Rotating Biological Contactors (RBC) have only recently been introduced in Japan as a means of providing secondary treatment to domestic wastewaters. The use of RBCs appears to be particularly attractive for small communities because of their low energy demand and reduced O-M requirements. To evaluate and demonstrate the feasibility of the process as an alternative to conventional secondary treatment, a field study was performed at three municipal facilities in Japan. A single, fundamental model of biofilm kinetics was shown to be capable of accurately predicting soluble BOD5 removals throughout the RBC. Model and field study results indicated that effluent soluble BOD5 should be 3 to 7 mg/l for conventional loads. Approximately 30 percent of the RBC effluent solids were found to be fine particles having a settling velocity of less than 10 to 15 m/day and which exerted 60 to 70 percent of the final effluent total BOD5. Therefore, special attention must he given to solids-liquid separation of the RBC effluent to ensure that the final effluent is of acceptable quality. Several solids-liquid separation methods, including direct screening of RBC effluent, were shown to be feasible in upgrading the effluent quality.

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