Biochar combined with garbage enzyme enhances nitrogen conservation during sewage sludge composting: evidence from microbial community and enzyme activities related to ammoniation

Nitrogen loss is an unavoidable problem during composting processes, and the ammonia oxidation process significantly affects nitrogen transformation. The objective of this study was to evaluate nitrogen transformation when garbage enzyme (GE), biochar (BC), pelelith (PL) and combinations thereof were added during sewage sludge composting. Meanwhile, the succession of ammonia-oxidizing bacteria (AOB) and archaea (AOA) were also explored via quantitative polymerase chain reaction and high-throughput sequencing. The results showed that GE + BC and GE + PL treatments decreased ammonia (NH3) formation by 23.8% and 8.3%, and that of nitrous oxide (N2O) by 25.7% and 26.3% relative to the control, respectively. Simultaneously, the GE, GE + BC, and GE + PL treatments boosted the succession of AOA and AOB, and increased the activities of ammonia monooxygenase (AMO) and hydroxylamine oxidoreductase (HAO) activities and the gene copies of AOA and AOB. The AMO activities, NH4-N, NO3-N, and C/N, significantly affect AOA and AOB community structures. The network analysis predicted that the AMO and HAO were secreted mainly by the unclassified_Archaea and norank_Crenarchaeota, whereas it also showed that the GE + BC improved microbial associations with AOA, enzymatic activity, and environmental factors. Thus, the addition of garbage enzyme and biochar appears to be a promising mitigation strategy to reduce nitrogen losses during the composting process.