| A key to successful recirculating aquaculture system is the use of cost-effective water treatment system components. The biofiltration that has low energy cost and produces little excess sludge is widely applied in the water treatment of recirculating aquaculture system. Since the heart of any biofilter is the filter media, the type of filter media used strongly influences both the capital and operating costs of the biofilter. Although biofilters employing conventional natural and artificial non-toxic inert filter media such as gravel, fiber, dumped packings, structured packings have been used successfully in many applications, there is currently a need for further research on ways to optimize the properties of biofilter media. The manufacture and application of a novel functional biofilter media that has properties conducive to microorganism attachment and growth was of significance to the development of the recirculating aquaculture system.In the present study, based on the systematical study of the action and function of tourmaline in the aquacultural water treatment, a functional biofilter media (FBM) was prepared, and its applied effects was evaluated by the treatment of simulated aquaculture wastewater in Draft-Tube Three-Phase Fluidized Bed (DTFB).The results were as follows:1. Systematical study of the action and function of tourmaline in the aquacultural water treatment(1) The results showed that tourmaline controlled the pH values of seawater from 3 and 10 to 7.1 and 8.9, respectively. The increase of the pH value in low salinity solution was more than in high salinity of seawater and the finally pH values were all to about 8.0. The effect of tourmaline on the conductivity of the seawater was negligible. Factors affecting the regulating of seawater pH value, such as quantity of the tourmaline ,salinity and the initial pH value of seawater were also studied.(2) The treatment of chromium(Ⅲ) containing waster water using tourmaline wasexperimentally investigated. Results showed that Cr3+ could be removed effectively by tourmaline. Adding 2g tourmaline in 100 mL waster water containing 0 to 50 mg/L Cr3+, the removing rate of Cr3+ was more than 99% after 100 minutes. Initial pH value of waster water had no effect on the removing rate of Cr3+. Furthermore, the concentration of Cr3+ and pH value of the treated water both measured up the aquacultural demand. The tourmaline showed high repeated availability.(3) Methylene blue was selected as a model organic pollutant that was difficult to be degraded. The effectiveness of the tourmaline/I^Ch towards oxidative degradation of methylene blue was investigated. The results showed that methylene blue was remarkably degraded under the experimental conditions. It was found that the conversion rate was up to 99.1 % and the removal of COD reached 70 % when the initial concentrations of methylene blue was 5.34 X10"5 mol/L in the presence of 9.71 X 10"3 mol/L hydrogen peroxide and 20 g/L tourmaline at 60 °C for 150 min. The results showed that the degradation of methylene blue obeyed the pseudo-first order law.(4) Water molecules form an extended and dynamic hydrogen-bonded network. The structural change of water clusters can lead to multiple biological effects. Structural change of water clusters of distilled water induced by polar crystal tourmaline was observed. The results showed that tourmaline reduced 17O NMR full width at half maximum intensity (FWHM) for distilled water and the volume of clusters of water molecules.(5) Adding tourmaline into the medium, the growth of the Rhodopseudomonas palustris could be greatly promoted. The dehydrogenase activity was improved and remained stable under condition of pH ranged from 5 to 11 when tourmaline was added. Besides structural change of water clusters, the promoted activity of dehydrogenase may be caused by electrolysis of water and pH self-controlling induced by tourmaline.(6) The purpose of this trial was to improve the concentration of nitrifying bacteria by adding tourmaline into the media. The result showed that tourmaline had effect on the concentration of nitrifying bacteria and the nitrifying rate. Under the condition of 30 °C, p(DO) > 2mg/L, the concentration of nitrifying bacteria achieved 2.0 X 108 MPN pergram sludge after enriched and cultivated for three weeks.(7) To further study the effects of the tourmaline-treated-water on the aquatic animals, Caco-2 cells were used to investigate the effects of tourmaline-treated-Dulbecco's Modified Eagle Medium (DMEM) on the cell growth and the activity of alkaline phosphatase. The results showed the growth of cell was promoted and the activity of alkaline phosphatase was improved when tourmaline-treated-DMEM was used to incubate the cell.2. Preparation of a functional biofilter media (FBM) and its effects on thenitrifying bacteria growth and nitrificationFBM containing tourmaline was prepared. By analyzing the concentration of NH4+-N, NCV-N and NO3"- N in water, the performances of the PBM and FBM were determined. The results showed that the performances of FBM were better in term of the nitrifying bacteria growth and its nitrification. This study provided useful information that FBM has properties conducive to microorganism attachment and growth.3. The applied effects FBM as the biofilm carrier in the treatment of simulatedaquaculture wastewater in Draft-Tube Three-Phase Fluidized Bed (DTFB)(1) FBM and PBM were used as the biofilm carrier in DFTB to comparatively study the formation of biofilm. It was found that the biofiim on the FBM surface reached to 74 urn after 12 days of start-up and the COD removal rate was 81.21%, TAN maintained as high as 94.24%. The biofiim on the PBM surface reached to 74 um after 15 days of start-up, the COD removal rate and TAN were 81.62% and 84.72%, respectively.(2) The result of start-up showed that the hydraulic retention time (HRT), airflow rate and pH had effect on the biofilm formation. In this study, when HRT was 1~2 hours and the airflow rate was 10 L/min, the start-up of the reactor were successful. After the formation of the biofilm was finished, the treatment of simulated aquaculture wastewater was studied by changing the operating parameter. It was found that when the HRT was shorter, the removal of the COD and NH4+-N were better. The resultsindicated that by regulating HRT, the proportion of the neterotrophic bacteria and autotrophic nitrifying bacteria of DFTB, organic compounds and NH/-N of aquaculture wastewater could be effectively removed.
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