River has many advantages, such as flood control, drainage. However, in the course of river flow, there will be sediment deposition, not only raising the bed but also the long-term accumulation of silt that will cause eutrophication. This paper starts from the common difficulties of the river dredging project and then analyzes the methods of silt treatment, so as to provide relevant references for urban river dredging project and silt treatment.

River course plays a more and more important role in urban economic construction and development, which will inevitably result in the siltation of river course, bad dredging project, and increase eutrophication of the water body. Therefore, the quality of the river dredging project is related to the practical application effect of river dredging and the treatment measures of the mud generated in the dredging project are particularly important. A series of technical dredging methods must be taken to remove the dredging silt at the bottom of the river and properly dispose of the silt to improve water quality and enhance flood control and drainage capacity.

1.Common difficulties in river dredging

 1.1 Influence of construction back silting condition

Back-silting is the most difficult problem we often encounter in the course of river dredging construction, and the amount of back-silting is also the key to restrict the construction quality, which requires us to control the back-silting quantity within a certain threshold as much as possible. If the flow of the channel is large or the sedimentation rate is fast, the whole project may not be carried out and even the basic riverbed structure may be damaged.

 1.2 Influence of different bed layers

The riverbed is not all soil layer, construction often encounters special riverbed soil layer, such as clay layer and soft rock layer, etc. The construction of different bed layers is quite different. For example, the ordinary sediment bed contains special bed layers, which will reduce construction efficiency or even prevent construction and negatively affect the construction progress. Therefore, the change of soil layer should be paid attention to at any time in the excavation process. The depth of each excavation and installation should be determined to ensure the safety of dredging engineers and dredging equipment.

 1.3 Negative effects of hydro-meteorological conditions

River dredging projects are operated on water and are easily affected by hydro-meteorological conditions, which are mostly negative. Hydrological conditions are reflected by the river’s flow rate, flow direction, water level change, etc. While meteorological conditions are mainly reflected by wind, precipitation, etc., all of which are force majeure factors and will bring difficulties to the construction. For example, in areas where the water flow is relatively rapid, the water level changes rapidly, which deepens the difficulty of excavation depth control.

2.Treatment of silt in dredging works

 2.1 Sludge treatment in ecological dredging

Silt occurs in the course of river course operation and blocks the river course, and the silt generated has high water content, low hardness and deposition for a long time to form a large number of toxic and harmful substances, which must be treated effectively to avoid secondary pollution to the environment. The traditional way of dredging rivers is to dig up the silt and pile it on the empty land, which is relatively simple but will have a negative impact on the urban environment. Way at present, we are exposed to the dredging of river silt that exists in the first name, mixing with a different particle size of sludge and elutriation after separation. Then using physical methods for sludge dewatering and drying to moisture content is below 30%, so as to achieve the goal of slud to recycle. Environmental dredging is a sustainable economic means, which plays a positive role in promoting the optimal allocation of various resources.

 2.2 Measures to treat sludge in the process of resource utilization

The sludge treatment measures in dredging projects are generally divided into polluted sludge treatment and pollution-free sludge treatment according to the properties of sludge. After classification, the sludge will be transported to the storage yard for turnover, and the surface treatment of the silt will be dried quickly. If the pollutant exceeds the standard, the pollutant content must be reduced first, and the treated sludge will be used for filling soil or berm. If there is no heavy metal pollution, the storage yard can be recycled and used as soon as possible. At present, the specific situation of dredging silt in various areas of the country is not the same, combined with the current environmental protection policy, in line with the principle of resource utilization, the use of silt treatment measures mainly as garden green fertilizer, energy utilization and fill soil embankment.

2.2.1 Garden green fertilizer

Environmental dredging sediment fertilizer has made certain achievements in foreign countries, urban river dredging construction after the formation of the high content of organic matter, nutrient-rich organic fertilizer through the technical improvement of sludge compost. After the sludge drying and deodorization treatment, the moisture content is low, small volume, facilitate transportation and processing of goods used in farmland and green manure. It can also be used as fertilizer for the green belt along the river, providing organic fertilizer for the landscape along the river, saving freight, and achieving economic and social benefits.

2.2.2 Energy utilization

Sludge energy utilization technology is often adopted by many developed countries in the world, including incineration and utilization, production of building materials and so on. Sludge incineration process can kill pathogenic bacteria and organic pollutants, but the high cost and large energy consumption will also discharge pollutants exceed the standard of smoke, so we usually do not use this method. Commonly, “mud energy utilization” refers to the production of building materials, such as cement, brick, and ceramicist. In addition, a small amount of industrial waste, such as slag and construction waste can be added to the sludge with the addition of coagulant for unburned bricks. It is a kind of mud treatment method with relatively mature technology and obvious economic benefit.

2.2.3 The filled soil dike dam

The water content of sludge can be reduced by sludge drying technology, the drying technology to join curing material make it become the general degree of soil so that we can set biochemical sludge resources and silt but due to the nature, characteristics and the influence of the adding amount of curing material. The filling effect of silt is general and sludge solidification processing cost is high thus limiting the promotion.

3.Conclusion

Above all, the purpose of the river dredging project is unblocked and improved exhaust port of flood control and water quality. Due to the narrow channel and garbage pollutants, the dredged water must be surveyed in all directions and must choose the right means of dredging. Dealing with the silt generated in the dredging process is especially important. The utilization value of sludge treatment products should be continuously developed to improve the recycling of resources. Considering the environmental health and safety, secondary pollution, long-term economic benefits and other aspects, the practical sludge treatment measures are selected to reduce the cost and develop the available value of silt.