Study On Application Of Three Phase Biofluidized Bed In Tilapia (Oreochromis Niloticus) High Densities Recirculating System

Formation of biofilm, operation conditions and system stability of the InternalCirculation Three Phase Biofluidized Bed (ITFB) and its effect on high densitiesTilapia culturing were studied. The results were as follows:1. Treatment on simulated aquaculture wastewater with ITFB1) ITFB was prepared in the laboratory. In the experiment of biofilm formationthe optimal operation conditions were determined as follows: hydraulic retentiontime (HRT) was 0.5～2 h; Airflow rate was 2.5～7.5 L/min. The experiment of biofilmformation was carried out as HRT was 1.5 h and airflow rate was 5 L/min. TheResults were as follows: The biofilm showed up on media after 2 days and maturedcompletely after 10 days. The shapes of matured biofilm were various. Theintercellular jelly grew well. There ware many holes on the surface ofbiofilm.2) The experiment of biofilm formation was carrfied out as HRT was 1.5 h andairflow rate was 5 L/min. When the NH₄⁺-N concentration was 5 mg/L while CODconcentration was 10.57,19.45, 51.23, 112.22, 149.54 mg/L, respectively. The resuletsshowed that with the decreasing of COD concentration, removal rate of COD wasgradually promoted and then tended to decrease. When COD concentration was 51.23mg/L, removal rate of COD reached maximum of 82.13%. The dynamic equation ofCOD removal was V_COD=2.90[S]_COD/(0.067+[S]_COD). When the COD concentration was 50mg/L while NH₄⁺-N concentration was 1.18, 2.45, 5.12, 10.04, 14.89 mg/L,respectively. The resulets showed that removal rate of NH₄⁺-N reached maximum of82.56% when NH₄⁺-N concentration was 10.04 mg/L. With the increasing of NH₄⁺-Nconcentration, removal rate of NH₄⁺-N was gradually promoted and reachedmaximum. The dynamic equation of NH₄⁺-N removal was v_NH4+-N=0.61[S]_NH4+-N/(0.005+[S]_NH4+-N).2. Aplication of ITFB with high densities Tilapia culturing in arecirculating aquaculture system1) ITFB was Applied in high-density Tilapia culturing after biofilm formationwas completed successfully. HRT was 1.5 h; Airflow rate was 5 L/min. The initialculture density of Tilapia was 30.82 kg/m³. The test period was 100 d. Samples of culture water, influent and effluent water of ITFB were tested once per week. Theresults showed: ITFB maintained DO concentration in culture water and stabilizedpH value effectively. ITFB maintained concentration of NH₄⁺-N,NO₂^--N and CODwithin normal range. DO, pH value, NH₄⁺-N, NO₂^--N, NO₃^—N and COD in culturewere 3.68～6.17 mg/L,7.14～7.61, 0.5～1.11 mg/L,0.19～0.34 mg/L,4.59～12.35mg/L,9.77～23.57 mg/L, respectively.2) The growth indexes of Tilapia showed that: The average weight of Tilapiaincreased to 70.23g from 30.82g after 100 d. The terminal stocking density reached47.02 kg/m³ and the survival rate was 89.27%.