Why sludge incineration is only a transitional option？

     In April this year, the technical guidelines for sludge treatment and disposal in urban sewage treatment plants were promulgated. According to Dai Xiaohu, an expert involved in the compilation and review and director of the National Engineering Research Center for urban pollution control of Tongji University, the sludge incineration technology has reached a consensus at the level of ministries and commissions and some local governments, which is only a transitional and temporary technical policy. From the perspective of macro-control, the overall cost is still too high if all organic matter is burned off by sludge incineration.

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    From the perspective of future resources, one of the most scarce resources in the world is phosphate rock. According to calculation, the current global phosphate rock reserves can only be developed for about 100 years, which is higher than the shortage of energy resources. The importance of phosphorus resources has been emphasized in Europe since the 1990s, and the price of world phosphate fertilizer has increased by 4-6 times in recent five or six years. If the sludge is burned and used as building materials, the phosphorus in the sludge will be solidified into the building materials or buildings, which can not be extracted and used fully.

    Dai Xiaohu stressed that the energy utilization rate of sludge incineration power generation is low. At present, although many people think that sludge incineration can generate electricity for energy recovery, but from the cognition of sludge itself, converting the recovered heat energy into electrical energy is secondary energy utilization, and the energy utilization efficiency is only 20% – 30%. Therefore, the future direction of energy utilization is to convert sludge into other energy which is easier to transport and can be applied in many aspects.

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    Based on the above factors, Dai Xiaohu believes that the separate incineration technology of sludge should only be used as a temporary and transitional measure. Many local governments have gradually realized this point. In the future, sludge treatment and disposal will gradually return to the road of resource utilization.

Why is it difficult to realize sludge land use?

The heavy metal content of industrial wastewater exceeds the standard after entering municipal wastewater, which restricts the possibility of land use

There are some problems in sludge incineration disposal, but each technology has its advantages and disadvantages. What is the application of other sludge disposal methods in China and what are their advantages and disadvantages?

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     Dai Xiaohu pointed out that the application of sludge anaerobic digestion process in China is relatively small, the investment is relatively high, and the equipment relies on import. Among more than 2000 sewage treatment plants in China, about 60 have adopted anaerobic digestion process, but only 10-30 have been operated, and only 10 have achieved relatively good operation effect, such as Xiaohongmen sewage treatment plant in Beijing and Bailonggang sewage treatment plant in Shanghai. Generally speaking, due to the limitation of management, policy and equipment investment, anaerobic sludge digestion technology has not been well applied in China.

     Sludge aerobic composting is a process widely used in the world and in China. This treatment method has good stability, can kill pathogenic bacteria and parasitic eggs. After treatment, the moisture content of sludge is low, and the operation and management is simple. However, the bottleneck is the need for a large number of auxiliary materials, otherwise the odor can not be effectively controlled, which will increase the cost.

    Sludge landfill is a very simple treatment method, but it will bring a lot of leachate after treatment, including methane gas produced by organic matter. Therefore, many sludge landfills in our country have made solidification devices, which use lime to solidify and then landfill. In this way, the landfill cost is high, the land resources are occupied, and the useful and valuable materials in the sludge are not fully utilized. Dai Xiaohu, who has studied in Germany for many years, is very familiar with the development of the technical route of sludge treatment and disposal in Germany. He said that since 2005, Germany has required that the content of organic matter in all materials entering the landfill site should not exceed 5%, that is to say, the landfill technology route of sludge and organic kitchen waste has been banned in Germany, which is the first country in the European Union to do so.

    From the current trend, sludge land use is bound to be the future direction of development, organic matter in sludge can be added to the soil, and less energy consumption. However, according to the current situation in China, there are still many bottlenecks in land use. The main problem is industrial wastewater treatment. Although there are many strict standards for industrial wastewater treatment, some of the standards have poor operability, which leads to the illegal discharge of wastewater. The heavy metal content of these wastewater exceeds the standard after entering the municipal sewage, which further restricts the possibility of land use. Therefore, Dai Xiaohu suggested that during the 12th Five Year Plan period, the Ministry of environmental protection and the Ministry of construction should focus on regulating the supervision and treatment of industrial wastewater.

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