Metabolic mechanism of thermal pretreatment combined with ethanol pre-fermentation to enhance anaerobic digestion of food waste: A comprehensive analysis of key enzyme-encoding genes

Ethanol pre-fermentation (EP) can enhance methanogenic efficiency and facilitate food waste (FW) hydrolysis, while ensuring anaerobic digestion (AD) system stability. FW contains high-water content, and thermal pretreatment (TP) can significantly enhance solids and soluble organic matter content. The study focused on investigating the mechanism of TP combined with EP (TP-EP) on the AD of FW. The results showed that TP-EP enriched hydrolyzing and acid-producing bacteria, as well as the methanogens Methanosarcina, and Methanothrix. Consequently, the degradation rates of soluble chemical oxygen demand, volatile fatty acids, and cumulative methane yield exhibited an increase of 9.54%, 5.94%, and 20.42%, respectively, in comparison to the control. EP promoted carbohydrate metabolism, while TP promoted amino acid metabolism and enhanced energy metabolism by enriching F-type ATPase and NADHase. When combined as TP-EP, the processes integrated the advantages and promoted substrate hydrolysis and energy metabolism while enhancing methanogenic metabolism.