The comparison of three nitrification filters in a recirculating system for Japanese flounder Paralichthys olivaceus culture

The growth and nitrification performances of plastic ring,volcano stone and oyster shell biofilter media were studied in a water recirculation system for Japanese flounder Paralichthys olivaceus culture by determination of the nitrogen concentrations of ammonia,nitrite and nitrate.Ammonia removal was compared in the same filter media 5,15,20,30,and 60 min after hydraulic retention.The nitrification kinetics and ammonia removal rate were studied by ammonia concentrations decreasing with time at different initial ammonia-N concentrations of 1,3,and 5 mg/L.The maturation time of the three types of filter media was found to be about 25 d.The maximal heterotrophic bacteria and the nitrite bacteria and the maximal active oxidation-reduction reaction were observed on the plastic ring among three types filter media,fowlled by on the volcano stone,then on the oyster shell.The optimum hydraulic retention period of the three types of filter media was found to be 20-30 min.The biodegradation of ammonia-N followed the zero-order kinetics in 12 h at the nitrogen load of 1 mg/L,and in 24 h at the nitrogen load of 3 mg/L or 5 mg/L.The ammonia removal rate by the three types of nitrification filter was 17.51-16.39,36.39-33.04,and 58.96-53.25 g/(m3·d) at nitrogen load of 1,3,5 mg/L.