Settling and dewatering characteristics of mixed microorganisms according to changes in the SRT

This study was carried out to evaluate the settleability and dewaterability of mixed microorganisms according to the changes in sludge retention time (SRT) after mixing granulated methane-oxidizing bacteria and activated sludge (AS). The results of increasing SRT of microorganisms from 15 to 20 days showed that the settling rate of microorganisms increased, while specific resistance to filtration decreased. From the results of analyzing extracellular polymeric substances (EPS), no significant change was found in the bound EPS, but total soluble EPS showed a tendency to decrease as the SRT increased from 15 to 20 days. The average particle size of the mixed microorganisms was two to three times larger than that of the general AS, and as the SRT increased, the average particle size also increased, indicating that there is a close correlation between SRT and granule formation. The results of analyzing microbial community in SRT 15 and 20 days showed the dominance of Proteobacteria at long SRT.