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Abstract
The total ammonia nitrogen (TAN) concentration is often a key limiting water quality parameter in intensive aquaculture systems. Removing TAN through biological filtration is a major objective in the design of recirculating aquaculture systems. In this study, the effect of turbulent flow on nitrification rate was investigated using a reactor series system to improve nitrification efficiency by enhancing nutrient mass transfer. Nitrification performance of fixed-film biofilters was compared between the system with the diffusers placed inside the reactors (D-in) and that with the diffusers outside the reactors (D-out). The results indicated that the turbulence caused by diffused air had a substantial impact on the nitrification rate in the biofilters. When TAN concentration was not limited, the TAN removal rate in D-out reactors was 269 ± 58 mg/(m2 · d), only about 15% of that in the D-in reactors. These results suggest that increasing flow turbulence through air diffusion could be an effective way to improve the nitrification efficiency of fixed-film biofilters.