Meeting Secondary Effluent Standards at Peaking Factors of Five and Higher

Many wastewater treatment professionals equate secondary treatment with biological treatment. This viewpoint seems to be shared by much of the regulatory framework for wet weather treatment in the United States. Unfortunately, conventional biological treatment processes generally do not have a good track record of consistently meeting codified secondary treatment effluent limits at the high peaking factors associated with many wet weather events.Case studies are presented of two wastewater treatment plants (WWTPs) that use parallel treatment trains optimized to treat wet weather flows that exceed the capacity of their activated sludge process trains. These case studies demonstrate the effectiveness of this approach at consistently attaining secondary treatment effluent limits while under the influence of wet weather events. The results suggest that perhaps the wastewater treatment regulations should consider a more holistic view of secondary treatment and be more allowing of similar excess flow treatment strategies.