With the development of economy, the acceleration of urbanization and the improvement of people's living standards, the discharge of garbage has increased rapidly. Every year, 654.38+000 billion tons of garbage are added. In view of the fact that garbage is flooding, countries all over the world no longer focus on the old problem of how to control and destroy garbage, but adopt positive attitudes and effective measures to treat and utilize garbage scientifically, list garbage as the "second resource" to maintain sustainable economic development, and ask garbage for resources, energy and benefits.
At present, the stock of garbage dumps in China has reached 6 billion tons for many years, occupying 500 million square meters of cultivated land. There are 660 cities in China, and 200 cities are surrounded by garbage. Taking the urban population of 260 million as an example, if each person produces 440 kilograms of garbage every year, the annual garbage output will be 65.438+0.654.38+0.40 billion t.
Houjie town, a big town with a population of over 73,000. In the early 1980s, due to the overall economic backwardness, houjie town's economic development was extremely poor. Because the government management system lags behind, the way to attract investment is getting narrower and narrower, and there is no industry at all, so there is no industrial waste. Moreover, the rural surplus labor force has not found a way out, and the rural economic level is very low, which is unimaginable. Economy is the foundation of the development of cultural consciousness. If the economy fails, people's consciousness, especially health consciousness, is also backward. At the same time, the government's lack of publicity, insufficient investment, overhead management and other reasons lead to chaotic and random treatment of rural domestic waste. In the early 1990s, the garbage mountain on Houjie Avenue was exposed by newspapers. Residents on both sides of Linxi dump garbage directly into the stream, and literally dump garbage everywhere on the hillside on both sides of the highway.
As for backward places such as remote mountainous areas, garbage is piled up at random in front of and behind houses, dead chickens and ducks are thrown into rivers at will, and pesticide bottles and garbage from health clinics are also thrown into roadside streams at will. In a village, there is a jingle: "Dump the garbage casually, don't turn around, or burn it casually, so as not to take it everywhere." This is a vivid portrayal of the way local people deal with garbage.
Later, although the government contracted the garbage disposal to individuals, due to neglect of management, the contractor did not really implement the responsibility and still could not change the current situation of littering. The quality of water resources in the upper reaches of Dongjiang River is being tested as never before, and cruel facts torture people's moral conscience. Here, we take Houjie, a representative rural town, as the research object, and analyze the present situation and countermeasures of rural domestic waste treatment.
From the 1950s to the mid-1960s, the contradiction of garbage pollution intensified. Since the mid-1960s, a series of disposal methods such as landfill, incineration and composting have been formed. For example, in the United States, 85% of garbage is treated by landfill, and only 10% is treated by incineration. Japan is a small country, only 26.9% of it is treated by landfill, while 665,438+0% is treated by incineration. Switzerland is also dominated by incineration, accounting for 53%. Several countries in western Europe give priority to landfill, and most of them control landfill. Since the 1970s, Japan, the United States, Britain, France and other countries have adopted the policy of "recycling" waste due to the crisis of resources and energy, and the treatment of garbage and feces has been developing in the direction of "recycling". Especially for garbage, 25.3% cities in Japan have carried out the activities of recycling garbage, and the amount of garbage recovered in 1976 reached 39 million tons, accounting for 49.5% of the garbage discharge in that year. In recent years, some countries have also developed the method of inorganic garbage dump, planting trees and flowers on the surface of garbage dump, developing street parks and beautifying cities.
The problem of rural domestic garbage disposal has its historical reasons, and it can never be solved overnight because of the restriction and influence of local economy, culture and customs. Our group analyzed the reasons: First, it is seriously restricted by the backward local economic development, and the economy is the foundation of everything. A large garbage dump needs to invest millions and tens of millions, and it needs the strong support of local finance. Secondly, it is deeply influenced by local people's living habits. For example, in rural areas such as mountains, people think that dead livestock must throw their bodies into streams to take away the musty smell. They just don't want to bury the body scientifically. The third government's propaganda is not enough or not at all, which leads to the backwardness of people's health awareness, which is closely related to the importance attached by government leaders. Fourth, the government's punishment for littering is not enough. Some good behavior habits are mostly punished at first. For example, Singapore's penalty for spitting is as high as S $500, equivalent to nearly RMB 3,000. Who will be willing to spend another 3,000 RMB to vomit? We believe that there will be good results under heavy punishment. Other reasons, such as the attention of government leaders and the supervision of superiors, can we learn from foreign experience, so I won't say here.
If the reason is found, it is good to prescribe the right medicine. Economic reasons are very important, but they are not something we can discuss and solve, so let's not consider them for the time being. However, people's behavior habits can be guaranteed through publicity, education and law enforcement by the government and other departments. The government can use propaganda cars, billboards, radio and television to publicize, educate and encourage people to dare to fight against littering. Only by mobilizing the whole people to participate can we achieve better results. In addition, good habits should start from an early age. Therefore, the effect of early education for children in kindergartens, primary schools and middle schools is definitely the best. As for those who are unconscious and morally corrupt, the government and relevant departments must not be soft!
1 Existing methods of municipal waste treatment
The goal of solving the garbage problem is to reduce the volume, quantity, recovery, energy and harmless treatment of garbage. At present, there are mainly three methods: landfill, composting and incineration.
1. 1 landfill treatment
Landfill has a long history and is a widely used treatment method. This method is widely used all over the world because of its simplicity, low investment and ability to deal with all kinds of garbage. From uncontrolled landfill to sanitary landfill, including leachate recycling landfill, compressed landfill and broken landfill.
Using landfill treatment method, we must first prevent the liquid leaching of garbage and the pollution of groundwater by rainwater runoff. The general specification requires that the elevation of the lowest part of backfill soil should be more than 3.3 m higher than the groundwater level, and the lower part of backfill soil should have an impermeable rock or clay layer. Otherwise, clay, asphalt, plastic film and other impervious layers need to be set separately. Secondly, the landfill should be equipped with an exhaust port, so that methane and other gases released during the decomposition of anaerobic microorganisms can escape in time to avoid explosion. Generally, it is not suitable to build houses on the backfill site within 20 years to avoid structural damage caused by uneven settlement of the backfill site, but it can be used as green space, farmland, pasture, etc.
As far as possible, use natural or artificial excavated depressions, waste clay pits, waste quarries, waste mines, etc. Landfill treatment should be selected after resource development. Landfill pits are conducive to restoring landforms and maintaining ecological balance, but if they are backfilled in large areas such as depressions, harbors and valleys. It is necessary to consider whether it will destroy the ecological balance.
1.2 composting
Composting is the oldest technology in China, India and other countries to treat garbage, manure and produce agricultural fertilizer, and it is also a method of research and utilization in the world today. Composting is a biochemical reaction of organic matter in garbage and feces under the action of microorganisms, which eventually forms a substance similar to humus soil and is used as fertilizer or soil improvement.
Composting is a biochemical process of decomposing organic components of garbage by microorganisms. In the process of biochemical reaction, organic matter, oxygen and bacteria interact to separate out carbon dioxide, water and heat, and at the same time generate humus.
The key of composting is to provide an active growth environment for microorganisms, thus accelerating the process of bacterial decomposition and stabilizing it. Composting is mainly controlled by nutrients, temperature, humidity, pH and other factors in garbage.
According to the principle of composting, it can be divided into anaerobic decomposition and aerobic decomposition. Anaerobic decomposition needs to be carried out under strict anoxic conditions. Anaerobic microorganisms decompose and grow slowly, so they are not used much. Aerobic decomposition can produce high temperature at the same time, which can kill sick eggs, bacteria and so on. Aerobic decomposition method is mainly used in China.
Composting technology is simple, which is suitable for the treatment of high-content garbage in Corruptible organics. It can make use of some components of garbage, and the investment in treating garbage with the same quality is much lower than that of simple incineration. Composting technology started earlier in Europe and America, and now it has reached the level of industrial application.
1.3 incineration treatment
Incineration refers to the process of combustibles in garbage burning with oxygen in an incinerator. The essence is the chemical reaction among carbon, hydrogen, sulfur and oxygen. Waste incineration releases heat energy, and at the same time produces flue gas and solid residue. Heat energy should be recovered, flue gas should be purified and residue should be digested, which is an essential process of incineration.
Incineration treatment technology is characterized by large capacity, good reduction and complete harmlessness. The heat generated in the incineration process can be used to generate electricity and realize the energy of garbage, so it is a kind of garbage treatment technology widely used in developed countries in the world.
Combustible solid waste can be oxidized and decomposed by incineration to achieve the purpose of detoxification, energy recovery and by-products. Almost all organic wastes can be treated by incineration. For inorganic-organic mixed solid waste, if the organic matter is toxic and harmful, it is generally best to use incineration. Incineration method is suitable for treating garbage with more combustible materials. When incineration is used, care must be taken not to cause secondary air pollution. Japan, Europe, Switzerland, Sweden and other countries have also developed high-temperature and medium-temperature decomposition based on the general incineration method, so that the garbage can be basically or completely burned at a high temperature above 1650℃, and the released energy can be recovered as energy.
Incineration is a garbage disposal technology that destroys garbage and uses heat energy. However, garbage incineration is only scientific and reasonable for those garbage that can't recycle valuable things but can only recycle heat energy.
2. Limitations of the existing urban garbage disposal methods
Limitations of landfill treatment
Landfill buries all available materials, and the selection of landfill becomes more and more difficult, and the cost of transportation, landfill and management is also increasing. Landfill covers a large area and has serious secondary pollution. For example, landfill leachate will pollute groundwater and soil, and the odor generated by garbage stacking will seriously affect the air quality around the site. In addition, methane gas produced by garbage fermentation is discharged into the atmosphere, which not only has the danger of fire and explosion, but also has a greenhouse effect. Moreover, the treatment capacity of landfill is limited, and it is still necessary to invest in building a new landfill after the service expires, further occupying land resources. Taking Beijing as an example, if the current technology is used to carry out sanitary landfill treatment of Beijing 12000t/d garbage, the construction investment alone will be as high as 720 million yuan (excluding land acquisition costs), and the life of the landfill is only 12a ... Based on the above reasons, since 1980s, sanitary landfill facilities abroad have gradually decreased, which has become an auxiliary method for other treatment processes to treat substances that cannot be reused.
2.2 limitations of composting
Compost can't treat non-perishable organic and inorganic substances, and the wastes such as stones, metals, glass and plastics in garbage can't be decomposed by microorganisms. These wastes must be classified and treated separately, so the degree of reduction, reduction and harmlessness is low Long composting period, large area and poor sanitary conditions; The fertilizer produced after composting is low in fertilizer efficiency, high in cost, harder to sell than chemical fertilizer and poor in economic benefit. The investment in introducing foreign technology is huge, which is not suitable for China's national conditions. Because the content of Corruptible organics in domestic waste in developed countries is far below the general level in China, only about 15% of the waste components can be composted, which hinders the popularization of composting technology to some extent. Composting technology must first classify fresh garbage and then ferment perishable organic components, so as to effectively prevent the infiltration of heavy metals, thus ensuring that organic fertilizer products meet national standards and truly realize harmlessness and resource utilization.
2.3 Limitations of incineration treatment
Incineration treatment has certain requirements for low calorific value of garbage, and not all garbage can be incinerated. Destroying the available resources in garbage is a waste of resources. Even if heat energy is recovered, it can only achieve the purpose of one-time regeneration of waste, and it is impossible to recycle resources many times. A large amount of flue gas produced by incineration is a huge loss of heat energy. The generated flue gas must be purified, and the purification technology is difficult and the operation cost is high. Residues from incineration must also be digested. In addition, incineration equipment has a large one-time investment and high operating cost.
3 Comprehensive utilization and treatment methods of urban garbage
Table 1 shows the garbage disposal methods in the United States and the proportion in each year. Comprehensive utilization should include the following aspects:
(1) Recycling of usable materials (waste paper, metal, glass, etc. );
(2) Composting in Corruptible organics;
(3) Energy utilization of non-perishable organic matter with high calorific value;
(4) Solidification treatment of ash, realizing the materialization of ash.
The practice of garbage disposal in many countries shows that 70% of it can be recycled and reused as renewable raw materials. Urban garbage is called "urban mineral resources" and is the only growing resource. There are dozens of garbage disposal plants in the world that recycle useful ingredients. These treatment plants were built in developed countries in recent 10 years. Practice has proved that they have opened up a new road for the rational and economical utilization of garbage resources and a new world in the field of garbage disposal. From the passive and limited stage of garbage destruction to the new stage of active and rational utilization of garbage.
The present situation and treatment of rural domestic garbage is not optimistic, not only in houjie town, but also in many places in the upper reaches of Dongjiang River. Due to various reasons, there are more or less some problems. As students and people of insight who love environmental protection, we can only do a few things, but there are still many things we want to do. How we hope that more and more people will care about our environment and our planet, because:
None of the garbage disposal technologies adopted in China can independently achieve the overall goal of recycling, harmlessness and reduction of garbage. With the progress of society and the improvement of people's living standards, the composition of garbage is becoming more and more complex, and there are more and more organic and synthetic substances. This situation requires the transformation of garbage disposal technology from a single destruction mode to a comprehensive treatment mode of multiple ways and mutual assistance and cooperation. Only in this way can we turn waste into treasure and provide available resources for the society.