DIAGNOSTIC APPLICATION OF STATE POINT ANALYSIS SOLVES CLARIFIER PROBLEMS

The Laguna Subregional Water Reclamation Facility (LSWRF) is a 20-mgd nitrification activated sludge facility owned and operated by the City of Santa Rosa, California. The activated sludge facility includes five circular, 115-feet (ft) diameter secondary clarifiers. The plant has historically experienced problems with solids washout in the secondary clarifiers during peak wet-weather events. A previous study of the problem had prescribed an increase in return activated sludge (RAS) pumping capacity as the solution to the problem. Accordingly, the City had embarked on a RAS Capacity Upgrade project to increase the RAS pumping capacity from 23 mgd to 55 mgd, at an estimated construction cost of approximately 3.3 million. A diagnostic evaluation of the problem using the State Point Analysis (SPA) technique revealed that the clarifier operational problems were caused not by RAS pumping capacity limitations, but by a Criterion II solids flux overload. The evaluation further showed that increasing RAS capacity would not address the problem with solids washout in the clarifiers. Instead, an operational strategy for wet-weather MLSS control was prescribed and used to successfully solve the problem. By allowing for an accurate diagnosis, the application of the SPA technique helped solved a troublesome operational problem, at the same time saving the City an estimated 3.3 million in construction cost.