Insight into effects of mature compost recycling on N2O emission and denitrification genes in sludge composting.

Mature compost recycling is widely used to reduce the dosage of organic bulking agent in actual composting process. In this study, the effects of mature compost amendment on N2O emission and denitrification genes were investigated in 47 days composting of sewage sludge and rice husks. The results showed that mature compost amendment dramatically augmented N2O emission rate in mesophilic phase and CO2 emission rate in thermophilic phase of composting, respectively. The cumulative amount of N2O emission increased by more than 23 times compared to the control. Mature compost amendment not only reduced moisture and pH, but also significantly increased NO3--N and NO2--N concentrations. The correlation matrices indicated that NO3--N, narG and norB were the main factors influencing N2O emission rate in sludge composting with mature compost recycling, but the N2O emission rate was significantly correlated to NO2--N, nirK and norB in the control.