Emissions of N2O and CH4 from an aerated composting system were investigated using small-scale simulated reactors. The results show relatively high emissions of N2O at the beginning of composting, in proportion to the application amount of food waste. After 2 days, the N2O emission decreased to 0.53 ppmv on average, near to the background level in the atmosphere (0.45 ppmv). The addition of composted cattle manure increased N2O emissions not only at the beginning of composting, but also during the later period and resulted in two peak emission curves. Good correlation was observed between the N2O concentration at the air outlet and NO2/- concentration in waste, suggesting a generation pathway for N2O from NO2/- to N2O. Methane was only detected in treatments containing composted cattle manure. The high emission of methane illustrates the involvement of anoxic/anaerobic microorganisms with the addition of composted manure. The result suggests the existence of anoxic or anaerobic microsite inside the waste particles even though ventilation was employed during the composting process. (C) 2000 Elsevier Science B.V.