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 m3, 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 micromol mol(-1) in the compost piles of green waste, and up to 10 micromol 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 degrees C, including nonsterilized as well as sterilized samples. The concentration of CO was up to 160 micromol 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 CO2 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.

Soil-atmosphere CO exchanges and microbial biogeochemistry of CO transformations in a Brazilian agricultural ecosystem

Although anthropogenic land use has major impacts on the exchange of soil and atmosphere gas in general, relatively little is known about its impacts on carbon monoxide. We compared soil-atmosphere CO exchanges as a function of land use, crop type, and tillage treatment on an experimental farm in Parãna, Brazil, that is representative of regionally important agricultural ecosystems. Our results showed that cultivated soils consumed CO at rates between 3 and 6 mg of CO m(-2) day(-1), with no statistically significant effect of tillage method or crop. However, CO exchange for a pasture soil was near zero, and an unmanaged woodlot emitted CO at a rate of 9 mg of CO m(-2) day(-1). Neither nitrite, aluminum sulfate, nor methyl fluoride additions affected CO consumption by tilled or untilled soils from soybean plots, indicating that CO oxidation did not depend on ammonia oxidizers and that CO oxidation patterns differed in part from patterns reported for forest soils. The apparent K(m) for CO uptake, 5 to 11 ppm, was similar to values reported for temperate forest soils; V(max) values, approximately 1 micro g of CO g (dry weight)(-1) h(-1), were comparable for woodlot and cultivated soils in spite of the fact that the latter consumed CO under ambient conditions. Short-term (24-h) exposure to elevated levels of CO (10% CO) partially inhibited uptake at lower concentrations (i.e., 100 ppm), suggesting that the sensitivity to CO of microbial populations that are active in situ differs from that of known carboxydotrophs. Soil-free soybean and corn roots consumed CO when they were incubated with 100-ppm concentrations and produced CO when they were incubated with ambient concentrations. These results document for the first time a role for cultivated plant roots in the dynamics of CO in an agricultural ecosystem.

Attributes of atmospheric carbon monoxide oxidation by Maine forest soils

CO, one of the most important trace gases, regulates tropospheric methane, hydroxyl radical, and ozone contents. Ten to 25% of the estimated global CO flux may be consumed by soils annually. Depth profiles for (14)CO oxidation and CO concentration indicated that CO oxidation occurred primarily in surface soils and that photooxidation of soil organic matter did not necessarily contribute significantly to CO fluxes. Kinetic analyses revealed that the apparent K(m) was about 18 nM (17 ppm) and the V(max) was 6.9 micromol g (fresh weight)(-1) h(-1); the apparent K(m) was similar to the apparent K(m) for atmospheric methane consumption, but the V(max) was more than 100 times higher. Atmospheric CO oxidation responded sensitively to soil water regimes; decreases in water content in initially saturated soils resulted in increased uptake, and optimum uptake occurred at water contents of 30 to 60%. However, extended drying led to decreased uptake and net CO production. Rewetting could restore CO uptake, albeit with a pronounced hysteresis. The responses to changing temperatures indicated that the optimum temperature for net uptake was between 20 and 25 degrees C and that there was a transition to net production at temperatures above 30 degrees C. The responses to methyl fluoride and acetylene indicated that populations other than ammonia oxidizers and methanotrophs must be involved in forest soils. The response to acetylene was notable, since the strong initial inhibition was reversed after 12 h of incubation; in contrast, methyl fluoride did not have an inhibitory effect. Ammonium did not inhibit CO uptake; the level of nitrite inhibition was initially substantial, but nitrite inhibition was reversible over time. Nitrite inhibition appeared to occur through indirect effects based on abiological formation of NO.