Treatment Of Greenhouse Turtle Breeding Wastewater By Biological Filter-vegetable Hydroponic Cultivation System

Turtles breeding industry has become an important aquacultire industry in rural area especially in the Yangtze River Delta. industrial turtle breeding mainly conducted in the closed environment constant temperature. In order to keep turtles growing rapidly, the high-protein fish meal were used as main feed. Aquaculture wastewater contained a large number of high-protein feed and turtle feces because of low efficiency of utilization, which lead to high concentration of nitrogen and phosphorous in greenhouse turtle breeding wastewater. Greenhouse turtle breeding wastewater riched in nitrogen and phosphorous in rural areas was usually discharged into rivers and lakes without any treatment. Greenhouse turtle breeding wastewater not only brings much pressure on ecological environment, but also causes eutrophication and limits sustainable development of the turtle aquaculture. Based on the field survey of wastewater quality in the typical rural greenhouse turtle breeding farms, we designed a greenhouse turtle breeding wastewater treatment technology by combining biological nitrogen removal and soilless economic plant. Then we chose a typical intensive greenhouse turtle farm to carry out turtle breeding wastewater ecological treatment pilot. The conclusions were summarized as follows:(1) Greenhouse turtle breeding wastewater was neutral or slightly acidic, with high SS. The conductivity was 0.4-0.8ms/cm. CODcr,TN,TP changed greatly. CODcr changed greatly within the range 27.9-152.7 mg/L. The concentration of TN was 20～450 mg/L, The concentration of TP was 1.6～68.4 mg/L. C/N ratio of wastewater was less than 3, it could be classified as low C/N ratio wastewater.(2) Ipomoea aquatica Forsk, Brassicachinensis L, Lolium perenne, Brassica rapa L.Chinensis Group, Spinacia oleracea and Chinese lettuce were chosen as static experiment objects to compare N,P removal efficiency between each other. We found that the treatment effect of Ipomoea aquatica Forsk on nitrogen and phosphorous was the best. The removal ratio of NH4+-N, TN and TP reached 81.5%,83% and 96%.(3) We combined filler and plant floating-bed in a system to enhance the treatment efficiency of plant floating-bed. Ipomoea aquatica Forsk, Brassicachinensis L,and Chinese lettuce were chosen to study the wastewater treatment efficiency of combined system. The results showed that: CODcr removal efficiency of the system was above 90.0%, NH4+-N removal efficiency of the system was above 97.0%, TN removal efficiency of the system was above 73.9%, TP removal efficiency of the system was above 74.9%. Compared comprehensively, the treatment efficiency of Ipomoea aquatica Forsk and packing system was best, CODcr, TN and TP removal efficiencies were 95.6%,93.1% and 90.0% respectively.(4) Based on the design of biological filter- economic plants floating bed wastewater treatment system, we chose a typical greenhouse turtle farms to carry out pilot projects. The results show that:the technology was applicable in the treatment of greenhouse turtle aquaculture wastewater. The concentration of pollutants in the effluent could meet the requirement of secondary standard in Requirement for Water Discharge from Freshwater Aquaculture Pond (GB18918-2002), CODcr<40 mg/L, NH4+-N<2 mg/L, TN<5 mg/L, TP<1 mg/L.