, could rely on CO2 reduction by using iron electrodes as an electron contact to facilitate methane metabolism. The enzyme of sodium transport ATPase 5 capability in excreting Na+ from the cell and regulating the cell penetration was enriched in R1, thereby significantly improving the salt tolerance under high salinities.