Hyperthermophilic pretreatment composting can reduce ammonia emissions by controlling proteolytic bacterial community and the physicochemical properties

Proteolysis is the rate-limiting step in the mineralization of organic nitrogen into ammonium (NH4+) and thereby the ammonia (NH3) released during the composting. However, the dynamics of bacterial proteolytic communities related to NH3 emissions during the composting systems are mostly unknown. This study aimed to examine and compare the effects of hyperthermophilic pretreatment composting (HPC) and traditional composting (TC) methods on (i) the difference of NH3 loss and nitrogenous compounds; (ii) the dynamics of the proteolytic bacterial community involved in the proteolysis and (iii) the correlation between the proteolytic bacterial community, biophysiochemical characteristics and NH3 loss. Results revealed that the HPC decreased NH3 loss by 42% as compared to TC during 60-day composting period. This was accompanied with an inhibitory effect on protease activity in the HPC where the relative abundances of the proteolytic bacteria (Bacillus megaterium and Staphylococcus cohnii) were reduced significantly as compared to TC. Partial least-squares path modeling suggested that various physicochemical properties such as higher temperature as well as lower C/N ratio during composting played a dominant role in affecting the abundance of proteolytic bacteria, which may have been an important factor contributing to the lower NH3 loss in HPC. All these findings lead us to conclude that the HPC can significantly reduce NH3 loss by inhibiting the proteolytic bacteria and protease activity responsible for NH3 release.