EVALUATION OF VARIOUS BIOFILTERS IN AN INTENSIVE RECIRCULATING FISH PRODUCTION FACILITY

Various types and combinations of biofilters were evaluated in an oper ating, full-scale intensive recirculating fish production facility. Ea ch of four tanks (18 900 L each) had a different combination of biofil ters: 1) four upflow sand filters; 2) one upflow sand filter and two f luidized bed sand filters; 3) two prototype floating-bead filters; and 4) one upflow sand filter and one rotating biological contactor (RBC) . The performance evaluation included the efficiency of each filter in removing total ammonia nitrogen (TAN), nitrite nitrogen (NO2-N), and suspended solids (SS). Removal was based on samples of the inflow and outflow of each filter taken once per day, two days per week for sever al weeks. Other water quality parameters measured were pH, alkalinity, carbon dioxide (CO2), and dissolved oxygen (DO). For periods of stabl e operation, mean removal rates of TAN, expressed as g TAN/day-(m(3) o f filtration media), varied from about 150 to 320 for the upflow sand filters, 250 to 290 for the fluidized bed sand filters, 120 to 160 for the floating-bead filters, and was 101 for the RBC. Standard deviatio ns about the mean were typically high (40 to 80% of the mean). Samplin g every four hours over a 24-h period showed substantial variability i n concentrations and nitrogen conversion rates. From a stability and r eliability standpoint, the most reliable nitrifying filter was the RBC . From a solids removal standpoint, the floating-bead filter was the m ost effective, generally removing 5 to 6 kg SS/day-(m(3) of filtration media). However, for each filter, items related to design and/or mana gement of the systems were identified which could be improved to incre ase stability and performance.