Comparison of GHG emissions during manure, biosolids and yard trimmings composting

Abstract. Emissions of GHG during the composting of different types of organic solid waste, including pig manure, dairy manure, chicken litter, biosolids and yard trimmings, were evaluated and compared under thermophilic conditions in this study. Duplicate compost reactors were loaded with approximately 1 kg (wet) of each feedstock adjusted to 60% moisture and a C:N ratio of 30 using cut straw. The results showed that the CO2 emission rate was highest during yard trimmings composting (83.44 g kg-1 DM d-1). The highest peak CH4 emission rate was observed during biosolids composting (59.16 mg kg-1 DM d-1). Chicken litter composting had the highest N2O emission rate (227.6 mg kg-1 DM d-1) which was much higher than that from other treatments. The majority of the initial carbon from all treatments was lost in the form of CO2 and this was found to contribute most of the total CO2-equivalent emissions. The highest carbon loss by CO2-C occurred in yard trimming composting (33.8%) and the highest cumulative nitrogen loss by N2O-N occurred from chicken litter composting (3.0%). The total GHG emission equivalent was highest during yard trimming composting (662.3 kg CO2-eq ton-1 DM) because of the highest CO2 emission (556.3 kg CO2-eq ton-1 DM) and the total GHG emission equivalent during chicken litter composting was the second highest (612.2 kg CO2-eq ton-1 DM) mainly owing to the highest N2O emission (307.5 kg CO2-eq ton-1 DM). When CO2 is not considered, then the CO2 equivalent emissions during composting were Chicken manure > >> Yard trimmings > Dairy manure > Biosolids.