Reactor-Scale Characterisation of Nitrification in a Saline MBBR Under Live Mud Crab Loading

Saline attached-growth biofilters serving live crustacean cultures are seldom characterised with the quantitative tools of biological nitrogen-removal engineering. Two saline moving bed biofilm reactors (MBBRs) serving live mud crab (Scylla paramamosain) cultures ran for 65 days at nominal hydraulic retention times of 60 and 120 min, as independent case trajectories, not a replicated comparison. Through the 35 days of live-animal loading, both held total ammoniacal nitrogen removal above 85%, including across reduced-feeding, molting, and post-molt phases, with effluent near 0.07 mg L−1. Batch assays at ammonia saturation gave zero-order kinetics, apparent activation energies of 40.2 (95% CI 33.5–46.9) and 54.1 (46.6–61.6) kJ mol−1, and temperature coefficients θ = 1.055 and 1.075. Tracer testing confirmed near-completely-mixed hydraulics, so the biofilm experienced the effluent concentration: the reactor oxygen-to-nitrogen ratio exceeded 60 g O2 (g N)−1, the ammonia-limited regime, in which tertiary MBBRs show first-order, transport-controlled behaviour and a near-unity apparent temperature coefficient. The batch coefficients therefore describe the biofilm at saturation, not the operational rate-limiting step. Dual controls attributed essentially all nitrification to the carrier biofilm. Saline MBBRs and crustacean recirculating aquaculture systems have each been studied separately; their combination supplies design parameters for a regime absent from freshwater and synthetic-feed datasets.