At present, domestic and foreign widely used municipal domestic waste treatment methods are mainly sanitary landfill, composting, incineration, fermentation biogas production method. 2008 statistics show that developed countries to deal with domestic waste disposal methods to incineration-based, Japan, Singapore, France, Belgium, Germany, the Netherlands, Switzerland, Denmark, Sweden, and other countries adopted incineration The proportion of incineration is 79%, 41%, 32%, 36%, 35%, 39%, 59%, 54%, 49%, and the landfill method is the main method in China, and the proportion of landfill method, incineration, and composting method is 81%, 14%, and 3% respectively.
In recent years, land resources are increasingly tight, the calorific value of waste gradually improved, the proportion of domestic incineration method is on the rise, composting is in a state of atrophy, the number of sanitary landfill disposal sites and processing capacity is in a state of growth. Recent statistics from China's Ministry of Housing and Urban-Rural Development (MOHURD) introduce that: as of September 2010, 849 non-hazardous treatment facilities for domestic waste have been built in cities, counties and some towns*** across the country, including 676 sanitary landfills, 90 composting plants, 90 incineration plants, and 76 comprehensive treatment plants. Harmless treatment capacity of 399,702 tons / day, of which 281,927 tons / day sanitary landfill, composting 1950 tons / day, incineration 68,865 tons / day, 46,960 tons / day of comprehensive treatment, sanitary landfill, incineration, composting capacity accounted for the proportion of about 70.5%, 17.2%, 0.5%, respectively.
1.1 Sanitary landfill method
Sanitary landfill is a widely used waste treatment technology at home and abroad, and is also an essential waste final disposal technology (Wang Wei, 2008). The United States because of the large land area, landfill method is lower than the cost of incineration method and the main use of landfill method to deal with waste, landfill accounted for 50% of the proportion of waste disposal; the British soil structure of the natural soil layer of 20 to 30m, has a good seepage capacity, more suitable for landfill, so the more common use of landfill process, landfill accounted for 55% of the proportion of landfill; China's landfill accounted for 81% of the proportion of the landfill.
- 84 -
1.1.1 The current state of the art of landfill method
Landfill treatment buries garbage into the ground, and through the long-term decomposition of microorganisms, it is decomposed into harmless compounds, and the treatment technology is mature, simple in operation and management, with a large treatment capacity and low operating costs, and is capable of treating and disposing of all kinds of wastes and can be utilized to generate electricity from landfill gas to provide the city with Electricity or heat energy to the city.
At present, most of the modern large-scale sanitary landfill of domestic waste in foreign countries use the unit landfill method, and compaction of waste in layers and daily cover, landfill impermeable treatment of synthetic materials as a liner, through the collection of landfill methane pipe and make it safe to direct combustion or through the pipeline system after the collection of evolutionary treatment as an energy source for recycling. China's domestic waste landfills can be divided into three categories: simple landfills; controlled landfills; sanitary landfills, and the number of sanitary landfills constructed and operated in strict accordance with standards is relatively small. Most of them adopt anaerobic landfill method in China. 1.1.2 Problems of landfill method
In today's increasingly rapid development of urbanization, landfill site selection is becoming more and more difficult, sanitary landfill treatment takes up a large amount of land resources, the landfill occupies a very long time, is not conducive to the reuse of land resources, and the process of waste landfill will produce a large amount of leachate, landfill gas and garbage floating dust, causing pollution to the environment.
1.2 Incineration method
Because of the advantages of incineration method of large treatment capacity, speed and small footprint, it is an effective way of treatment for domestic waste to achieve reduction, harmlessness and resource utilization. At present, Japan, Switzerland, Belgium, Denmark, France, Luxembourg, Sweden, Singapore and other countries have adopted the proportion of incineration, has been close to or exceeded the landfill. Waste incineration has also become an important direction of waste treatment in China. However, due to the complexity of the composition of domestic waste in China, the lack of effective classification and collection, and the calorific value is not high, although the development of waste incineration power generation has been relatively fast in recent years, the total proportion is still low, mainly concentrated in the eastern coast of the developed areas. 1.2.1 The technical status quo of incineration method
Incineration is a high-temperature thermochemical treatment of municipal household garbage, turning it into a process of inorganic ash, at a high temperature of about 800 to 1,000 degrees Celsius, the combustible components of household garbage and the oxygen in the air under the high-temperature conditions of a violent chemical reaction, in the process of the release of energy, to obtain high-temperature combustion gases and a small amount of stable nature of the solid Residue. The high-temperature gas produced by waste incineration can be recycled as heat energy, and the stable residue obtained from incineration can be directly used for sanitary landfill. This method has obvious effect of volume reduction, and the volume can be reduced by 80% to 90% after incineration. Occupies an area of small, flexible site selection, can be built in urban areas, saving the cost of garbage transportation.
Foreign incineration technology development has been relatively mature, the type of mechanical grate incinerator has matured, at present, the United States, Germany, Japan and other developed countries have carried out the domestic waste gasification melting technology research. China's waste incineration treatment technology mainly includes grate furnace technology and fluidized bed technology, of which the proportion of grate furnace technology is larger, mainly the introduction of foreign technology, while the fluidized bed technology is mainly dominated by domesticated technology. 1.2.2 Problems of incineration method
The most important problem faced by waste incineration is the generation of waste incineration exhaust gas, which contains a variety of pollutants such as particulate matter, SO2, SO3, NOX, HCl, HF, heavy metals, dioxin, etc., of which the most concerned and controversial is dioxin. Especially in China, domestic waste has high moisture and ash content, low calorific value, and requires more auxiliary fuels, and except for a few more economically developed cities, the mixed waste in other cities has lower calorific value and higher slag content, and the incineration fly ash has not been disposed of safely (Zhao Shucheng, et al., 2011).
Therefore, in recent years, the construction of domestic domestic waste incineration plants had been questioned.
1.3 Composting method
At present, the treatment rate of composting method at home and abroad is gradually declining, and although China has a long history of traditional composting technology, the rate of composting treatment is not high due to the fact that the classification of waste in China is not effectively implemented. 1.3.1 The technical status quo of composting method
Composting method is the use of nature's microorganisms to degrade the organic matter in the garbage, so that it becomes stable humus, which can be used as fertilizer. At present, the faster development of foreign composting methods for yard waste composting, manufacturing organic composite fertilizer technology. China's commonly used domestic waste composting technology is mainly simple high-temperature composting technology, mechanized high-temperature composting technology.
1.3.2 Problems with the composting method
The low level of technology of composting processing equipment, easy to produce bad odors during fermentation, the process conditions are difficult to control, and it is difficult to ensure that the composting facilities for long-term, continuous, stable operation, low composting efficiency. At the same time, the harmful components in the garbage caused serious pollution of the atmosphere, soil and water, not only destroying the ecological environment, but also seriously endangering human health.
1.4 Anaerobic fermentation technology
Anaerobic fermentation technology can better realize the resourcefulness, harmlessness and reduction of domestic waste.In 2006, the total number of anaerobic fermentation plants operated and built in Europe reached 124 (Kelleher, 2007). At present, anaerobic fermentation technology is gradually developing in the country with the gradual construction of anaerobic fermentation treatment plants. 1.4.1 Technical Status of Anaerobic Fermentation Treatment
Anaerobic fermentation treatment refers to the decomposition of organic waste by microorganisms under specific anaerobic conditions, in which carbon, hydrogen and oxygen are converted into methane and carbon dioxide, while elements such as nitrogen, phosphorus and potassium are stored in the residue and converted into forms that are easily absorbed and utilized by plants and animals. Foreign anaerobic fermentation technologies mainly include high-temperature and medium-temperature anaerobic fermentation; dry fermentation and wet anaerobic fermentation; single-stage and multi-stage anaerobic fermentation. 1.4.2 Problems of Biogas Production by Fermentation
The direct anaerobic fermentation of general domestic waste to produce biogas is difficult, and it is not yet mature for engineering application, and not all domestic wastes are suitable for anaerobic fermentation to produce biogas. Therefore, in order to achieve the ideal disposal effect, firstly, the waste should be classified, and secondly, the production process should be strictly controlled.
2 Domestic and foreign domestic waste disposal technology development trend
Landfill technology as the traditional and final treatment of domestic waste, although the landfill disposal rate has a downward trend, but the landfill disposal still occupies an important position, especially in underdeveloped countries. Waste incineration has also become an important direction of China's waste disposal, with China's municipal waste incineration technology level continues to improve, incineration waste heat utilization, especially waste heat power generation has entered an accelerated start-up phase. At the same time, foreign countries are still steadily developing incineration power generation and anaerobic fermentation biogas production technology. Anaerobic fermentation plant is also gradually established in China.
However, due to the complexity of the components of domestic garbage, a single garbage treatment technology has certain drawbacks, resulting in secondary pollution or waste of resources, from the point of view of energy conservation, emission reduction and circular economy, garbage sorting and recycling, integrated garbage
Combined treatment is a development trend in the future. 2.1 The development of garbage sorting and recycling
The classified collection and recycling of domestic garbage is the pre-treatment of garbage, and it is the fundamental way to eradicate the pollution of domestic garbage and the prerequisite for the development of circular economy. Through classified collection, not only the resources can be recycled and utilized, but also the volume of the garbage becomes smaller, reducing the freight cost, lowering the difficulty of garbage disposal, and ultimately lowering the cost of garbage disposal. At the same time, separate collection of garbage can simplify the garbage treatment technology and improve the efficiency of garbage treatment. After the garbage is classified and collected, the combustible components can be incinerated to generate electricity and improve the thermal efficiency; the easily degradable organic matter can be sorted out for composting and the quality of compost can be improved; and the content of wet and toxic garbage in the garbage used for landfill can be reduced to reduce the environmental pollution.
At present, the classification of life technology in advanced foreign developed countries, strict supervision, in Japan, garbage classification has become a citizen's habits and the general requirements of society, while in China, at present, most of the city's living garbage is still used in the mixed collection of large quantities of hazardous substances, such as dry batteries, waste lamps, etc., without classification directly into the landfill, not only increased the transportation of garbage and the amount of landfill, but also Not only increase the amount of garbage transportation and landfill, but also increase the difficulty of harmless treatment of garbage, so far there is no city in the country to fully implement the classification of garbage collection.
So, China should learn from foreign developed countries to realize the classification of garbage, first of all, we should improve the residents' awareness of environmental protection, so that the classification of garbage collection of the people; learn from foreign experience, advocate the use of garbage bags (canisters) system; to build the industrial chain of garbage recycling; sound laws and regulations, policy guidance, government regulation and control.
2.2 Garbage incineration power generation technology
The incineration power generation of municipal household garbage refers to the use of incinerators to incinerate combustible substances in household garbage, eliminating a large number of hazardous substances in the garbage through high-temperature incineration to achieve harmlessness and minimization of the purpose, and at the same time, using the recovered heat energy for heat supply and power supply to achieve the resourcing of the garbage incineration of the inert residue produced Can be disposed of in landfills, or as secondary building materials to be used, incineration of 2 tons of garbage produces heat equivalent to about 1 ton of coal.
Waste-to-energy in developed countries has been a mature industry and entered the industrialization, market-oriented maturity. Developed countries have examined the environmental friendliness of waste incineration power generation technology, incineration power generation technology is more and more widely used in developed countries.
China began to introduce waste-to-energy incineration technology for the first time in 1985, and the Comprehensive Work Program for Energy Conservation and Emission Reduction and China's National Climate Change Response Program, both released in June 2007, encourage the development of waste-to-energy incineration as a waste treatment method to reduce carbon dioxide emissions. 2009, China has more than 140 waste-to-energy power plants, however, the main focus is distributed in the following areas In August 2010, Beijing Gaoyantun Waste Incineration Plant formally passed the on-site inspection of the completion of environmental protection acceptance by the Ministry of Environmental Protection of the People's Republic of China, and is the first modernized large-scale waste incineration plant in Beijing, which adopts the advanced mechanical grate furnace technology, and is able to ensure that the emission indexes of the air pollution generated by waste incineration can be controlled stricter than the national standards and local standards of Beijing Municipality. It is the first modernized large-scale garbage incineration plant in Beijing. It is expected that during the "Twelfth Five-Year Plan" period, China will add new domestic waste incineration power plant capacity of 80,000 to 100,000t / d, the new domestic waste incineration power plant 70 to 80 seats.
2.3 Cement kiln and waste incineration plant joint treatment
Developed countries have sought new domestic waste treatment technology to industrial synergistic treatment
The waste treatment technology has gradually become a new point of view for the treatment of domestic waste, the existing industry to deal with solid waste can not only eliminate the waste pollution of the environment, but also provide raw materials and fuel for existing industries. Foreign countries have developed a variety of cement industry and domestic waste co-processing technology, and achieved significant results, such as Japan's cement plant to waste incineration plant incineration of domestic waste generated by the ash, fly ash and other wastes as a substitute for the production of cement raw materials.
Because of the special nature of our garbage, the treatment technology of developed countries, can only learn from, therefore, must develop a suitable for our garbage composition and characteristics of the cement industry domestic waste treatment technology. At present, China has successfully developed cement kiln and garbage incinerator joint technology, refers to the cement rotary kiln set up next to the garbage incinerator, by the cement kiln and incinerator joint treatment of domestic garbage, the technology can be fully utilized garbage heat and ash, low pollutant emissions, do not need secondary treatment, investment savings, low cost. The treatment technology does not need additional fuel, the garbage incineration temperature up to 900 ℃, in line with the temperature control requirements of incineration of garbage, the flue gas at 850 ℃ above the residence time of more than 2s, to prevent the generation of dioxin. Incineration of garbage plays the role of a substitute for fuel, and can realize the harmlessness, resourcefulness and residue-free treatment of garbage.
2.4 Cement kiln incineration - anaerobic digestion process joint
Use of cement kiln synergistic integrated treatment of domestic waste, such as cement kiln - anaerobic digestion technology joint treatment of domestic waste for China's domestic waste diversified treatment of a new model.
After sorting the garbage, the combustible components can be used for cement kiln or incineration plant incineration energy, while the organic perishable garbage using anaerobic digestion technology, especially suitable for high moisture content, easy to degrade organic matter treatment. In the process of anaerobic digestion, most of the carbon of the organic matter is released in the form of biogas and some carbon dioxide for treatment, and the biogas can be used for power generation after purification and treatment, and the hot tail gas after power generation can be used as a drying heat source for alternative fuels.
Cement kiln co-processing in the kiln temperature is high, can ensure that the organic matter incineration completely; materials and gases in the kiln to stay a long time, there is sufficient incineration time; the cement kiln volume is large, thermal stability is good, can provide continuous and stable incineration environment; cement kiln is alkaline, easy to purify the waste gas treatment, heavy metals will also be carried out on the lattice of the relevant minerals **** dissolved without causing secondary pollution.
3 Conclusion
Currently, domestic and foreign waste treatment technology for landfill, composting, incineration, fermentation, and a single waste treatment technology has certain drawbacks, with the countries of energy conservation and emission reduction and the development of a circular economy and further improve the environment, waste classification, recycling, incineration and power generation technology, integrated waste management technology, gradually become the development trend of waste treatment.