With the continuous improvement of people’s awareness of environmental protection, great progress has been made in the control of exogenous pollution in rivers, lakes, oceans and other waters. After the external pollution is effectively controlled, it is one of the effective methods to remove the internal pollution by environmental dredging. This paper discusses the basic concept and technical requirements of environmental dredging and introduces the engineering characteristics of environmental dredging.

1. Introduction

Environmental protection is one of the hottest topics in this century. All countries and regions in the world have invested a lot of manpower, material resources and financial resources in resource protection and environmental protection. China is a developing country with a large population, with many lakes and rivers, among which there are serious water pollution problems. As people pay more and more attention to environmental protection, the construction concept of environmental dredging comes into being. Environmental dredging is a newly developed industry, which belongs to the cross-discipline and construction technology of ocean engineering, water transportation engineering, environmental engineering and dredging engineering. It is one of the most effective ways to improve the water environment by environmental dredging after the pollution from external sources is effectively controlled in rivers, lakes and oceans. Environmental dredging refers to the overall planning and comprehensive consideration of general dredging activities and environmental protection contents such as soil care, ecological reconstruction, environmental improvement and resource utilization. By means of treatment, the pollution of internal sources of water can be removed and the ecological restoration condition of water environment can be created.

2. Technical requirements for environmental dredging

The purpose of environmental dredging is to remove the polluted sediment in oceans, lakes, rivers and other water bodies, strictly control the precision of dredging, and focus on the prevention and control of secondary pollution such as the rediffusion of polluted sediment during dredging and the leakage of polluted sediment during transportation.

Key technologies in the process of environmental dredging include dredging scale design, dredging measure of polluted sediment, accurate positioning of dredging space, residual water treatment after dredging, and storage and disposal of dredged sediment, etc.

 2.1 Choice of environmental dredging equipment

The choice of dredging equipment is directly related to the type and technology used: (1) Different dredging equipment has different disturbance degree to sediment, and the mechanism and characteristics of preventing diffusion and leakage are also different. Therefore, the pollution of dredging materials caused by different dredging equipment is different in the dredging process. (2) Generally, the control technology of environmental protection dredging equipment should be considered, because environmental dredging has high precision requirements for spatial positioning and depth control, the dredging section should be close to the bottom sediment pollution surface, otherwise, it will cause secondary pollution, and the over-excavation and leakage should be avoided and reduced as much as possible.

 2.2 Dredging technology

In the process of environmental dredging, a suitable storage site for contaminated sediment should be selected according to the requirements, and then the cleaned contaminated sediment should be transported to the selected location. Generally speaking, there is a certain distance between the pollutant storage yard and the construction area, which may cause secondary pollution along the process of transportation, which should be avoided as far as possible. Therefore, the key technology for the transportation of polluted sediment in the environmental protection dredging process is how to solve the secondary pollution problem in the dredging process.

 2.3 Treatment technology of polluted sediment

In the course of dredging construction, the polluted sediment removed from the coastal areas of rivers, lakes and oceans contains a large number of pollutants that may cause harm to the environment, which cannot be directly discharged into the water body of the outland reclamation or stored in the space of the land storage yard. Ecological risk assessment should be carried out for polluted sediment in strict accordance with relevant regulations. According to the requirements, appropriate treatment plans should be made for the pollution hazard and degree of sediment to avoid pollution and harm to the surrounding water and land environment.

3. Environmental characteristics of dredging projects

Due to different dredging purposes, environmental protection dredging has different engineering characteristics from conventional dredging, which is mainly used to dredge channels and increase storage capacity. Environmental dredging has many technical characteristics different from ordinary dredging because of the different purposes of the two dredging measures. The environmental protection dredging construction has the following characteristics: the dredging quantity is relatively small. The pollutant content in dredging sediment is high. The dredging boundary, dredging depth and elevation requirements are special and should be determined according to the distribution of pollutants and other conditions. Avoid diffusion during dredging. Dredged soil is relatively soft. Environmental dredging is generally non-repetitive.

These characteristics of environmental dredging determine that environmental protection dredging requires high precision, which needs to be carried out carefully, secondary pollution should be avoided as far as possible, and its impact on the environment should be positive. These technical characteristics of environmental dredging also pose challenges to dredging equipment and dredging technology.

4. The development of environmental dredging equipment

Up to now, the development of environmental dredging in China has only a decade of history and engineering experience. The research and application technology of the environmental underwater dredging equipment are still in the preliminary stage, and many technical means and methods have some defects and are not mature yet. At present, there is a big gap between the research and development of environmental protection dredging equipment and technology in China and the developed countries. At present, the research and development of environmental dredging equipment in the world can be summarized into two categories: First, the existing dredging equipment can meet the requirements of environmental dredging. Second, based on the concept of environmental protection, the special dredging equipment developed for environmental dredging. Relatively speaking, in the above two research and development methods of environmental dredging equipment, the transformation and upgrading of existing dredging vessels and dredging equipment with environmental protection functions are one of the most common and commonly used methods at present, and also the most economical and practical methods. At present, the transformation and upgrading of dredger mainly focus on dredging equipment and positioning control, that is to replace the original dredging equipment with a new environment-friendly reamer, and equipped with advanced high-precision positioning and monitoring system to reduce secondary pollution in the dredging process and meet the requirements of environmental dredging.

Compared with the traditional dredging equipment, the economic efficiency of the special environmental dredging equipment is poor due to the high production cost and the uniqueness of the environmental dredging project. In addition, in general, most of the special equipment for environmental dredging has low dredging capacity, which cannot meet the requirements of large-scale environmental dredging projects. Therefore, in the practical dredging engineering application, the special environmental protection dredging equipment is still rare. Since the beginning of the 21st century, China’s research and development institutions and other dredging groups began to actively develop environmental protection dredging equipment and has also achieved some remarkable results through research, and successfully applied in practical projects.

5. Conclusion

Although due to our increasing awareness of environmental protection, rivers, lakes, oceans and other waters have made great progress in the control of exogenous contamination and have been well controlled. However, after the external pollution is controlled, how to adopt effective environmental protection dredging engineering measures is the main problem that should be considered to solve the problem of internal pollution.