Evaluation of the nitrification rates of microbead and trickling filters in an intensive recirculating tilapia production facility

Downflow floating polystyrene bead (microbead) and trickling media biofilters were tested simultaneously using common influent water from a 53-m(3) fish rearing tank stocked with tilapia (Oreochromis Nilotica x Aurea) at a density of 168 kg m(-3). The physical characteristics of the two bio-filter media used were: (1) 1.0 mm diameter polystyrene spheres with a density of 16 kg m(-3) with a specific surface area of 3936 m(2) m(-3) (referred to as microbeads); and (2) 5.1 cm diameter polyethylene packing material (Norpak) with a specific surface area of 164 m(2) m(-3). Nitrification rates increased linearly with influent total ammonia nitrogen (TAN) concentrations up to a concentration of 2.5 mg l(-1) for both the microbead and trickling filters. There was no further increase in nitrification rate above 2.5 mg l(-1) that was statistically significant. The trickling filter had a specific nitrification rate 7.5 times higher than the microbead filter, although volumetric nitrification rates were 3.2 times greater for the microbeads than the trickling filter. The study failed to show any relationship for either type of filter between the hydraulic loading rate and the nitrification rate at hydraulic loading rates between 469 and 1231 m(3) m(-2) day(-1). (C) 1998 Elsevier Science B.V. All rights reserved.