Adequacy assessment studies of improved circular clarifier for type-II settling for storm water treatment.

The adequacy of an improved circular clarifier was assessed for solids-liquid separation of chemically treated storm water. The storm water was treated with alum and polyelectrolyte to enhance settling. The performance of the clarifier was studied under various operating conditions by varying suspended solids concentrations and turbidity, and the hydraulic retention time. It was observed that the clarifier worked at an optimum hydraulic retention time of 1.5 hours for initial suspended solids concentration of less than 500 mg/L. However, for treatment of storm water with suspended solids concentration more than 500 mg/L, the hydraulic retention time needs to be selected taking the required effluent turbidity and effluent usage into consideration, i.e. for high turbidity removal an optimum hydraulic retention time of 2 hours must be used against a hydraulic retention time of 1.5 hours for a relatively low turbidity removal. Thus, the clarifier can be effectively used on field scale for solids-liquid separation of flocculent suspensions.