Relationship between respiratory quotient, nitrification, and nitrous oxide emissions in a forced aerated composting process

• RQ can be an indicator of N2O emission in forced aerated composting process.
• Emission of N2O with nitrification was observed with RQ decrease.
• Mass balances demonstrated the RQ decrease was caused by nitrification.
• Conversion ratio of oxidized ammonia and total N to N2O were ∼2.7%.

We assessed the relationship between respiratory quotient (RQ) and nitrification and nitrous oxide (N2O) emission in forced aerated composting using lab-scale reactors. Relatively high RQ values from degradation of readily degradable organics initially occurred. RQ then stabilized at slightly lower values, then decreased. Continuous emission of N2O was observed during the RQ decrease. Correlation between nitrification and N2O emission shows that the latter was triggered by nitrification. Mass balances demonstrated that the O2 consumption of nitrification (∼24.8 mmol) was slightly higher than that of CO2 emission (∼20.0 mmol), indicating that the RQ decrease was caused by the occurrence of nitrification. Results indicate that RQ is a useful index, which not only reflects the bioavailability of organics but also predicts the occurrence of nitrification and N2O emission in forced aerated composting.