N2O emissions during composting of organic waste (refereed)

During the process of composting organic waste, N losses in the range of 20-60% of the initial content occur. Possible emission pathways are losses to the atmosphere (NH3, N-2, N2O, NO) and losses to the hydrosphere (NO3- -leaching). The aim of the reported research was to examine the extent of N2O emissions during the entire process from collecting organic household garbage in containers through the different stages of composting. For this purpose two compost plants were chosen which had different process designs: an aerated continuous flow reactor and a batch compost heap. N2O production was measured by means of the flow-through chamber in the case of the continuous flow reactor and the closed cover method was used for the batch compost. During the entire process of collecting and composting, the N2O emissions showed pronounced dynamics with the maximum rate at the beginning of the thermophilic phase. However, the highest proportion of nitrous oxide was released in the curing phase because of its long duration. On average the total emission amounted to 42 mg N2O - N per kg composted dry matter. From this the potential contribution of composting organic waste originating from households, gardens and parks to the manmade N2O emissions in Germany was calculated to be very small (0.15 - 1.2%).