The Removal Performance Of Nitrogen In Constructed Wetlands And Nitrogen Budgets In Shrimp Ponds

Now shrimp farming adopts intensive and semi-intensive culture of high density , high water exchange rate, not only affect the surrounding ecological environment of aquaculture areas, but also bring about a good deal of disadvantage and potential harm for shrimp aquaculture. Consequently, the study and exploitation of low-carbon, efficient and environmental new models of culture wastewater treatment become the most urgent affair. Based on manifold auxiliary tests and obtained related data, practice experience, through production tests, the paper mainly studied the removal performance and characteristic of nitrogen in shrimp pond water with wetlands treatment and primarily discussed the nitrogen removal dynamics and nitrogen budget in shrimp pond with custructed wetlands treatment. The constructed wetlands consisted of slop area, emergening plants area and water storage pond, Pond water of 15% and 30% was recycled respectively with constructed wetlands at middle stage （65, 76 d） for 10 h, and late stage （91 d） for 20 h with flow 40 t/h. The hydraulic loading（HRL） of the constructed wetlands was 1.65 m/d, hydraulic retention time（HRT） was 0.417 d. During the operation of the wetlands, the wetlands play a certain effect on the removal of CODMn and different forms of nitrogens. TAN and TN were significantly （P<0.01） reduced by 37.9% and 26.7%, NO ?2 -N was significantly （P<0.05） reduced by 22.7%, NO₃^- -N and CODMn were reduced by 8.0% and 14.7%, respectively. NO₂^--N, TAN, NO₃^- -N and TN were significantly （P<0.01） reduced by 17.5%, 26.7%, 25.8%, 25.9% respectively after static for 6 h, 12h, 18h, 24 h. The pond water was mainly composed of total organic nitrogen （TON） and total inorganic nitrogen（TIN）. TIN was gradually removed by means of nitrification and denitrification and other ways during static. TON becomes the main components of TN after static for 52 h. TN was reduced by 57.9% after stay for 144 h. During stay period, the emergening plants area had a efficiency in removal different forms of nitro gens in wastewater. The removal of NO 2? -N, NO 3? -N, TN by making use of emerging plants area could be described using first-order kinetic model: Ct=C0exp（-kt）, k values were 0.0362 h^-1, 0.0291 h^-1, 0.0090 h^-1, respectively. Results showed that feed was the main sources of nitrogen inputs in E7 and E8 （control pond without wetland treatment）, accounting for 92.4% and 90.6% of total inputs, respectively. Within pond E7, 33.3% of the input N was converted to harvested shrimp, 30.8% remained in the sediment, and both were the main ways of nitrogen outputs. In addition, 6% of nitrogen outputs was remained in the constructed wetlands, and slope area and emergent plants area remained 63.7% of nitrogen remained by the whole wetlands. Within pond E8, 48.9% and 29.2% of the input N were settled down in sediment and converted to harvested shrimp, and the former was the main way of output N. The water chemical parameters were all maintained within a safe range during the culture period in E7 and the control pond （E8）. But E8 culture terminated at 77 d due to shrimp disease outbreak because of toxicity of microcystin, while E7 water was recycled respectively with constructed wetlands at middle stage （65, 76 d）, and late stage （91 d）, so microcystin was effectively controlled. At the end of experiment, mean body length and weight of Litopenaeus vannamei in E7 was 9.45 cm and 9.01 g, with the final yield 6.17 t/hm2, and these corresponding values in E8 were 6.85cm, 3.45g, 2.83 t/hm².The joint using constructed wetlands and new aerator, purified water network and Ceratophyllum demersum in shrimp pond, under the condition of no drugs and no exchanging water, the main water quality of shrimp pond was in range safety of shrimp growing during the whole culture period. Simultaneously, Microcystis aeruginosa may be efficiently restrained and removed, and shrimp aquaculture got good effect.Furthermore, Incomings and outgoings budget of dissolved oxygen in the Litopenaeus vannamei culture ponds with wetland regulation, and the effect of different culture water valume and culture days on the growth of Litopenaeus vannamei were studied. Results showed that The gross oxygen consumption of aquatic respiration was the largest oxygen consumer, then was shrimp respiration. The shrimp pond with constructed wetlands regulation showed more control ability on dissolved oxygen, and Microcystis aeruginosa may be efficiently restrained and removed with wetlands treatment.The study of the effect of different culture water volume on the growth of Litopenaeus vannamei suggested that higher culture yield of bottom shrimp could get through using more culture volume and placing hidden objects in the water. Feed was the main sources of nitrogen inputs in each groups, about 28.7%³7.6% nitrogen and 11.5%¹4.0% phosphors was settled in shrimps, and the rest turned into water, sediment and less was adsorbed and converted by purified water network. At last, waster water was discharged into surrounding water environment. This was one of the main reson of the eutrophication of water body. So, controlling feeding strictly was extremely important.The study of the status of the growth for Litopenaeus vannamei in different culture days suggested that mortality was highest in 20 d after starting shrimp culture. The water quality got remarkably worse from 50 d. Feed was the main sources of nitrogen inputs in each group, and the proportion gradually increased with culture period. Final water was the main sources of nitrogen outputs in each group. Nitrogen and phosphorus efficiency gradually decreased with culture period. The culture period from 40 to 60 days was the period of rapid growth. Feed input should be enhanced, but the feeding amount must be controlled in a fitting range.The study of the effect of different stocking densities on Macrobrachium rosenbergii suggested that the optimal stocking densities for Macrobrachium rosenbergii was 150⁴00 ind/m3.In addition, the changes in activity of digestive enzymes and immune enzyme in hepatopancreas of Litopenaeus vannamei at different growth stages and the effect of different culture water volume on the activity of enzymes mentioned above were preliminary discussed in this study.The small experiment mentioned above afford science and practice basis for making main experiment fluid and the result analysis.