Variation Of Water Quality And The In-situ Water Quality Improvement Of A Stratified,Source Water Reservoir

With accelerated urbanization in China,the contradiction between water resources protection and economic development is becoming more and more serious.As the main source of drinking water,surface water such as reservoir has received increasing attention.However,increasingly serious water quality degradation and eutrophication not only have a significant effect on the quality and safety of urban water supply,but also greatly raise the cost of water treatment.Therefore,the evolution law and technology improvement of urban water quality have become an important topic.In this paper,with Zhoucun reservoir as subject,field monitoring combined with laboratory analysis method was applied to analyze and investigate the characteristics of water pollution,and the law of thermal stratification as well as sediment release;on this basis,the feasibility and effect of the application of water-lifting aeration system in water quality improvement in situ were studied,and main research conclusion included:The characteristics of water pollution and sources of pollutants in Zhoucun reservoir were clarified: April~mid-May of each year was a layer formation period,during which gradually formed water temperature gradient effectively limited the substance exchange in vertical water body,and accelerated the transition to anaerobic state in the bottom water.Water pollution in reservoir presented a seasonal characteristic: a massive outbreak of algae as well as high ammonia nitrogen,heavy metal and odor pollution in the bottom water were observed in summer-autumn high-temperature seasons annually.The analysis of pollution sources revealed that ammonia nitrogen,total phosphorus,manganese and sulfide pollution at the lower level of water body of the reservoir was from the release of endogenous pollutants from sediments;and nitrate nitrogen and total phosphorus in the surface water body of the reservoir mainly came from reservoir runoff from upstream.The characteristics of oxygen consumption by sediments and the release characteristics of cyclic transformation of nitrogen,phosphorus and sulfide under in situ condition were explored: the dissolved oxygen in the overlying water could be consumed by sediments in a short time,with oxygen consumption rate reaching 16.14-20.14 mg/(m2·h).The improvement in water-lifting aeration system: 1)aeration chamber length was extended,the contact time between compressed air and anaerobic water was prolonged,and oxygen utilization ratio was enhanced;2)high-efficient micro-porous aeration device was applied replacing perforated pipe aeration device to increase oxygen transfer efficiency;3)horizontal diversion diffusion disc and oxygen filling range in bottom water were expanded;pneumatic cutting device was added,the outlet flow and the energy of gas bomb of the water-lifting aeration system were made full use of,and mixing effect on water body was strengthened.Based on the new-type water-lifting aerator,in situ water quality improvement demonstration project was constructed in the reservoir.Verify and complete the mechanism of the full cycle in reservoir induced by water-lifting aerator.The formation of the full circulation,is the use of the characteristics that the indirect action area water stratification state changes slowly,the bottom water temperature rise relative slow than that of direct action area.Due to the different temperature,the density difference between the bottom water in the two areas result in stratified flow density,indirect action area water flow to the direct action area,causing the full circulation in the reservoir.The operation of the demonstration project completely reversed the anaerobic environment of the bottom water and significantly inhibited the release of pollutants from sediments in a short time.After the operation of water-lifting aeration system for 30 days,mixing advanced in the reservoir,and ammonia nitrogen,total phosphorus and manganese concentrations in the vertical water body decreased significantly to 0.261 mg/L,0.071 mg/L and 0.253 mg/L,respectively(decreased by 89.4%,84.4% and 87.1%,respectively,as compared with the levels before the operation);the reduction rate of sulfide and sulfur-containing odorous compounds reached 97-99%,suggesting an effective solution of the odor problem in water.