Impact of carrier on ammonia and organics removal from zero-discharge marine recirculating aquaculture system with sequencing batch biofilm reactor (SBBR)

Marine recirculating aquaculture system (MRAS) is an effective technology that provides sustainable farming of food fish globally. However, dissolved organics material (chemical oxygen demand, COD) and especially ammonia are produced from uneaten feed and metabolic wastes of fish. To purify the MRAS water, this study adopted a sequencing biofilm batch reactor (SBBR) and comparatively investigated the performances of four different carriers on ammonia and COD removal. Results indicated that the NH₄⁺-N removal rates were 0.045 ± 0.05, 0.065 ± 0.008, 0.089 ± 0.005, and 0.093 ± 0.003 kg/(m³·d), and the COD removal rates were 0.019 ± 0.010, 0.213 ± 0.010, 0.255 ± 0.015, and 0.322 ± 0.010 kg/(m³·d) in the SBBRs packed with porous plastic, bamboo ring, maifan stone, and ceramsite carriers, respectively. Among the four carriers, ceramsite exhibited the best performance for both NH₄⁺-N (80%) and COD (33%) removal after the SBBR reached the steady-state operation conditions. For all carriers studied, the NH₄⁺-N removal kinetics could be well simulated by the first-order model, and the NH₄⁺-N and COD removal rates were logarithmically correlated with the carrier's specific surface area. Due to its high ammonia removal, stable performance and easy operation, the ceramsite-packed SBBR is feasible for MRAS water treatment.