Changes in chemical composition and microbial biomass during composting ofstraw and pig slurry

Composting was performed in an 800-L box and a 500-L, reactor system. The m aterial used was shredded straw of Miscanthus with pig slurry added as a ni trogen source. Chemical and microbial parameters were measured at five degr ee temperature intervals until the end of the heating phase and then with i ncreasing intervals during the remaining experiment. In both systems, major losses of carbon occurred during and after the thermophilic phase as a res ult of degradation of hemicellulose, followed by degradation of cellulose. Total amounts of phospholipid fatty acid (totPLFA) and adenosine triphospha te (ATP) were used as indirect estimates of microbial biomass. These method s correlated well over time, when the limitations of the method for the det ermination of ATP were taken into account. Microbial biomass in the two sys tems showed similar values when measured by totPLFA. In contrast, microbial biomass measured by ATP content was higher in the box system than in the r eactor system. In spite of the differences in chemical and physical propert ies in the two systems, the distribution of taxonomic groups of microorgani sms, indicated by marker PLFAs, showed similar patterns in the two systems, emphasising that in composting systems temperature is the major parameter controlling the composition of the microbial community.