Excess sludge reduction in activated sludge process through predation of Aeolosoma hemprichi

In this study, sludge reduction in a conventional activated sludge (CAS) process where Aeolosoma hemprichi (one species of oligochaeta) was inoculated as a micro-fauna was tested. The factors affecting the growth of A. hemprichi and the influence of A. hemprichi on treatment performance were investigated. The observed specific growth rate of A. hemprichi decreased at lower SRT, and the SRT at which A. hemprichi would be totally exhausted was estimated about 3 days. Obvious appearance of A. hemprichi was observed when the F/M ratio was lower than 0.7 mg-COD/(mg-VSS day). A. hemprichi grew independent of sludge concentration when SS concentration was higher than 300 mg-VSS/L, and more easily predated on sludge floes with higher protein content or smaller particle size. The apparent sludge yield was found to have a negative correlation with the density of A. hemprichi in the CAS reactor. The relative sludge reduction by A. hemprichi was estimated to be about 39-65%, and the apparent sludge reduction rate per unite weight of A. hemprichi was from 0.53 to 6.32 mg-VSS/(mg-A. hemprichi day). The existence of A. hemprichi was beneficial to stabilize the sludge settleability and TP removal but did not affect COD and NH4+-N removals in the process. The results indicated that using A. hemprichi to reduce sludge in wastewater treatment was feasible. (c) 2005 Elsevier B.V. All rights reserved.