Greenhouse gas emissions from green waste composting windrow.

The process of composting is a source of greenhouse gases (GHG) that contribute to climate change. We monitored three field-scale green waste compost windrows over a one-year period to measure the seasonal variance of the GHG fluxes. The compost pile that experienced the wettest and coolest weather had the highest average CH emission of 254±76gCday dry weight (DW) Mg and lowest average NO emission of 152±21mgNday DW Mgcompared to the other seasonal piles. The highest NO emissions (342±41mgNday DW Mg) came from the pile that underwent the driest and hottest weather. The compost windrow oxygen (O) concentration and moisture content were the most consistent factors predicting NO and CH emissions from all seasonal compost piles. Compared to NO, CH was a higher contributor to the overall global warming potential (GWP) expressed as CO equivalents (CO eq.). Therefore, CH mitigation practices, such as increasing O concentration in the compost windrows through moisture control, feedstock changes to increase porosity, and windrow turning, may reduce the overall GWP of composting. Based on the results of the present study, statewide total GHG emissions of green waste composting were estimated at 789,000Mg of CO eq., representing 2.1% of total annual GHG emissions of the California agricultural sector and 0.18% of the total state emissions.