Analysis of common sludge disposal methods

      In the field of sludge disposal, the basic requirement for sludge disposal is that when the treated sludge is disposed in the natural environment (ground, underground, water) or reused, it can achieve long-term stability and has no adverse impact on the ecological environment. After years of exploration and practice in the field of sludge disposal, the main methods of sludge disposal in China are: Land landfill, landscaping, building materials, incineration power generation, etc.

1. Landfill. Land landfill is to dump the sludge directly into the lowland or valley after simple sterilization treatment. Because of the difficulty of site selection, it is almost impossible to build a special sludge landfill in China, and the capacity of China’s current landfill is very valuable. Therefore, as the main means of sludge disposal, sludge land landfill should be a long-term transitional measure, which should be used when other disposal methods cannot be realized.

      The main disadvantages of landfill disposal are: large land area; large amount of landfill leachate may cause land pollution due to the high content of organic matter in sludge; sludge has high fertilizer efficiency and calorific value, so landfill can not play its resource value, which will lead to waste of resources.

2. Landscaping. As a large agricultural country, China has a considerable gap in the use of organic fertilizers because of the flooding application of fertilizers, which makes the content of organic matter in the soil decrease year by year. Sludge, as a kind of organic matter rich substance, is widely used in landscape and land use. The advantage of sludge land use is that it does not need landfill volume. The resource-based substances in sludge can be effectively utilized, but there are environmental risks. The harmful substances in sludge may have adverse effects on groundwater, surrounding water and crops. In the specific use, there are mainly the following aspects:

(1) Sludge makes fertilizer. Through the biochemical degradation of the organic matter in the sludge, it can be transformed into stable humus and used as organic fertilizer.

(2) Soil improvement. The sludge after stabilization, sterilization and drying was used as soil improver.

(3) Fill soil for site leveling. In the process of urban municipal construction, a large amount of fill soil is needed for site leveling, so that the dried sludge can be used as the source of fill soil for part of the construction site.

3. Make building materials. Sludge with moisture content of more than 70% is rich in burning volatile substances such as organic matter. After firing, its capacity reduction rate is very large, and the remaining substances can be stably fixed in the bricks without adding other chemical additives. And because sludge is rich in organic matter and other combustibles, the combustion heat of the combustibles in sludge can be fully used in the process of brick firing to reduce the raw coal used for brick firing, which is a new direction of sludge disposal.
4. Incineration power generation. The water content of sludge is complex, including free water, gap water, surface water, combined water and other forms. The sludge after concentration and dehydration is dried to form a dry hard sludge with a water content of about 30%. When the heat value reaches 2000-2500 kcal / kg, it can form spontaneous combustion, maintain combustion, reduce the coal consumption of combustion furnace and save energy. If there are thermal power plants and other urban power supply and heating facilities around the urban area, the waste heat or thermal energy of these power plants can be used to dry the sludge, and the heat value of the dried sludge can be mixed with coal to generate electricity, so as to realize energy utilization. Incineration power generation is also the technological route of sludge treatment and disposal encouraged by China.

       Doyen China has analyzed the main ways of sludge disposal in China and their advantages and disadvantages. Through the above introduction of science and technology, we can see that sludge disposal has advantages and disadvantages. For China’s national conditions, it should not be limited to a certain disposal method, but should be comprehensively considered according to the nature and quantity of local sludge and other factors to choose the right method to adapt to the local development environment.

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