Macrogenomic analysis of the effects of aqueous-phase from hydrothermal carbonation of sewage sludge on nitrogen metabolism pathways and associated bacterial communities during composting

The effects of aqueous phases (AP) formed from hydrothermal carbonation of sewage sludge (with or without rice husk) as moisture regulators of nitrogen metabolism pathways during composting are currently unclear. Macrogenomic analyses revealed that both APs resulted in notably changes in bacterial communities during composting; increased levels of nitrogen assimilation, nitrification, and denitrification metabolic pathways; and decreased levels of nitrogen mineralization metabolic pathways. Genes associated with nitrogen assimilation and mineralization accounted for 34–41% and 32–40% of the annotated reads related to nitrogen cycling during composting, respectively, representing them as the most abundant nitrogen metabolism processes. The gudB and norB were identified as key genes for nitrogen mineralization and nitrous oxide emission, respectively. This research offers a better understanding of the effects of additional nitrogen sources on nitrogen metabolism pathways during composting.