1.1 Dredging equipment
The choice of dredging equipment directly determines the form of dredging: different dredging equipment has different disturbance degree to the bottom sediment, different diffusion and leakage performance, and different inhalation concentration. Therefore, the pollution of surrounding water caused by pollutants during construction is also different. At present, the research of the development of international environmental dredging equipment can be divided into two categories: the original dredger is used for transformation to meet the requirements of environmental protection construction; 2) special environmental protection dredging equipment.
Using the original dredger is a widely used method at present, which is economical and practical. The renovation of dredger focuses on dredging machine and positioning control, that is, replacing original dredging machine with environmental protection cutter, and equipped with advanced high-precision positioning and monitoring system to reduce secondary pollution in dredging process and meet the requirements of environmental protection dredging. From the technical point of view, the design and construction of special environmental protection equipment is not difficult, but from the economic point of view, the design and construction of special equipment is much higher than the transformation of traditional dredging equipment, and different projects need to build different equipment, for smaller projects, the economy is worse.
Environmental dredging equipment, the more advanced is the use of cutter suction dredger with environmental protection cutter. In this way, surface sediments are sucked up by the pipe directly under the action of the dredging pump and transported to the land for a long distance. All these dredging vessels are equipped with automatic control system and monitoring system, and DGPS is used for precise three-dimensional positioning, greatly improving the dredging accuracy. This method can reduce sediment re-suspension and release of pollutants.
1.2 Treatment of dredged sediment
The conventional disposal methods of dredging sediment mainly include stacking, dredging and ocean dumping. These disposal methods not only solve the problem of dredging outlet, but also generate various problems. Stacking treatment is mainly the problem of stacking site. stacking will take up a lot of land, and easy to produce secondary pollution. The dredging treatment is a method of comprehensive utilization of soil, which transports the excavated soil to the filling point. After water loss, silt is left to increase the elevation of the filled land. However, the foundation of dredger fill is generally very weak, which is not conducive to the later development and use of dredger fill. Meanwhile, dredger fill construction is easy to cause secondary pollution of the surrounding environment. Although the cost of ocean dumping is low, it will pollute the marine environment and destroy fisheries. Now many countries have legislated to prohibit it.
Dredging mud contains rich secondary minerals and is a good renewable resource. As the pollution source, dredging mud can be comprehensively developed and reused through a series of harmless and stable treatment methods, which can not only avoid the harm to the environment, but also produce new available resources. At present, dredged mud resource utilization technology mainly includes land use, building materials, filling materials, sewage treatment materials and hydrogen production.