The inoculation of thermophilic heterotrophic nitrifiers improved the efficiency and reduced ammonia emission during sewage sludge composting

In this study, three thermophilic heterotrophic nitrifiers were isolated and inoculated into the semi-permeable membrane-covered composting of sewage sludge as thermophilic microbial (TM) agent. The physicochemical properties and microbial communities as well as the metabolism of microorganisms during composting were analyzed. Compared to CK, the inoculation of TM agent prolonged the thermophilic stage from 4 days to 7 days, increased the degradation of organic matters by 14.06 %, and promoted humification of compost. Meanwhile, TM agent reduced the NH3 emission by 34.64 % while the NO3--N content was 2.72 folds that of CK, resulting lower nitrogen loss. Additionally, an obvious succession of microbial communities occurred and the inoculation of TM agent enriched organic matters-degrading microorganisms (Bacillus, Thermobispora, Planifilum and Tepidimicrobium) and decreased the abundance of pathogens (Aspergillus and Cephalotrichum). Besides, many microorganisms related to nitrogen transformation were detected during the composting. The analysis of functional genes revealed that the nitrification was facilitated while denitrification process might be inhibited, establishing an efficient nitrogen retention system. This research provided an effective agent for sludge composting and indicated that the inoculation of thermophilic nitrifiers was a promising strategy to improve composting efficiency and reduce nitrogen loss.