Impact On Water Environment In Polluted Seriously Rivers In Suzhou By Different Dredging Degree

With the economy of development and rising of the people's living standard, urban pollution of rivers became severer and severer and the problem of sludge polluting need to be solved as soon as possible. At present, there were two different opinions on its ecological effects. The one was that the sludge dredging could improve the water quality and make for the recover of aquatic organism. The other was that the dredging cosmically and all sidedness would destroy the former water ecological system. For this reason and that all rivers dredging reached the hard sludge without researching on the rivers, the experts of this field put forward the better dredging depth of the polluted seriously rivers and that those rivers were need to be dredged ecologically. However, the study of this field were not enough.Based on the research background and the national tenth five magnitude project -- Suzhou City Water Environment Improvement and Synthesize Demonstration item, the static loading simulation test and the research of the dredging application in the polluted organically rivers of suzhou ancient city district was carried out. The impacts of different sludge dredging degree on the water ecological environment were analyzed, and main results and progressions in the experimental condition were illustrated as follows:(1) The final concentration of DTN and DTP in the overlying water decreased with the increase of the depth of sludge dredging, but nitrogen and phosphorous release rates were not in direct ratio with the dredging degree.(2) when TN, TP, OM of sludge was during respectively 1.3～2.5g/kg,1.1～ 2.0g/kg and 17～50g/kg, the nutrient content were decreased, the phytoplankton increase largely was restrained and the SD was increased, and the natural growth of Benthic algae and zoobenthos could be achieved.(3) The static planting test of Potamageton crispus and Hydrilla verticillata showed that it made for reducing the organical polluting degree,the reproduction of hydrophytic organism and aquatic organism when the TN, TP, OM of sludge were decreased to be during 1.3～2.5g/kg,1.0～2.0g/kg 和17～50g/kg.(4) In the polluted organically rivers of Suzhou ancient city district, when the TN, TP, OM of sludge were about 1.4g/kg,1g/kg and 25g/kg after sludge dreging, it could make for reducing the polluting degree of sludge, improving the water quality and recovering the submersed macrophyte.In conclusion, the sludge dredging could improve water quality and restore water ecological system and the better dredging depth of polluted seriously rivers in Suzhou was during 20～60cm, when the exterior contamination was controlled, the light and oxygen was satisfied. When TN, TP, OM in sludge after dredging were during respectively 1.3～2.5g/kg,1.0～2.0g/kg 和 17～50g/kg, the better dredging degree of endogenesis contaminated rivers of Suzhou ancient cities could be achieved.