Study On Thetreatment Of Turtle-breeding Wastewater Using Economic Plants Floating-bed System

China is the largest turtle-breeding and consumer countries in the world, and the production in Zhejiang province accounts for about50%of the total production in China. Turtle cultivation has become an important way of increasing farmers’ income and agricultural efficiency. Turtle cultivation in greenhouse was the main way of industrialized turtle-breeding with a high density, which conducted in the closed and constant temperature environment. In the intensive areas of turtle cultivation, the turtle-breeding wastewater was usually discharged into rivers and lakes without any treatment, and caused the eutrophication of reciving water badies. The discharge of wastewater not only has brought damage to the daily life and production safety of the surrounding residents, but also brought mush pressure on ecological environment and limits sustainable development of turtle aquaculture.Based on the field investigation of the breeding mode and wastewater quality of turtle aquaculture in the typical rural turtle-breeding farms, the wastewater was found that was low C/N ratio wastewater and that was difficult to treatment with biological denitrification. Therefore, we developed and optimized an economic plants floating-bed system to treat the wastewater. This research showed that economic plants floating-bed purification technology was an effective way to treat the wastewater, which is affordable, easy to maintain, high treatment efficient and energy efficient. Primary results were summarized as follows:(1) The uptake Kinetic characteristics of different ammonium and nitrate by celery were studied using modified depletion method. The kinetic characteristics of ammonium and nitrate uptake by celery could be illustrated with the Michaelis-Menten equation.The result showed that the Km for NO3-was lower than that for NH4+in celery, which showed that celery preferred NO3-on the low concentration of nitrogen. The Vmax for NO3-was higher than that for NH4+in celery, which showed that celery had higher NO3--N removal efficiency than NH4+-N on the high concentration of nitrogen. (2) Chinese cabbage, Italian lettuce and Apium graveolens were chosen as economic plants and compared for the purification effect of industrialized Turtle-breeding wastewater using ecological floating-bed system in glass greenhouse. The results showed that Chinese cabbage couldn’t adapt to the wastewater, however, celery and lettuce could adapt to the wastewater slowly and grow well. The lettuce floating bed system had a removal efficiency of ammonium nitrogen(NH4+-N)、chemical oxygen demand (CODcr)、total nitrogen (TN) and total phosphorus(TP) for98.9%,95.5%,95%and85.6%. For celery floating-bed system, the removal efficiency were97.2%,90%,80%and75%, respectively. Compared with the TN and TP removed from wastewater, the proportion is only14.9%and29.3%for the accumulation of TN and TP in lettuce, while the proportion is4.1%and7.9%in celery. Therefore, it showed that the Economic plants floating-bed system played an important role, not the vegetables,but the filler system.(3) The purification effect of industrialized turtle-breeding wastewater using celery ecological floating-bed system with intermittent aeration or circled-flow in glass greenhouse was investigated. The results showed that the way of intermittent aeration had a removal efficiency of NH4+-N,,CODcr,TN and TP for99.5%、98.2%、88.6%and84.6%after49days of test. For Circled-flow, the removal efficiency were97.2%、95.5%、73.9%and74.9%, respectively. For the accumulation of TP and total nitrogen TN in celery body, the dates treated by intermittent aeration were0.2and1.03mg·plant-1·d-1superior to0.098and0.9mg·plant-1·d-1by Circled-flow. The research showed that the intermittent aeration processing is better than Circled-flow and is energy saving.(4) Low temperature is a restrictive factor on purification of turtle-breeding wastewater by economic plants. In our environmental controlled laboratory, the purification capacity of economic vegetables for turtle-breeding wastewater under simulating the winter environment was studied. The results showed that the celery floating-bed system had a removal efficiency of NH4+-N, CODcr, TN and TP for97.7%,54.8%,94.6%and88.5%. For the green -vegetable floating-bed system, the removal efficiency were85.5%,50.3%,79.7%and70.7%。But, the removal rate of CODcr was very low between the two systems. And the phenomenon of shortcut nitrification was occurred in the system without vegetables,while the system with plants played an important role in making NO2--N no accumulation.(5) The performances of micro-aerated economic plants ecological floating-bed system (MEFBS) for treatment of turtle-breeding wastewater was investigated and the potential contribution of the system using different biofilm carrier was evaluated. The results showed that group C (Ipomoea aquatica Forsk and combined packing and Intermittent aeration) had promising removal efficiency ofNH4+-N,NO2-N, COD,TN and TP for88%、99.3%、84%、87.3%and73.7%after39days of test. And the purification efficiency was higher than in the group A(Ipomoea aquatica Forsk and Intermittent aeration) and the group D (Ipomoea aquatica Forsk and elastic stereoscopic packing and intermittent aeration) under the same conditions. The average net accumulation rate of TNin Ipomoea aquatica Forsk in group C was0.993superior to0.455and0.641mg·plant-1·d-1in group A and D. For TP,the dates were0.3、0.13and0.19mg·plant-1·d-1, respectively. Compared with group A、B and D, the group C could reduce turbidity value to a low level in a short time.(6) In a recirculating aquaculture system with single-lamp UV devices, experiments were carried out to investigate the effect of UV light on fecal coliform inactivation. The research results showed that UV intensity, recirculating flow rate and UV transmittance of water were three important factors for UV inactivation efficiency. It was found that the higher UV intensity, recirculating flow rate and UV transmittance of water made UV devices more effective. Based on the experimental data, a bacterial inactivation model of UV light for recirculating systems was presented and the first-order inactivation rate constant was found to be0.0062m2/J for UV inactivation of fecal coliform. The obtained results could be used for design and operation of UV inactivation in recirculating aquaculture systems.