Abstract
The microbial community responsible for treating municipal sewage sludges (excess, anaerobic digested and solubilized sludge) by slurry composting was examined. The sludges were kept under isothermal aerobic conditions for two or three weeks, and then its microbial community was analyzed using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) or a PCR cloning assay targeting the 16S rRNA gene. The result of PCR-DGGE indicates that the microbial community changed significantly within one week. The number of detected clones indicated that Bacteroidetes- and Firmicutes-related organisms predominated. Their ratios were 32% and 48% in the excess sludge, 64% and 16% in the anaerobic digested sludge, 78% and 6% in the solubilized sludge, respectively. The predominance of these groups was also reported in organic wastes from other composting or degradation processes, particularly the late period of degradation. The microbial community change throughout the experimental period of slurry composting indicated that the Clostridiales-related (phylum Firmicutes) group is associated with particulate organic substrates, whereas the Flexibacter-or Chitinophaga-related (phylum Bacteroidetes) group is associated with dissolved organic substrates.
