The effect of fixed film pretreatment on activated sludge stability during the treatment of cellulose acetate wastewater

Abstract

The activated sludge (AS) process used for treating high-strength cellulose acetate wastewater of Celanese Corporation, Pearisburg, Virginia, produces a sludge with poor flocculation and settling characteristics, particularly during the periods of shock organic loadings. Pilot-scale treatment units were set up to study the effects of a fixed film pretreatment on the stability of the AS process, using a new type of trickling filter (TF) media consisting of long plastic strips. The pretreated activated sludge (PAS) unit was compared with a control activated sludge unit (CAS). Different hydraulic and organic loadings were applied to the TF. The study confirmed the ability of a TF to provide greater stability to subsequent AS processes during periods of shock organic loading. The TF did not significantly improve the PAS system effluent quality and organic removal performance, even though the PAS sludge had better settle ability in terms of Sludge Volume Index and had less filamentous growth than the CAS system. The TF pretreatment confirmed its ability to act as a roughing filter. During the study, it reduced the organic loading on the AS system by 26 to 43 %, oxygen requirement of AS system by 38 to 62 %, the aeration volume requirement by 17 to 47 %, and the sludge production by 0 to 37 %. The PAS system required fewer nutrients than the CAS system.