Pilot plant studies were conducted on domestic wastewater to determine the feasibility of replacing conventional activated sludge gravitational clarifiers by dynamic straining. The dynamic strainers consisted of a rotating cylinder cleaned by an internal ultrasonic transducer. A primary strainer was placed and operated directly in the mixed liquor in the aeration tank. A secondary strainer was installed and operated in a separate tank to further clarify the effluent from the primary strainer. This work indicated that dynamic straining is a technically feasible process for replacing conventional activated sludge gravitational clarifers. Suspended solids removals of well over 99% were achieved with a single primary strainer operating in the pilot plant aerator with a mixed liquor suspended solids concentration of over 6,500 mg/l. When operated at lower specific flow rates, primary straining appears to be capable of consistently producing an effluent suspended solids in the 15-30 mg/l range. Present economic predictions indicate that plants equipped with primary and secondary dynamic strainers would cost more than plants utilizing conventional secondary gravity clarifiers. This factor can be tempered by several projected dynamic straining advantages. Two-stage dynamic straining has excellent application where space limitations exist. Secondary gravity clarifiers could be eliminated under the right conditions and aeration tank sizes could be appreciably smaller with the higher MLVSS concentrations achievable with dynamic straining.

Report prepared by FMC Corporation, Environmental Equipment Division, Itasca, Illinois. "Contract no. 68-03-0102; program element no. 1BB043." Includes bibliographical references (page 49).