Enhanced stability and performance from food waste leachate under ammonia stress via constructing a novel two-phase anaerobic digestion system

High ammonia stress and high organic loading rate (OLR) are considered as the inhibitors to the anaerobic digestion (AD) system. To enhance methane production and stabilize the AD system for high OLR and high ammonia concentration food waste (FW) treatment, a novel two-phase AD system consisting of a homo-acetogen-dominated ambient acidogenic system and methanogenic system enriched with syntrophic acetate-oxidizing bacteria (SAOB) was established. The results showed that the two-phase AD system obtained better performance including methane yield and gas production, which were 176.79%-107.59% and 87.86% higher than control group under 7000 mg COD/L. Homo-acetogens Acetobacterium played a key role on acetate generation and exhibited a relatively high abundance (21.60%) at high OLR. Additionally, SAOB, specifically Syntrophobacter and Thermovirga, enriched in the methanogenic system, and their relative abundance increased by 9.80% and 8.63% under ammonia stress. The PICRUSt analysis showed that the key functional enzyme-encoding gene Acetyl-CoA decarbonylase/synthase and acetate kinase, which related to hydrogenotrophic methanogenesis and acetate generation, respectively, both presented higher relative abundance under ammonia stress. Overall, our study demonstrates that the constructed novel two-phase AD system has significant superiority on the stability and CH4 generation compared to traditional AD system. This study highlights the effects of domestication on the treatment of FW leachate, emphasizing the optimization of two-phase AD process.