Inhibition mechanisms of ammonia and sulfate in high-solids anaerobic digesters for food waste treatment: Microbial community and element distributions responses

The horizontal flow anaerobic digester indicated that high ammonia (2923 mg/L) and SO₄^2? (3653 mg/L) would influence the performance of methane production with food waste as substrates. Therefore, bottle anaerobic digestion reactors were carried out to investigate the effect of ammonia/sulfate concentrations on the methane production. Experimental results manifested that the anaerobic digesters with an ammonia concentration of 3500 mg/L or sulfate of 1600 mg/L showed the best performance of methane production, with an average methane yield of 0.32 and 0.33 L (g VS)^?1 d^?1, respectively. Specifically, a higher ammonia (6500 mg/L) or sulfate (1600-3500 mg/L) level hindered the bioconversion of C from liquid to gas phase (2.68% or 1.73% CH₄-Gas, respectively), while insignificantly for the hydrolyzation of C and N from solid to liquid phase. Similar to sulfate, high ammonia nitrogen seriously inhibited the methanation process, leading to a significant carbon accumulation in the anaerobic reactor, especially for propionic acid. The predominant archaea Methanosarcina at genus level indicated that aceticlastic methanogenesis was the major methanogenic pathway. Meanwhile, high ammonia level suppressed the activity of Methanosarcina, while modest sulfate improved H₂-consuming methanogens activity. A large fraction of unclassified bacteria within the Firmicutes (43.78%-63.17%) and Bacteroidetes (24.20%-33.30%) phylum played an important role in substrates hydrolysis.