Carbon Monoxide from Composting due to Thermal Oxidation of Biomass

Emissions of carbon monoxide (CO) were observed from decomposing organic wastes and litter under laboratory, pilot composting plant, and natural conditions. Field studies included air from inside a compost heap of about 200 m 3 , emissions from composting of livestock wastes at a biologically operating farm, and leaf litter pile air samples. The concentration of CO was up to 120 μmol mol −1 in the compost piles of green waste, and up to 10 μmol mol −1 in flux chambers above livestock waste windrow composts. The mean CO flux rates were approximately 20 mg CO m −2 h −1 for compost heaps of green waste, and varied from 30 to 100 mg CO m −2 h −1 for fresh dung windrows. Laboratory studies using a temperature and ventilation‐controlled substrate container were performed to elucidate the origin of CO, and included hay samples of fixed moisture content at temperatures between 5 and 65°C, including nonsterilized as well as sterilized samples. The concentration of CO was up to 160 μmol mol −1 in these experiments, and Arrhenius‐type plot analyses resulted in activation energies of 65 kJ mol −1 for thermochemically produced CO from the nonsterilized compost substrate. Sterilized samples showed dramatically reduced CO 2 but virtually unchanged CO emissions, albeit at a slightly lower activation energy, likely a result of the high‐temperature sterilization. Though globally and regionally these CO emissions are only a minor source, thermochemically produced CO emissions might affect local air quality in and near composting facilities.