SE—Structures and Environment

Gaseous emissions and the biological turnover of organic household wastes were studied under controlled conditions in a compost reactor (55°C, moisture content 65% w/w, O2concentration 16% in compost off-gas). During the first experiments, the temperature was increased to 55°C within 6 h using external heating. These experiments resulted in low emissions of CO2indicating a low biological activity. In order to achieve a representative composting process, the biomass was allowed to generate its own heat until the temperature reached 55°C. In this compost, the maximum CO2emission rate occurred at the change between the mesophilic and thermophilic phases. Fatty acids, present in household wastes, were only partially degraded in the externally heated compost. When the thermophilic phase began in the self-heated compost, fatty acids were decomposed followed by a rapid increase in pH and NH3emissions. The dynamics of fatty acid formation and decomposition seem to be important in controlling biological activity and thereby the gaseous emissions. Nitrogen emissions, consisting of more than 98% NH3-N and less than 2% N2O-N, amounted to 24–33% of the initial amount of N present in the self-heated composts. The outgoing gas from the reactor was cooled and more than 85% of nitrogen emissions were found in the condensate.