Suitable microbial indicators for ammonia inhibition detection

Ammonia inhibition in anaerobic digestion of food waste poses significant challenges for identification. Microbial indicators show promise in detecting ammonia-induced inhibition. However, their reliability remains limited due to unclear inhibition thresholds. This study proposes reliable microbial indicators through integrative analysis, including standardized ammonia inhibitory levels using the Hill model, metagenomic analysis, and a statistical framework. Results indicate that at non-inhibitory concentrations (< 2702 mg TAN/L), acetoclastic methanogenesis predominates, transitioning to hydrogenotrophic methanogenesis with syntrophic acetate oxidation. Inhibitory concentrations (2702 - 5805 mg TAN/L) impact denitrification, with nitrification, methylotrophic methanogenesis, and syntrophic activities prevailing, leading to acetate and propionate accumulation. At higher inhibitory concentrations (> 5805 mg TAN/L), hydrolysis and metabolism of various compounds are favored, potentially causing over-acidification. Suitable microbial indicators include Anaerolinea, Sphaerochaeta, Syntrophobacter, Methanomassiliicoccus, Methanosarcina, fhs, and acs. These indicators provide consistent responses for inferring inhibitory levels, offering early warning signs and insights into ammonia-affected metabolic pathways. They can be implemented in microbial management, aiding in ammonia effect detection, process monitoring, and countermeasure feasibility, contributing to the modernization of food waste digesters from a biological perspective