Emissions of ammonia, nitrous oxide and methane during composting of organic household waste

In Sweden, composting of source-separated organic household waste is increasing, both domestically at the small-scale, and in larger municipal plants. Composting means a microbial decomposition of organic material, which results in the production of environmentally undesirable gases, such as ammonia (NH3), nitrous oxide (N2O) and methane (CH4). The aim of this thesis was to study the emissions of NH3, N2O and CH4 to the atmosphere during composting of source-separated organic household waste. The studies were conducted in an experimental reactor under constant and controlled conditions and in municipal compost heaps. Emissions of NH3, N2O and CH4 occurred at different phases during composting. Ammonia started to volatilise during the shift from mesophilic to thermophilic conditions when short-chained fatty acids were decomposed. Nitrous oxide was only emitted during the first days of composting and later during the cooling phase when nitrate was formed. Methane was only produced during the thermophilic phase. Large municipal compost heaps are a significant source for the production and emission of the greenhouse gases N2O and CH4. To avoid unwanted gaseous emissions to the atmosphere during composting, gaseous exchange with the atmosphere should be controlled in future composting plants