Performance Evaluation of Rotating Biological Contactor Process

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.