Composting of Source-Separated Household Organics At Different Oxygen Levels: Gaining an Understanding of the Emission Dynamics

Abstract

Source-separated household organics were composted in a reactor at three oxygen levels, 16%, 2.5% and 1% in the compost gas. Short-chained fatty acids were initially present in the compost material, and were also produced during the mesophilic phase at all three oxygen levels. This indicated that partial anaerobic conditions existed. No NH3 emissions occurred during the mesophilic phase due to acidic conditions. Composting at 2.5% and 1% O2 concentrations prolonged the mesophilic phase and reduced the microbial activity as compared to 16% O2. This led to delayed and decreased emissions of NH3. Nitrous oxide was not formed during thermophilic conditions. Methane, which was measured at 2.5% and 1% O2, was only found during thermophilic conditions. The emission of methane indicates that anaerobic conditions occurred during the thermophilic phase. The main reactions regulating pH during composting were outlined involving the ion species VFA, NH4+/NH3 and CO2/HCO3−/CO32−.