Greenhouse gas emissions from green waste composting windrow

摘要

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_4 emission of 254 ± 76 g C day~(-1) dry weight (DW) Mg~(-1) and lowest average N_2O emission of 152 ± 21 mg N day~(-1) DW Mg~(-1)compared to the other seasonal piles. The highest N_2O emissions (342 ± 41 mg N day~(-1) DW Mg~(-1)) came from the pile that underwent the driest and hottest weather. The compost windrow oxygen (O_2) concentration and moisture content were the most consistent factors predicting N_2O and CH_4 emissions from all seasonal compost piles. Compared to N_2O, CH_4 was a higher contributor to the overall global warming potential (GWP) expressed as CO_2 equivalents (CO_2 eq.). Therefore, CH_4 mitigation practices, such as increasing O_2 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 789,000 Mg of CO_2 eq., representing 2.1% of total annual GHG emissions of the California agricultural sector and 0.18% of the total state emissions.