【作者】 张建华；

【导师】 郑正；

【作者基本信息】 南京大学 ， 环境工程， 2011， 博士

【摘要】 太湖是一个典型的浅水型湖泊,其污染底泥淤积严重,易造成湖体内源二次污染,引发湖泛生态危害,严重威胁太湖水源地的供水安全。实施生态清淤是减轻底泥内源污染的重要手段,也是太湖水环境综合治理的重要内容。根据国务院批复的《太湖水环境综合治理总体方案》和太湖生态清淤规划,选取蓝藻聚集区、湖泛易发区及重要入湖河口水域作为清淤的范围。根据太湖污染底泥多年系列监测资料,采用拐点法确定清淤的深度。根据生态清淤工程的特点和要求,推荐环保绞吸式挖泥船作为太湖生态清淤的施工机械。以目前国内已引进并大量应用的荷兰IHC公司生产的环保绞吸式挖泥船为主。通过对疏浚船绞刀影响范围的监测,距绞刀头5-10m范围施工扰动现象不明显,10m以外基本无影响。最佳操作条件下,绞刀对水体扰动总体影响较小,平静湖面最大扩散半径为5-10m,顺风方向扩散距离略有增大。监测表明,绞刀施工扰动使湖区水质SS值恢复至湖水本底值需4-5分钟。不同清淤精度控制方案表明,GPS控制形成的浅点数最小,施工质量最高,是平面和航向精度控制的推荐模式.生态清淤的余水处理系统由排泥场、余水沉淀池、加药系统等组成.排泥场容积根据清淤自然方容量确定,利用大堤等现有构筑物作为围堰,降低工程成本。采用“物理沉淀+化学絮凝”的组合方法去除余水中的氮、磷等污染物质。清淤的底泥以有机污染为主,可采用化学法、低位真空预压法固化,淤泥可用于建设湖滨带基底、大堤及绿化用土等,也可用于生产复合肥或制砖用土等。太湖生态清淤工程的实施,去除了污染底泥中所含的大量污染物质,尤其是表层污染较为严重的悬浮态流泥。以太湖底泥分布特征保守估计,太湖生态清淤污染物去除效益,全部工程清淤量约3600万m3完成后,初步估算清除湖内215万t OM,2.9万t TP,9.2万t TN。同时,直接增加太湖库容3600万m3。清淤工程的实施,使底泥表层的ORP由清淤前的厌氧(中度还原)环境改变至清淤后的中度氧化或氧化环境,对沉积物界面的钝化以及底生生物环境的改善都非常有益。生态清淤后仅半年清淤区已有70%种类的底栖生物得到恢复,底栖生物的密度和生物量也分别恢复61.8%和64.0%,说明疏浚区有较强的生物种群的自恢复能力；清淤工程可以明显减少浮游植物生物量；生态清淤对底栖动物、沉水植物有一定影响,但能在1—2年内得到恢复,且部分区域生态结构还能够得到优化。更多还原

【Abstract】 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.更多还原