Mitigation of ammonia inhibition in dry anaerobic digestion of chicken manure and corn straw using a self-developed gradient anaerobic digestion reactor

Dry anaerobic digestion (AD) is a promising technology for treating animal manure. However, it is often accompanied by ammonia inhibition, which decreases methane production. Optimizing feedstock ratios is an effective and economical strategy to mitigate ammonia inhibition in dry AD of chicken manure, but a thorough explanation and reactor optimization is lacking. This study investigated the performance of a self-developed gradient AD reactor (with a 16 % solid content). The AD experiment was conducted for 138 days over five phases, incorporating varying amounts of corn straw (20 %, 30 %, 40 %, 50 %, and 60 % based on total solids) to evaluate ammonia inhibition recovery and its underlying mechanisms. The results indicated that the highest methane yield (145.04 ± 3.48 mL/g∗VS) and content (60.67 ± 0.95 %) were achieved with chicken manure to corn straw ratio of 5:5 during Phase II. The population of key bacteria (e.g., Firmicutes, Bacteroidota) and methanogens (Methanosarcina) reduced significantly during Phase III and IV due to an increase in ammonia concentration (2869.71–4340.11 mg/L), leading to organic acid accumulation and methane yield reduction by 4.98 % and 71.14 %, respectively compared to Phase II. Metagenomic analysis further revealed that ammonia inhibition disrupted essential metabolic pathways, including substrate hydrolysis, metabolite transport, and methanogenesis. Upon returning to the feedstock ratio 5:5 in Phase V, the methane production rate recovered to 82.40 % of the initial level after 13 days. This recovery is probably attributed to enhancing key microbial abundances and methanogenesis metabolic levels through quorum sensing and self-regulation of two-component systems. These findings highlight the potential for optimizing feedstock ratios to improve the resilience and efficiency of dry AD systems.