Insights into high ammonia-resistant syntrophic microbiomes and metabolic pathways during continuous anaerobic digestion of cow manure

Abstract

Understanding microbial responses to ammonia is critical for defining thresholds and ensuring stable operation of anaerobic digestion (AD); however, an understanding of the microbiome's resistance mechanisms to high-total-ammonia–nitrogen (TAN) conditions remains limited. This study determined a TAN threshold of 7 g/L for continuous cow manure AD with increasing TAN levels. TAN was identified as the most critical factor influencing the AD performance, with CH4 production decreasing by > 50 % beyond this level. Additionally, a highly TAN-resistant syntrophic microbiome was identified through network analysis, highlighting key bacteria, Thauera phenolivorans and Fermentimons spp., alongside hydrogenotrophic methanogens. Interestingly, shifts were observed within the hydrogenotrophic methanogen community, transitioning from Methanoculleus bourgensis to Methanoculleus chikugoensis, Methanocorpusculum spp. and Methanobacterium spp. under high-TAN conditions. Significant metabolic pathways specific to high-TAN environments were identified, providing insights into their roles in sustained operation of AD. These findings highlight the performance limitations and functional redundancy under high-TAN conditions. © 2025 Elsevier Ltd