Performance and operation of a rotating biological contactor in a tilapia recirculating aquaculture system

This paper describes the performance characteristics of an industrial-scale air-driven rotating biological contactor (RBC) installed in a recirculating aquaculture system (RAS) rearing tilapia at 28 °C. This three-staged RBC system was configured with stages 1 and 2 possessing approximately the same total surface area and stage 3 having approximately 25% smaller. The total surface area provided by the RBC equaled 13,380 m2. Ammonia removal efficiency averaged 31.5% per pass for all systems examined, which equated to an average (± standard deviation) total ammonia nitrogen (TAN) areal removal rate of 0.43 ± 0.16 g/m2/day. First-order ammonia removal rate (K1) constants for stages 1-3 were 2.4, 1.5, and 3.0 h−1, respectively. The nitrite first-order rate constants (K2) were higher, averaging 16.2 h−1 for stage 1, 7.7 h−1 for stage 2, and 9.0 h−1 stage 3. Dissolved organic carbon (DOC) levels decreased an averaged 6.6% per pass across the RBC. Concurrently, increasing influent DOC concentrations decreased ammonia removal efficiency. With respect to dissolved gas conditioning, the RBC system reduced carbon dioxide concentrations approximately 39% as the water flowed through the vessel. The cumulative feed burden - describes the mass of food delivered to the system per unit volume of freshwater added to the system daily - ranged between 5.5 and 7.3 kg feed/m3 of freshwater; however, there was no detectable relationship between the feed loading rate and ammonia oxidation performance.