The Effect Of Constructed Wetland System By Water Quality Improvement Of Fish Pond

At present, the water shortage and water pollution is one of the major constraints for the sustainable development of social, economic, and ecological environment in many countries. The water eutrophication now is a common challenge for various countries around the world. Regarding the solving the challenge, physical method, chemical method and biological method are popularly adopted for water treatment. The former two methods are traditional ones with quick effect. But the operation cost is higher and it can cause secondary pollution. Therefore, physical method chemical method are not the optimal technologies for water treatment.Constructed wetland is a unique research unit which has bigger difference compared with natural one. Constructed wetland is an artificial ecosystem which is composed of substrate with one or several mediums in certain proportion, such as gravel, soil, coal cinder, etc, and aquatic plants growing in substrate. Substrate, aquatic plants and microorganism are the main components of constructed wetland.Constructed wetland system is a latest technology for waste water treatment. It’s an integrated technology which combines the physical, chemical and biological methods together. It achieves the purpose of reducing or removing nutrients and pollutants through a series of physiological and biochemical reactions of plants and microorganisms. The technology of constructed wetland is better than the traditional methods for water treatment because it is of following advantages:less investment, lower operating cost, higher efficiency and no secondary pollution, etc. In addition, aquatic plants in constructed wetland can beautify the environment and help the achievement of harmoniousness of landscape structures in city. That’s why the constructed wetland was widely applied to treatment of sewage from rural or urban areas, and waste water of industry and agriculture in developed countries, like countries in Europe and the United States. It’s believed that constructed wetland is playing an increasingly important role and presenting great potential in wastewater treatment. Moreover, constructed wetland can be used for treatment of various types of wastewater through equipping with different substrates and growing various plants.The research program was conducted in Wujin Aquaculture Farm of Changzhou city located in Taihu Lake basin. The total area of the farm is 3,395 mu. It has 212 intensive fish ponds with the area of 2,000 mu. Based on theory of ecology, the program established a recycling aquaculture system which was composed of constructed wetland and fish ponds. The constructed wetland was designed for the purification of eutrophic water from fish ponds. The channel bottom was dredged and its dyke was cemented. Three-grade constructed wetland system and aeration systems in fish ponds were established. The area of first-grade unit of constructed wetland is 175 mu,370 mu for second-grade unit and 30 mu for third-grade unit. According to circular economy theory and ecology, the system established ecological communities with high efficiency for water purification and diversified farming models. Some engineering measures, such as prohibiting the propagation of algae and forming artificial eco-membrane for filtration were adopted. Some techniques, like aeration, precipitation, growing aquatic plants, farming aquatic animals, propagation of microorganisms and equipping with substrate, were used for purification of wastewater from aquaculture step by step.The duration of the research program on the effect of recycling aquaculture system was six months. Water quality test was monthly conducted in constructed wetland and fish ponds. The results showed that the removal rate of total phosphorus for each month were 49.21%,78.35%,86.25%,78.35%,88.54% and 82.63% respectively. And the seasonal change within six months for the effect of water purification was significant (P< 0.05),while the removal rate of total phosphorus for each grade of constructed wetland are 71.21%,57.67% and 71.21% respectively; the removal rate of total nitrogen for each month were 59.89%,60.94%,63.35%,60.94%,73.08% and 64.89% respectively, while the removal rate of total nitrogen for each grade of constructed wetland were 46.97%,56.92% and 46.97% respectively; the removal rate of ammonium nitrogen for each month were 36.64%,49.91%,71.82%,49.91%,76.45% and 49.39% respectively, while the removal rate of ammonium nitrogen for each grade of constructed wetland were 14.29%,42.61% and 14.29% respectively; the removal rate of nitrate nitrogen for each month were 87.23%, 89.23%,86.57%,89.23%,94.57% and 83.33% respectively, while the removal rate of nitrate nitrogen for each grade of constructed wetland were 65.41%,81.59% and 65.41% respectively. In conclusion, the three-grade recycling ecosystem presented significant effect for purification of aquaculture water from fish ponds.