In recent years, the municipal solid waste is increasing, and the problem of environmental pollution is outstanding. More and more attention has been paid to the development direction and technical route of municipal solid waste treatment, which has become one of the biggest problems faced by the city government.
Analysis of main problems of 1
In 2003, the domestic garbage removal in 660 cities nationwide reached 654.38+0.5 billion t, with an annual growth rate of about 4%. According to the statistical data reported by various places, the current harmless treatment rate of municipal solid waste is about 5 1%. However, according to the investigation and analysis of 388 domestic waste treatment plants (factories) in 255 cities, the compliance rate of domestic waste harmless treatment facilities in China is about 25%, and the actual harmless treatment rate is less than 20% considering factors such as operation management. The problem that garbage pollutes the environment and harms people (especially farmers) is very prominent.
In recent years, the state has implemented a proactive fiscal policy, and urban garbage disposal has been supported, and a number of national debt projects have been built one after another. At the same time, by promoting market-oriented reform, the diversified pattern of investment subjects began to take shape, and the treatment of municipal solid waste began to enter a period of rapid development. But on the whole, the development direction of municipal solid waste treatment is not clear, the technical route that really suits the national conditions has not yet been formed, and some tendentious problems have appeared, which may affect the healthy development of the whole industry.
1. 1 The proportion of landfill treatment is too large.
It is difficult to meet the requirements of sustainable development and circular economy. At present, the proportion of landfill disposal exceeds 85%, and the problem is also the most prominent. First, it consumes a lot of land resources, and it is difficult for many cities to find new landfills; Second, a large amount of leachate is produced, and most garbage dumps have leachate pollution problems; Third, landfill gas pollutes the atmosphere and has potential safety hazards. At present, less than 3% of landfills can recycle landfill gas. Fourth, most recyclable resources cannot be recycled once they are buried. The survey also shows that the investment in the construction of standardized and harmless landfills is not as economical as expected. 1 daily garbage disposal capacity of landfill site 1 000t (the service life is 20 years, and the service population is about 1 10,000 people) requires an investment of 200-300 million yuan, and the garbage disposal cost per ton (including investment cost) reaches 60-80 yuan.
1.2 incineration has developed rapidly.
Some projects have hidden dangers and risks. Waste incineration for power generation is one of the main ways adopted by European and American countries and Japan. In recent years, China's waste incineration technology has developed rapidly. At present, about 50 domestic waste incineration plants have been put into operation, and nearly 100 waste incineration projects are under planning and construction. Dongguan alone plans to build more than 65,438+00 waste incineration plants. Waste incineration power generation has certain advantages in waste reduction and heat energy utilization, but some tendentious problems must be calmly analyzed in the development process. First, the investment and operating costs are high. 1 000t daily investment of garbage disposal project is 400-600 million yuan, and the average cost of garbage disposal per ton exceeds 1SO yuan; The second is to rely on higher on-grid tariffs. The on-grid price of coal-fired thermal power generation is about 0.3 yuan per kWh, while that of garbage power generation generally exceeds that of 0.5 yuan. In order to chase the power generation income, some enterprises added too much coal and actually evolved into "small thermal power" projects; Third, the fly ash generated by incineration has not been properly disposed of. According to the requirements of environmental protection, fly ash should be treated as hazardous waste because it contains excessive toxic and harmful substances, and the disposal cost is as high as 1 S00 yuan /t, that is, the disposal cost per ton of garbage will increase by tens to hundreds of yuan. This cost is largely ignored. In addition, dioxin pollution caused by garbage incineration is still the focus of attention from all walks of life. The calorific value of domestic waste in China is low, about 1/3 of that of developed countries, so it is not suitable for incineration. Burning garbage with coal is a helpless move. The heat utilization rate of coal is about 1/2 of that of ordinary boilers. Whether it is reasonable in technology and economy needs further study.
1.3 biological composting technology mixing.
A number of national debt projects have become "junk projects". Domestic waste compost has been used in China for a long time, but the effect is not good. The outstanding problems are low garbage sorting efficiency, poor fertilizer quality and no market. Recently, a number of garbage disposal projects in Sichuan, Anhui and other places have been investigated, and most of them adopt mechanical sorting and biological composting technology, which can not operate normally. The main reasons are: First, some departments make mistakes in decision-making and lack supervision; Second, the design idea is wrong, the technology is immature, the equipment is shoddy or blindly introduced.
2 the adjustment of ideas
2. 1 Re-understanding of the characteristics of domestic waste
The main features of domestic waste in China are different from those in developed countries. First, the water content of domestic waste in China is high, generally 55%-65%, and it is as high as 70% in some cities in the south in summer, while it is generally 30%-35% in western countries. Second, the proportion of kitchen waste, catering and other organic waste in domestic waste in China is relatively large, which is 45%-55%, and it is generally around 20% in western developed countries. Third, China's domestic waste is still mainly mixed collection. Although the classified collection of domestic waste has been vigorously promoted in recent years, it has achieved little effect. Most cities in China deal with mixed primary garbage. However, the classified collection rate of domestic waste in developed countries is over 60%, and that in some European countries such as Germany is over 80%.
These characteristics of domestic waste in China make the problems we face more difficult than those in developed countries. First, the amount of leachate produced by landfill is large and the concentration of pollutants is high; Second, the calorific value of domestic waste is low, and most of it is not suitable for direct incineration; Third, the mixed garbage is "sticky", which is difficult to separate mechanically, with low resource recovery rate and poor compost quality. Over the years, we have attached great importance to learning or introducing foreign technology and equipment, but practice shows that foreign technology and equipment are not fully applicable in China. The urgent task is to further understand the characteristics and influence of domestic waste in China, strengthen targeted research and practice, and develop technologies and equipment suitable for the national conditions.
2.2 Thinking about the technical route
Over the years, our technical research and capital investment have mainly focused on two aspects. First, on the basis of introducing foreign technology and equipment, make necessary transformation and localization to make it suitable for garbage disposal in China; The second is to strengthen the end pollution control and meet the requirements of environmental protection standards.
In landfill treatment, in order to prevent leachate from polluting groundwater, we have adopted internationally popular artificial anti-seepage measures, such as the high-density membrane geotextile anti-seepage structure adopted in those poor areas in the Three Gorges reservoir area. In order to purify leachate, some areas have introduced expensive "reverse osmosis" technology and equipment, with an investment of nearly 654.38+million yuan per ton of sewage treatment and operating costs of several tens of yuan. In the aspect of incineration, we have studied the adaptability of low calorific value garbage for many years, but some basic laws of combustion science cannot be changed, and low efficiency and high cost of combustion are inevitable; Due to the complex composition of mixed domestic waste and serious incineration pollution, the international advanced treatment technology has been adopted at present, and the investment in flue gas treatment is almost equal to that of incineration main body. In terms of bio-composting, some cities have imported machinery and equipment from the United States and Germany, but they still can't solve the classification problem of domestic waste.
It is correct in principle to learn from foreign experience and strengthen pollution control, but in the face of practical problems, we should reflect: first, should foreign technologies adapt to China's garbage or China's garbage adapt to these technologies? Second, blindly emphasize the end treatment of pollution, or control and reduce pollution from the source? On the basis of investigation, scientific experiment and engineering practice, we put forward suggestions for adjusting the technical route:
First of all, most of the municipal solid waste is suitable for biological pretreatment, and the key point is to reduce the moisture and organic matter in the waste, improve the characteristics of the waste, and create conditions for subsequent treatment and reduction of pollutants; Second, strengthen the mechanical separation of garbage, improve? Kunming garbage classification and classification efficiency; Third, the reasonable choice of classified disposal technology, complementary advantages; Fourth, prudently develop mixed waste incineration technology and strengthen comprehensive evaluation of technology and economy; Fifth, limit the direct landfill of mixed garbage, control pollution from the source and reduce land consumption.
2.3 About resource recovery
It is generally believed that the huge army of scavengers in China has basically solved the problem of recycling resources in garbage. In the final treatment process, few wastes can be directly recovered, and resources are mainly utilized through incineration and power generation. However, the survey shows that in the final treatment of domestic waste, more than 20% of the waste can be directly recycled, including 6%-9% of plastic and rubber, 4%-6% of paper, and a certain amount of fabric, metal and glass. Once these recyclable materials are burned, they not only have low utilization efficiency, but also cause serious smoke pollution. Practice has proved that as long as the mechanical sorting and screening technology is solved, most of the available resources in garbage can be directly recovered, and at the same time, high-quality base fertilizer accounting for about 8% of the total garbage can be produced, which can be used for urban greening and forestry at first. China is a country lacking in resources, so we should vigorously develop circular economy, pay attention to the direct recycling of garbage resources, and strive to develop domestic garbage treatment into a resource recycling industry.
3 Enlightenment of demonstration project
Since 1996, China Merchants International Group (hereinafter referred to as "American Merchants") has visited more than 200 cities in China and conducted in-depth research on the characteristics of domestic waste. From 65438 to 0998, "American Merchants" built the first comprehensive garbage treatment plant in Daqing City, and experienced a series of setbacks (the equipment imported from the United States turned into a pile of scrap iron), but began to explore the treatment ideas and processes suitable for the characteristics of domestic garbage in China. In 2002, after many investigations and strict argumentation, Shanghai Pudong New Area decided to build a comprehensive garbage treatment plant with a daily capacity of 1000 tons. In May 2003, the project was completed and put into trial operation. The new ideas and market-oriented operation mode of the project have aroused great concern of the Ministry of Construction, and sent people to conduct research for 8 times and organized experts to follow up the investigation. In February, 2004, the Urban Construction Department of the Ministry of Construction held a site meeting for further investigation and discussion. According to experts' evaluation, according to the characteristics of China's garbage, the project has adopted a comprehensive treatment technical route, which fully embodies the principle of "reduction, recycling and harmlessness" and provides practical experience for large-scale projects, which has important reference significance. In April, 2004, the project was included in the science and technology demonstration project of the Ministry of Construction.
The main features and advantages of this project are summarized as follows:
3. 1 Efficient biological pretreatment technology.
Through aerobic fermentation in silo, the reduction of moisture and organic matter in garbage was realized at first. The water content is reduced from 60%-80% to about 35%, the volatile organic compounds are degraded by about 50%, and the total mass is reduced by about 40%. The characteristics of garbage are improved, which is beneficial to mechanical separation and subsequent treatment.
3.2 Advanced mechanical sorting equipment.
The whole set of domestic equipment, the recovery rate of available resources in garbage exceeds 90%, including plastics, paper, metal, glass, batteries, lighters and so on. At the same time, realize the automatic classification of garbage.
3.3 Applicable classified disposal technology.
The garbage produced by secondary fermentation and fine composting of organic matter accounts for about 8% of the total garbage; Combustion of bamboo, wood, paper and textiles, and utilization of heat energy; Landfill the residue and minimize it (no more than 20% of the total garbage).
3.4 Reasonable treatment methods of "three wastes".
The moisture of garbage is mainly removed by steam evaporation, and a small amount of leachate is reused for secondary composting fermentation; Organic matter turns harm into benefit through biochemical composting; Incineration is mainly based on "firewood", and smoke pollution is reduced; Waste residue landfill should be minimized, inorganic, low water differentiation, and reduce pollutants from the source; Adopt biological deodorization technology to effectively control air pollution.
As a market-oriented operation project, "American Business" has a construction investment of nearly 200 million yuan, and bears all operational responsibilities and expenses. According to the franchise agreement, Shanghai Pudong Environmental Sanitation Management Department sent supervisors to supervise the whole process, and the government paid the garbage disposal fee per ton of 50 yuan. This cost is equivalent to 1/4 of incineration, even lower than that of landfill. Of course, investors also have their own profit model. It is understood that by selling "waste products", they can earn more than 30 yuan per ton of garbage, and each ton of organic base fertilizer can also be sold around 200 yuan.
The "American Business" demonstration project has given us important enlightenment: First, it can realize the garbage disposal mode of "reduction, recycling and harmlessness"; Second, a win-win market mechanism can be established between the government and enterprises.
4 recommended measures
4. 1 Strengthen scientific research on waste pretreatment technology.
Through biological pretreatment, water and organic matter can be reduced, and the characteristics of domestic waste can be improved, which may have a positive impact on subsequent incineration and landfill. According to our preliminary test of Beijing Shunyi Waste Incineration Plant, after simple biological fermentation and screening, the amount of domestic waste is reduced by nearly 50%, and the calorific value is increased by about 2.5 times, which has remarkable technical and economic benefits.
4.2 Strengthen the development of garbage sorting equipment.
The experience of "American Business" proves that biological pretreatment will create favorable conditions for mechanical separation, and it is also very important to improve the performance of separation equipment. It is suggested that the state arrange appropriate support funds to support the research and development of domestic sorting equipment and further improve the efficiency of resource recovery. At the same time, it is necessary to strengthen the supervision and management of the processing and utilization of "waste products" and gradually solve the problem of "the army of scavengers" by developing standardized and large-scale resource recycling industries.
4.3 Encourage the use of recycled organic fertilizer.
The city government should formulate policies to encourage the priority use of garbage compost in urban greening and forestry, and gradually reduce the use of chemical fertilizers.
4.4 On the basis of practice verification, adjust and improve the technical policy.
Advocate biological pretreatment of domestic waste, focus on reducing moisture and organic matter in waste, create conditions for subsequent treatment and reduce pollution; Strengthen the mechanical sorting of garbage and improve the sorting efficiency of mixed garbage; Reasonable selection of classified disposal technology, vigorously develop the recycling industry of garbage disposal resources, gradually limit the direct landfill of mixed garbage, pay attention to pollution source control, and reduce the consumption of land resources.
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