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 bio filters 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 sp heres with a density of 16 kg m(-3) with a specific surface area of 39 36 m(2) m(-3) (referred to as microbeads); and (2) 5.1 cm diameter pol yethylene packing material (Norpak) with a specific surface area of 16 4 m(2) m(-3). Nitrification rates increased linearly with influent tot al ammonia nitrogen (TAN) concentrations up to a concentration of 2.5 mg l(-1) for both the microbead and trickling filters. There was no fu rther increase in nitrification rate above 2.5 mg l(-1) that was stati stically significant. The trickling filter had a specific nitrificatio n rate 7.5 times higher than the microbead filter, although volumetric nitrification rates were 3.2 times greater for the microbeads than th e trickling filter. The study failed to show any relationship for eith er type of filter between the hydraulic loading rate and the nitrifica tion rate at hydraulic loading rates between 469 and 1231 m(3) m(-2) d ay(-1). (C) 1998 Elsevier Science B.V. All rights reserved.