An evaluation of commercially available biological filters for recirculating aquaculture systems

Three different commercially available biological filters were evaluated in triplicate on a 60 m3 tank-based Tilapia system under commercial warmwater growout conditions. The study was performed at the North Carolina State University Fish Barn—a commercial scale research and demonstration recirculating aquaculture facility operated by the department of Biological and Agricultural Engineering. Total ammoniacal nitrogen (TAN) removal rates were determined for the three types of biofilters for a range of concentrations ranging from 0.13 to 1.20 g TAN m−3. TAN concentrations were varied by feed rates and ammonium chloride additions, and limited by fish feeding response. Maximum feed rates were 65 kg feed d−1 using a 40% protein diet at a maximum biomass of 5500 kg. Average observed TAN removal rates (in g TAN m−3 of unexpanded media d−1 ± standard deviation) for the three filters were 267 ± 123, 586 ± 284, and 667 ± 344 for the moving bed bioreactor, floating bead filter, and fluidized sand filter, respectively. These results are considerably lower than results previously published at the laboratory scale using artificial waste nutrients. This study highlights the need for future biofilter evaluations at the commercial scale using real aquaculture waste nutrients.