Characteristics of Mesophilic Bacteria Isolated during Thermophilic Composting of Sewage Sludge.

The degree of inactivation by UV irradiation was different between vegetative cells and spores of bacteria isolated from sewage sludge composting at 60 degrees C. By using this property, a method to estimate the spore ratio of a mixture of vegetative cells and spores was presented. This UV irradiation method was applied to the estimation of the spore ratio of sewage sludge compost samples collected at several stages of composting. The spore ratio of mesophilic bacteria in the samples obtained at the thermophilic stage of 60 degrees C was 40% at most. The vegetative form of mesophilic bacteria showed a thermotolerance property at 60 degrees C by forming colonies but showed no respiratory activity at that temperature.