Greenhouse gas emissions from windrow composting of organic wastes: Patterns and emissions factors

Direct emissions from commercial-scale composting are uncertain.We used micrometeorological methods to continuously measure greenhouse gas (CO 2 , CH 4 , N 2 O) emissions from full composting of green waste and manure.We measured oxygen (O 2 ), moisture, and temperature continuously inside the composting pile, and analyzed chemical and physical characteristics of the feedstock weekly as potential drivers of emissions.Temperature, moisture, and O 2 all varied significantly by week.Feedstock porosity, C:N, and potential N mineralization all declined significantly over time.Potential net nitrification remained near zero throughout.CH 4 and CO 2 fluxes, indicators of feedstock lability, were variable, and most emissions (75% and 50% respectively) occurred during the first three weeks of composting.Total CH 4 emitted was 1.7±0.32g CH 4 kg -1 feedstock, near the median literature value using different approaches (1.4 g CH 4 kg -1 ).N 2 O concentrations remained below the instrument detection.Oxygen, moisture and temperature exhibited threshold effects on CH 4 emissions.Net lifecycle emissions were negative (-690 g CO 2 -e kg -1 ), however, after considering avoided emissions and sinks.Managing composting piles to minimize methanogenesis-by maintaining sufficient O 2 concentrations, and focusing on the first three weeks-could reduce emissions, contributing to the climate change mitigation benefit of composting.