Impact of biodegradation of organic matters on ammonia oxidation in compost.

Nitrification plays an important role in nitrogen turnover in composting process. It has been believed that nitrification occurs mainly during the maturation phase due to the elevated temperature during the active phase of composting. In this work, the intense biodegradation of organic matters is demonstrated to be another negative impact on the ammonia oxidation, the first step of nitrification. We investigated the ammonia oxidation in compost following organic matters addition at intermediate temperature. Different indicators of ammonia oxidation were studied, respectively. The accumulation of nitrite and nitrate was 10(2)-10(3) lower in composts with organic matters addition. The nitrous oxide emissions were absent or 40-fold inferior in these composts. The nitrogen mass balance indicated a less amount of oxidized ammonia after the addition. The ammonia-oxidizing bacteria declined following the organic matters addition. In contrast, the ammonia-oxidizing archaea were supported by the organic matters. Possible mechanisms of this impact were also discussed.

Nitrification and microbiological evolution during aerobic treatment of municipal solid wastes.

Nitrification is a key step in the nitrogen cycle in various ecosystems. In this study, the nitrogen dynamic and the evolution of groups of microorganisms were studied during aerobic treatment of fine organic fraction of municipal solid wastes. Mineralization of organic nitrogen exhibited two phases and resulted in two ammonia emissions peaks. The nitrogen balance indicated the onset of nitrification only during the maturation stage, which was confirmed by the accumulations of both nitrite and nitrate and the nitrous oxide emissions in this period. A significant development of ammonia-oxidizing bacteria correlated to the onset of nitrification. On the contrary, ammonia-oxidizing archaea were less abundant and declined through treatment. Identification of these ammonia oxidizers indicates that the Nitrosomonas europaea/eutropha-like ammonia oxidizing bacteria were responsible for ammonia oxidation instead of other groups of ammonia oxidizers during aerobic treatment of fine organic fraction of municipal solid wastes.