Research On Key Technologies And Ecological Dredge Effects Of Taihu Lake

Taihu Lake is a typical shallow water lake and the accumulation of pollution sediment is serious. It could cause secondary pollution and seriously threaten the reliability of water supply. Based on the ecological dredge planning of Taihu lake, the cyanobacterial accumulation area, the formation region of "Hufan" and some important estuaries were selected as the the dredging regions. The dredging depth was determined by the monitoring results for sediment.According to the features and requirements of ecological dredge, pro-environmental cutter suction dredger was selected as the construction machinery. In China, the pro-environmental cutter suction dredger made by netherlands was widely used as dredging machinery. Based on the monitoring results for the impact scope determining, the disturbance of construction was not clear in the 5-10 m range around the reamer, and the disturbance was unobvious below 10 meters. Under the best conditions, the disturbance area of reamer was relatively unobvious in the spread radius of 5-10m and the spread could be enhanced by wind. The change of SS by reamer disturbance could change to be the previous levels in 4-5 min. GPS control was selected as the recommend mode for course control because of its smallest shallow point and high construction quality.The remaining water. treatment system of ecological dredge includes mud-dumping yard, sedimentation tank, chemical dosing system. The volume of mud-dumping yard is determined by the dredging quantity. For efficiently reducing engineering cost, the existing structural constructions was used as cofferdam. The removal of N and P by primary physical sedimentation process and chemical flocculation was discussed in this paper. The dredged sediment was treated using chemical solidification, low vacuum preloading and comprehensive utilization and it could be used as repairing basement of lakeside zone.A mass of pollution in sediment was removed by ecological dredge, especially serious pollution suspension mudflow on the surface of sediment. Through the ecological dredge,36 million m3 muck was removed. According to initial estimation, 2.15 million tons OM,29,000 tons TP and 92,000 tons TN were removed. Also, effective storage capacity of taihu lake was swell to 36 million m3. The implementation of ecological dredge could change the environmental conditions and the environment was changed from the anaerobic environment to the oxidation environment. These changes were benefit to sediment surface passivation and living environment of benthos. After the ecological dredge,70% kinds of benthos came back in 6 months and both of density and biomass were resumed by 61.8% and 64.0%. So, the ecological dredge area had the strong ability to recover. The ecological dredge technology could obviously reduce the phytoplankton biomass. But, it affected benthos and submerged plant in a certain degree. Furthermore, the life-form could restore to the former state in 1 to 2 years and the ecological structure in some part of the area could be improved.