Mitigation Option of Greenhouse Gas Emissions from Livestock Manure Composting

Abstract

Composting of livestock manure is a significant source of greenhouse gases such as nitrous oxide (N₂O), but the complexity of the N₂O generation pathway hinders efforts to develop effective countermeasures. In this paper, we present one mitigation option for N₂O emissions from composting. Nitrite (NO₂^-) has an important role in N₂O generation. It has been observed that significant N₂O emissions from composting are induced when NO₂^- is accumulated during nitrification. Accordingly, in our technique, nitrite-oxidizing bacteria (NOB), as nitrifying bacteria, are added in the middle of composting fermentation to prevent NO₂^- accumulation. Adding NOB prevents prolonged NO₂^- accumulation, which had resulted in low N₂O emissions. This technique is also cost-effective, because mature compost can be used as an NOB source. Mitigating N₂O emissions allows more nitrate nitrogen (NO₃^-), of high value as fertilizer, to be preserved in the compost product. Moreover, it was confirmed that this technique could be combined with that for NH₃ mitigation using chemical reagents. Before actual use, it is necessary to investigate the methods used to determine optimal timing to add NOB source and prevent N₂O from being generated from an NO₃^- reduction.