The Nitrogen And Phosphorus Removal In Recirculation System

The emissions of nitrogen and phosphorus of aquaculture are serious area source pollution. The development of recirculation system for aquaculture wastewater is one of trends on aquaculture in the future.In this paper, an aquaculture recirculation system of Paralichthys olivaceus was designed and built, including fish tanks, solids/liquid separation system, nitrification and denitrification filter and algae filter. The aquaculture recirculation system run for 130 days, the concentration of ammonia, nitrite, nitrate and phosphorus of fish tanks were less than 0.2,0.2,5.0 and 2.0 mg/L during the system operation, respectively. The growth of biological membrane on the plastic ring, volcano stone and oysters shell which are used as biofilter media were discussed by determining the concentration of ammonia, nitrite and nitrate. The removal of ammonia was compared under the different hydraulic retention time. Ammonia removal rate were studied. The results showed that the maturation time of three types of filter media were about 25d. The quantity of heterotrophic bacteria and the nitrite bacteria were the highest, and the activity of the oxidation-reduction reaction on the plastic ring was the best of three types filter media. The optimal hydraulic retention time of three types of filter media was in the range of 20-30 min; The ammonia removal rate of three types of nitrification filter was 17.51, 36.39 and 58.96 g/(m3·d) when the load of nitrogen was 1.0 mg/L,3mg/L and 5mg/L, respectively. The plastic ring were used as media of denitrification filter, the growth of biological membrane for denitrification were studied with the carbon source of residual baits and dejects of the sea cucumber by determining the concentration of nitrate nitrogen and TOC (Total Organic Carbon). The effects of denitrification for different carbon source were also compared under the optimal TOC/N. The results showed that the maturation time of biological membrane was about 17d, the nitrate removal rate of three types of carbon source was 24.50,25.99 and 28.26 g/(m3·d), respectively. At the same time, the nutrient removal of Ulva.pertus, Enteromorpha prolifera and Chondrus ocellatus was discussed. The ammonium removal of three macro-algae is consistent with the first-order dynamics, and velocity constants were 0.244,0.124 and 0.09/h, respectively. The removal rate of ammonia is much higher than that of the nitrate and phosphorus.