In recent years, urban living garbage continues to increase, environmental pollution problems are prominent, the direction of the development of garbage disposal and technical routes are increasingly concerned about, has become one of the most difficult problems facing the city government.
1 Analysis of the main problems
In 2003, the amount of domestic garbage removal in 660 cities in China amounted to 150 million tons, growing at a rate of about 4% per year. According to the statistics of the data reported by each place, the current rate of harmless treatment of urban domestic waste is about 51%. However, according to the survey and analysis of 388 domestic waste disposal sites (plants) in 255 cities, the standard rate of harmless treatment facilities for urban domestic waste in China is about 25%, and the actual rate of harmless treatment is less than 20%, taking into account factors such as operation and management. Garbage pollution of the environment, endangering the masses (especially farmers) is very prominent.
In recent years, the state has implemented a positive financial policy, urban waste disposal has been supported, a number of state bond projects have been built. At the same time, through the promotion of market-oriented reform, the diversification of the main pattern of investment began to take shape, urban waste disposal began to enter a period of rapid development. However, in general, the direction of development of municipal waste disposal is not clear, really suitable for the national conditions of the technical route has not been formed, some tendency problems have been revealed, and will likely affect the healthy development of the industry as a whole.
1.1 The proportion of landfill disposal is too large
Difficult to meet the requirements of sustainable development and circular economy. At present, the proportion of landfill disposal of waste is more than 85%, and the problem is also the most prominent. First, the consumption of large amounts of land resources, many cities are difficult to find new landfill sites; Second, the production of large amounts of leachate, most of the landfill leachate pollution problems; Third, the landfill gas pollution of the atmosphere, and the existence of safety hazards, and currently able to landfill gas resource utilization of landfill sites less than 3%; Fourth, most of the recyclable resources are buried, can not be regenerated and utilized. The survey also showed that the construction of standardized harmless landfill, investment is not as imaginative as saving. 1 day to deal with 1,000t of garbage landfill (20 a period of use, serving a population of about 1 million people), the need to invest 200-300 million yuan, per ton of garbage disposal costs (including investment costs) amounted to 60-80 yuan.
1.2 Incineration is developing rapidly
Some projects have hidden dangers and risks. Waste incineration for power generation is one of the main ways used in Europe, America and Japan. In recent years, China's waste incineration technology has been rapid development, there are about 50 domestic waste incineration plant into operation, nearly 100 waste incineration projects are under planning and construction, only Dongguan City plans to build more than 10 waste incineration plant. Waste incineration power generation in the waste reduction and heat utilization has certain advantages, however, in the process of development must be calmly analyzed some tendencies of the problem. First, high investment and operating costs. Daily treatment of 1,000t of garbage project investment of 400 million -600 million yuan, the average cost per ton of garbage treatment more than 1SO yuan; Secondly, it is dependent on higher feed-in tariffs. The feed-in tariff for coal-fired thermal power generation is about $0.3 per kWh, while the feed-in tariff for waste-to-energy generation generally exceeds $0.5. In order to chase power generation revenue, some enterprises add excessive coal, actually evolved into a "small thermal power" project; Third, incineration of fly ash is not properly disposed of. In accordance with environmental requirements, fly ash because it contains excessive amounts of toxic and hazardous substances, should be disposed of according to hazardous waste, the disposal cost of up to 1 S00 yuan / t or so, that is, the cost of disposal of each ton of garbage should be increased by tens of dollars to hundreds of dollars. This cost is mostly ignored. In addition, the problem of dioxin pollution from garbage incineration remains a focus of concern for all sectors of society. China's domestic waste has a low calorific value, about 1/3 of that of developed countries, and is not suitable for incineration. Garbage plus coal incineration is a desperate move, the thermal utilization efficiency of coal is about 1/2 of the conventional boiler coal combustion, in terms of technical and economic aspects of whether it is reasonable to be further studied.
1.3 Biological composting technology is a mixed bag
A number of national bond projects into the "garbage project". The use of domestic waste composting in our country for a long period of time, but the effect is not good. The prominent problem is that the garbage sorting efficiency is low, poor quality fertilizer, there is no market sales. Recently investigated and dealt with in Sichuan, Anhui, a number of garbage disposal projects, the vast majority of mechanical sorting and biological composting technology, can not operate normally. The main reason, one is that some departments of decision-making mistakes, poor supervision; second is the design of the wrong ideas, immature technology, equipment, crude or blindly introduced.
2 Adjustment of Ideas
2.1 Re-understanding of the characteristics of domestic waste
The main characteristics of domestic waste in China are different from those of developed countries. Firstly, the water content of domestic waste in China is high, generally 55%-65%, and as high as 70% in summer in some southern cities, while it is generally 30%-35% in western countries. Secondly, the proportion of organic waste such as food waste and catering in China's domestic waste is large, 45%-55%, while it is generally around 20% in western developed countries. Thirdly, China's domestic waste is still mainly collected in a mixed way, despite the vigorous implementation of separate collection of domestic waste in recent years, but with little effect. The vast majority of cities across the country deal with mixed primary waste. The rate of separate collection of domestic waste in developed countries is more than 60%, and more than 80% in some European countries such as Germany.
These characteristics of domestic waste in China make the problems we face more difficult than those in developed countries. First, the landfill leachate produced by a large amount of high concentration of pollutants; the second is the low calorific value of domestic waste, most of which is not suitable for direct incineration; the third is the mixed garbage has a "sticky" nature, it is difficult to carry out mechanized sorting, resource recovery rate is low, the quality of composting is poor. Over the years, we pay great attention to learn from or introduce foreign technology and equipment, but practice shows that foreign technology and equipment in our country is not fully applicable. It is imperative to further recognize the characteristics and impact of domestic waste in China, strengthen targeted research and practice, and develop technologies and equipment suitable for national conditions.
2.2 Reflection on the technical route
Over the years, our technological research and capital investment have focused on two aspects, one is to carry out the necessary modification and localization on the basis of the introduction of foreign technology and equipment to make them suitable for China's garbage treatment; and the other is to strengthen the treatment of end-end pollution to meet the requirements of environmental standards.
In the landfill treatment, in order to prevent leachate pollution of groundwater, we have adopted the internationally popular artificial seepage control measures, such as the Three Gorges Reservoir area of those poor areas, but also the widespread use of geotextile and high-density membrane seepage control structure; in order to purify the leachate, some areas to introduce the expensive "reverse osmosis" technology and equipment, treatment of each ton of sewage investment of nearly 10 million yuan. Treatment of each ton of sewage investment of nearly 100,000 yuan, the operating cost of tens of dollars. In incineration, we have studied for many years the adaptability of low calorific waste, but it is impossible to change some of the basic laws of combustion science, combustion efficiency and high cost is difficult to avoid; due to the complexity of the composition of mixed garbage, incineration pollution is serious, and is currently adopting the international advanced management technology, flue gas treatment of the investment is almost the same as the main body of the incineration. In biological composting, some cities introduced the United States, Germany and other mechanical equipment, but still can not solve the problem of sorting of domestic waste.
Borrowing from foreign experience and strengthen pollution control, in principle, are correct, but in the face of problems in practice, to reflect on: one is to let foreign technology to adapt to China's garbage, or make China's garbage to adapt to these technologies? The second is to emphasize the end of the pollution treatment, or from the source to control and reduce the generation of pollution? On the basis of investigation and research, scientific tests and engineering practice, we put forward proposals to adjust the technical route:
Firstly, most of the municipal garbage is suitable for biological pretreatment, focusing on cutting the water and organic matter in the garbage, improving the characteristics of the garbage, and creating the conditions for the subsequent treatment and reduction of pollutants; secondly, to strengthen the mechanical sorting of garbage and improve the efficiency of sorting and classification of Kunhe garbage. Kunhe garbage sorting and classification efficiency; third, the rational choice of classification and disposal technology, complementary advantages; fourth, the prudent development of mixed garbage incineration technology, to strengthen the comprehensive assessment of technology and economy; fifth, to limit the mixed garbage direct landfill, the source of control of pollution, reduce land consumption.
2.3 Resource Recycling
It is generally believed that China's huge "scavenging army" has basically solved the problem of resource recycling in garbage, and in the final treatment process, few wastes can be directly recycled, and resources are mainly utilized through incineration for power generation. However, surveys have shown that in the final treatment of domestic waste, more than 20% of the waste can be directly recycled, of which plastics and rubber accounted for 6%-9%, paper 4%-6%, including a certain amount of fabrics, metal and glass, etc.. These recyclable materials a burn, not only low utilization efficiency, but also cause serious smoke pollution. Practice has proved that, as long as the solution of mechanical sorting and screening technology, the vast majority of the available resources in the garbage can be directly recycled, and at the same time can produce about 8% of the total amount of high-quality base fertilizer, can be used first for urban greening and forestry. China is a resource-poor country, should vigorously develop the circular economy, focusing on the direct recycling of waste resources, and focus on the development of domestic waste disposal as a resource recycling industry.
3 Demonstration project inspiration
Since 1996, the American International Group (hereinafter referred to as "American") visited more than 200 cities in China, and carried out in-depth research on the characteristics of domestic garbage. 1998 "American" construction in Daqing City. "In 1998, AmCham built the first integrated waste treatment plant in Daqing, which also experienced a series of setbacks (the equipment imported from the U.S. was turned into a pile of scrap metal), but began to explore treatment ideas and processes suitable for the characteristics of China's domestic garbage. 2002, the Pudong New Area of Shanghai, after a number of inspections and rigorous validation, decided to invest in the construction of a comprehensive garbage treatment plant by AmCham. "In May 2003, the project was completed and put into trial operation. The new idea and market-oriented operation of the project attracted great attention from the Ministry of Construction, which sent people to carry out research 8 times and organized experts to follow up the investigation. 2004 February, the Department of Urban Construction of the Ministry of Construction held an on-site meeting to further investigate and discuss the matter, and the experts evaluated that: the project is based on the characteristics of China's garbage, and adopts a comprehensive treatment technology route, which fully embodies the principles of "reduction, resource utilization, and harmlessness",
The project was included in the Science and Technology Demonstration Project of the Ministry of Construction in April 2004, which provided practical experience in large-scale projects and was of great significance for reference.
The main features and benefits of this project are summarized as follows:
3.1 Highly efficient biological pretreatment technology.
Through bin aerobic fermentation, the reduction of moisture and organic matter of garbage is realized firstly. Moisture is reduced from 60%-80% to about 35%, volatile organic matter is degraded by about 50%, and total mass is reduced by about 40%. The garbage characteristics are improved for mechanical sorting and subsequent processing.
3.2 Advanced mechanical sorting equipment.
A full set of localized equipment, the recovery rate of usable resources in the garbage is more than 90%, including plastics, paper, metal, glass, batteries, lighters and so on. At the same time, automatic classification of garbage is realized.
3.3 Applicable classification and disposal technology.
Secondary fermentation of organic matter, refined composting, generating about 8% of the total amount of garbage; incineration of bamboo, wood, paper and textile, heat utilization; landfill of residues, maximizing the reduction (no more than 20% of the total amount of garbage).
3.4 Reasonable "three wastes" management.
The water of garbage is mainly removed by water and gas evaporation, and a small amount of leachate is used back to the second composting and fermentation; organic matter is composted through biochemical composting, turning harm into benefit; incineration is based on "firewood", and the flue gas pollution is reduced; the residue landfill is as much as possible reduced, inorganic, and low-water, and pollutants are cut at the source; and biological deodorization technology is used to effectively control air pollution.
As a market-oriented operation project, the "U.S." construction investment of nearly 200 million yuan, and bear all the operational responsibilities and costs. In accordance with the franchise agreement, the Shanghai Pudong environmental health management department stationed supervisors for the whole process of supervision, the government pays 50 yuan per ton of garbage disposal fee. This cost, equivalent to 1/4 of incineration, even lower than the cost of landfill disposal. Of course, investors also have their own profit model, it is understood that, through the sale of "waste" per ton of garbage can earn more than 30 yuan, per ton of organic fertilizer can also be sold for about 200 yuan.
"American" demonstration project gives us an important revelation: First, "reduce, resource, harmless" model of waste disposal can be achieved; Second, the government and the enterprise win-win market mechanism can be established.
4 Suggested Measures
4.1 Strengthen scientific research on waste pretreatment technology.
Through biological pretreatment, the realization of water and organic matter reduction and the improvement of the characteristics of domestic garbage will likely have a positive impact on the subsequent incineration, landfill and so on. According to our preliminary test on Beijing Shunyi waste incineration plant, domestic waste after simple biological fermentation and screening, the volume reduction is nearly 50%, and the heat generation is increased by about 2.5 times, which has significant technical and economic benefits.
4.2 Increase the development of waste sorting equipment.
"U.S." experience proves that biological pretreatment will create favorable conditions for mechanical sorting, while targeted improvement of the performance of sorting equipment is also critical. It is recommended that the state arrange appropriate support funds to support the research and development of domestic sorting equipment to further improve the efficiency of resource recovery. At the same time, to strengthen the "waste" processing and utilization of supervision and management, through the development of standardized, large-scale resource recycling industry, and gradually solve the "army of scavengers" problem.
4.3 Encourage the use of recycled organic fertilizer.
City governments should formulate policies to encourage the priority use of compost that meets standards in urban greening and forestry, and gradually reduce the use of chemical fertilizers.
4.4 Adjust and improve the technical policy on the basis of practical verification.
Advocating biological pre-treatment of domestic garbage, focusing on cutting water and organic matter in garbage, creating conditions for subsequent treatment and reducing pollution; strengthening mechanical sorting of garbage, improving the efficiency of sorting and classifying mixed garbage; reasonably choosing classification and disposal technology, vigorously developing garbage treatment resource regeneration industry, gradually restricting mixed garbage from going directly to landfills, focusing on controlling pollution at the source, and reducing the land resource
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