Activated sludge process is popular technology using complex microbes in wastewater treatment plants around the world. However, there is a big problem that the sludge does not settle easily after this process and poor settling causes carryover of sludge from the final effluent clarifies. It is called bulking, and this problem is a chronical problem. It is well known that bulking is caused by filamentous bacteria. In this study, we used two methods, fluorescence in situ hybridization (FISH) and real-time PCR, and try to identify a bacteria causing bulking.

　To identify bacteria causing bulking, we used two methods, FISH and real-time PCR. First, FISH is a cytogenetic technique and it dyes specific bacteria by FISH probes coupled complementarily with bacteria’s rRNA. We have identified the dominant filamentous bacteria in municipal wastewater treatment plants using the FISH probes. As a result, it is showed that Chroloflexi Type 1851 (Fig. 1) is a dominant filamentous bacteria in activated sludge. Moreover, revealed that the abundances of Chroloflexi Type 1851 filamentous bacteria in activated sludge, it is clear that increase in gene copy number of Type 1851 corresponded to a level of bulking it is called SVI. This suggests that proliferation of Chloroflexi type 1851 filamentous bacteria caused the bulking.

Fig.1　Chroloflexi Type 1851 filamentous bacteria