Semi-continuous mesophilic-thermophilic two-phase anaerobic co-digestion of food waste and spent mushroom substance: Methanogenic performance, microbial, and metagenomic analysis

[Display omitted] •EP-MP system increased average CH4 yield of co-digestion by 1.91–2.43 times.•Hydrolytic acid-producing bacteria and methanogens were enriched in EP-MP system.•Key genes related with substrates metabolism were up-regulated in EP-MP system.•Metabolic pathways were affected to benefit acetate and acetyl-CoA synthesis.•CH4 production was enhanced by the synthesis of acetate, formate, and CO2/H2. The methanogenic efficiency and system stability of anaerobic co-digestion of food waste (FW) and spent mushroom substance (SMS) are important for its application. A 90-day semi-continuous study was conducted to compare the co-digestion performance of an ethanologenic-methanogenic two-phase system and an acidogenic-methanogenic system using FW and SMS as substrates. The results showed that the ethanologenic-methanogenic system increased the contents of ethanol and acetate in the hydrolytic acidification phase. Microbial-community analysis showed that ethanologenic-methanogenic system enriched hydrolytic acidifying bacteria and methanogens such as Methanoculleus, resulting in an increase in the average methane yield of methanogenic phase by 1.91–2.43 times at the same organic loading rate (OLR = 3.0–4.0 g-VS·L-1·d-1). Metagenomic analysis indicated that the ethanologenic-methanogenic system increased the abundance of enzyme-encoding genes and promoted the degradation of acetate and CO2/H2, thereby enhancing methanogenic metabolic pathways, compared to the acidogenic-methanogenic system.