Changes in microbial biomass were monitored by measuring adenosine tri
phosphate (ATP) levels in a bench-scale composting bioreactor. Interna
l ATP standards were used in ATP bioluminescence assays to quantify th
e recovery efficiency. The ATP levels were comparable and found to be
within a range of 0.1 to 10 mu g/g dry wt compost in bioreactors maint
ained at 40, 50 and 60 degrees C. In compost experiments at 70 degrees
C, the estimated respiratory quotients suggested enhanced respiration
but the level of biomass measured as ATP decreased.