[Reducing sludge production by predation and its factors analysis in conventional activated sludge process].

Reducing excess sludge production induced by Oligochaete is carried out in a pilot scale of conventional activated sludge (CAS) reactor for 345 days. Worms occurred for nearly whole operating period except for the first 20 days, and continuously maintained at high density (over 30 total worms/mgVSS in aeration tank) for 172 days. Three types of worm were found, Aeolosoma hemprichicii and Nais elinguis alternatively dominated, but Pristina aequiseta occasionally presented. High worm density greatly contributes to both reducing sludge production and improving the sludge settling characteristics, and Nais elinguis had more potential for sludge reduction than Aeolosoma. Worm growth had impacts on effluent quality, and Nais elinguis growth affected effluent quality much more than Aeolosoma. Worm growth does not disturb the nitrification process, but PO4(3-) -P release into effluent occurres as Nais elinguis dominated. Analysis of factors affecting worm growth show that only SRT has no any impact on neither Aeolosoma nor Nais, however, both temperature and HRT can affect their growth very much.