Cities are an important part of human survival and development as a whole, involving all aspects of human activity, is the concentrated expression of the achievements of human civilization. From 1950 to 2000 the proportion of urban population in developing countries rose from 17% to 42.1%, and it is predicted that by 2025 more than half of the population in developing countries will live in cities. The expansion of cities and the proliferation of urban populations have resulted in poor housing conditions and inadequate municipal and health services. The growing size of cities, the increasing population and the fragility of the ecological environment have led to the deterioration of the human settlement situation, and human beings have become more and more vulnerable to the aggression of disasters such as earthquakes, fires, public hazards and epidemics, as well as exacerbating the vicious circle of poverty and ecological environment. Therefore, the problems of environmental pollution and ecological deterioration brought about by urbanization have become a matter of common concern for all countries in the world***, and urban living waste has become one of the public hazards in the world today. With the rapid development of the economy, urbanization and consumption levels continue to increase, the production of domestic waste is increasing day by day, urban waste disposal has become a major factor affecting environmental protection, urban construction, residents' lives and sustainable development, a large number of open piles of domestic garbage and simple landfill disposal will cause great harm to the environment:
Take up a large amount of land resources, and cause pollution to the soil;
The high concentration of osmotic liquid produced by the pile is a serious pollution of water resources;
The large amount of noxious gases produced by the pile is a serious pollution of the atmosphere;
The pile causes mosquitoes and flies to breed, and spreads diseases, which affects the environmental hygiene and health of the residents.
In China's nearly 700 cities, two-thirds of them are surrounded by "mountains of garbage". In the past 10 years, China's urban garbage production to an average annual growth rate of 6.98%, a few cities, the growth rate of up to 15% -20%. In this regard, relevant experts pointed out: most of China's urban garbage is still mixed collection, garbage disposal is difficult, garbage treatment plant construction investment and high operating costs. The garbage problem has actually hindered the further improvement of people's living standard and the further development of urban construction. Therefore, it is particularly important to solve the problem of urban garbage disposal.
I. Current Situation
Chongqing is located in the upper reaches of the Yangtze River, in the central region of China and the western region of the combination of a special location, is located in the longitude of 105 ° 17 ′ - 110 ° 11 ′, latitude 28 ° 10 ′ - 32 ° 13 ′, the climate of subtropical monsoon Humid climate, the average annual temperature is about 18 ℃, less frost and snow throughout the year, more clouds, warm winter, summer heat, early spring, short fall, abundant rainfall, annual precipitation of 1000 ~ 1400 mm. The city has a total population of 30,596,900, of which 24,456,700 are agricultural, accounting for 80.91% of the total population, and 5,771,000 are non-agricultural. It is reported that the city of Chongqing now produces 8,000 tons of garbage per day, which is basically landfilled (not sanitary landfill) after simple selection by "scavengers". This not only occupies a large amount of land, but also brings potential, huge harmful leachate and harmful air pollution sources to the people; at the same time, it also makes the garbage in the huge economic benefits are lost in vain, waste.
Today's waste disposal methods mainly include sanitary landfill, incineration and comprehensive utilization (such as the production of organic compost, the production of building materials, heating and power generation, etc.), each with its own advantages and disadvantages. Through our investigation and research, we have concluded that in order to solve the garbage problem completely we should start from the source and carry out comprehensive management in order to realize the resourcefulness and harmlessness of garbage disposal.
The garbage disposal sites in Chongqing Municipality are generally overloaded with overflowing capacity, poor operation and management, difficulties in pollution control, and safety hazards. On the one hand, the main city of Chongqing Municipality's eight garbage disposal site, mostly built in 1985 ~ 1990, the construction scale and capacity is basically according to the urban garbage production at the time of the completion of the site, is now far from meeting the needs. On the other hand, from 1997 onwards, the planning and construction of the south bank of Changsheng, Jiangbei black stone, Beibei with the construction of three new garbage disposal site failed to be implemented according to the original plan, which makes the nineties of the eight garbage disposal site transition period of use, has been extended to the present.
Two, compositional analysis
1 from the high calorific value conversion
Three, the collection of garbage, transportation
Through the survey, we learned that today's garbage collection, transportation, there are the following problems:
1. Due to the quality of China's residents and other reasons, the city garbage has not been classified and recycled. Even in some areas of the classification of collection, in the transportation of mixed transportation. This greatly increases the difficulty of resourceful and harmless treatment of domestic garbage.
2. Garbage recycling and treatment costs are completely separate, mainly in the recycling system's own cost law to guide the operation. As a result, some of the recycling value of low or no recycling value (such as plastic bags, batteries, organic waste, etc.) will be no one recycling or unwilling to recycle, while newspapers, metal cans, glass, etc. Recycling rate has been high.
3. Household hazardous and toxic waste collection system has not been established. Household hazardous and toxic waste such as used batteries, fluorescent tubes, used medicines and electronic waste are mostly mixed into the municipal waste. This will bring potential environmental pollution, and also increase the operating costs of treatment.
Improvements:
1, the collection of garbage classification must be the participation of all the people, through publicity, activities to improve the environmental awareness of the whole population, to establish a "everyone participates in environmental protection, everyone attaches importance to environmental protection" style, so as to treat the symptoms of the root cause of the problem of garbage classification, collection, treatment.
2, to realize the city's waste classification and recycling in a short period of time is almost impossible, so it is recommended to carry out pilot projects in residential areas. And will be recycling and transportation supporting a combination of places to achieve the classification of waste separate recycling and transportation. It avoids mixing the separated garbage again during transportation.
3, the government's policy inclination, the money saved for waste classification will be subsidized due to the increased cost of separate transportation.
4, charges for unsegregated garbage, which can improve people's consciousness of garbage classification, but also subsidize part of the funds for garbage disposal.
Four garbage disposal
1, urban living garbage disposal
According to the investigation of Chongqing city living garbage in the physical composition and chemical characteristics of certain characteristics (see Table II, Table III, Table IV) by the chemical composition table can be seen: investigated by the main city of the four districts of the living garbage in the total nitrogen content is generally high, but the variation is not too large, the average value of about 1.24%. The average value is about 1.24%. It can be seen that there are more nitrogen-containing substances in the perishable organic matter fraction of domestic waste in the main urban areas of Chongqing (mainly due to the excessive amount of food waste and the well-developed catering industry). Plus, the average ratio of total C to total N (C/N) is 25.51, which is conducive to biological growth; at the same time, taking into account that the garbage also contains a certain amount of CL and S elements if the use of incineration will bring about a certain degree of air pollution, and thus it is appropriate to use composting or landfill technology (attention should be paid to the collection and treatment of odors, dust, and seepage liquid in the process of treatment to prevent the occurrence of secondary pollution). Of course, taking into account the lower ash content and higher calorific value of the waste, incineration technology can also be utilized for treatment (provided that the exhaust gas treatment system should be quite perfect can effectively deal with the pollutants in the exhaust gas).
2, hazardous and toxic waste disposal
Hazardous and toxic waste mainly includes rubber and leather, plastics, heavy metals, batteries, medical waste and so on. The survey found that the main city of Chongqing, the content of the above substances is not high, but because of the toxicity of these substances at the same time there is a "cumulative effect", so we must strictly control their emissions.
(1)Recycling and Treatment of Rubber and Leather
From the data of the survey (see Table 1), it can be seen that the proportion of leather and rubber in the garbage is not too large, however, its harmfulness and secondary pollution are very serious, therefore, we must be more vigilant and strictly control its emissions.
Survey found that leather rubber mainly from waste tires. Waste tires long-term open piles, not only cause a huge waste of renewable resources, but also easy to breed mosquitoes and insects, over time will naturally cause a fire; at the same time in the slow decomposition process will also release harmful gases to pollute the environment.
Currently, there are six main treatment methods for waste tires: overall reuse, production of rubber powder, incineration to energy, pyrolysis recycling and landfill energy storage. Regardless of the method, in general follow the "four R principle" that is to reduce the source of waste, reuse, recycling and recovery. From the point of view of resource utilization and environmental protection, the principle of "waste source reduction and material recycling" should be followed first, and then chemical recycling and energy recovery should be considered.
(2) recycling and treatment of waste plastics
Plastics generally refers to natural or synthetic polymer compounds as the basic ingredients, can be plasticized under certain conditions, and the final shape of the product properties remain unchanged solid materials. In the production of plastics, consumption pathway of each link will produce waste and waste products. Waste bags, plastic films and disposable lunch boxes used in our daily life are its main sources. As can be seen from Table 3, plastics account for a considerable proportion of Chongqing's domestic waste. At present, the country does not have a relatively perfect plastic treatment process. According to the plastic is generally not easy to decompose, into the soil after a long period of time does not decay, occupy a lot of land resources, and affect the permeability of the soil and water permeability, damage to the soil quality, serious harm to the growth of plants, reduce the use of land value of the characteristics of the proposed use of landfill, composting process; of course, you can also use the incineration technology, but the tail gas treatment is a technical problem, it is recommended to use incineration -Landfill comprehensive treatment process (see later discussion).
(3) Battery recycling and treatment.
Investigation found that the amount of waste batteries is not too large, mainly concentrated in Shapingba District. Because of this district for the education area, universities and colleges of students accounted for the vast majority of the total population, and students with the Walkman, calculators, torches, cameras, etc., a large number of batteries, making the amount of waste batteries increased dramatically. Waste batteries contain a lot of heavy metals. Waste alkali, waste acid, etc., in order to avoid its environmental pollution, harm and waste of resources, should first take the comprehensive utilization of methods, recycling and utilization of valuable elements, can not be used for harmless treatment of substances, to achieve the recovery of resources, the purpose of protecting the environment, for batteries in general using the direct method of process flow is as follows:
(4) Hospital garbage and dregs of recycling treatment
Hospitals and hospital institutions are the crowd and patients concentrated activities, treatment, inspection and living place. Not only produce general national waste and living garbage, there are a large number of biologically contaminated, with infectious garbage and waste, such as if not timely treatment of any of its emissions, it will pollute the atmosphere, water, soil and food, endangering human health. Physical sterilization, chemical sterilization, incineration and landfill disposal are generally used. After disinfection and sterilization or incineration of waste has eliminated the infectious, can be treated with the same process as general household waste.
(5) Recovery and treatment of heavy metals
Survey found that urban waste is often with a large number of heavy metal-containing waste such as: paint, cosmetics, paints and so on. These wastes containing heavy metals should be separated as far as possible, can be recycled in time, not timely recycling, according to its physical and chemical properties to be dealt with one by one, to prevent it from flowing into the environment, destroying the ecological balance and endangering people's health.
3, non-hazardous and non-toxic substances
Non-hazardous and non-toxic substances mainly refer to construction waste. Through the investigation, it is found that this part of waste in Chongqing is mainly concentrated in some high pay development zones Jiangbei and Jiulongpo District. For this part of the waste, due to its harmlessness, it is generally treated mainly by landfill, which does not require too high technical requirements.
V. Comprehensive treatment
1. Overview
At present, there are generally three kinds of waste treatment processes: composting, sanitary landfill and incineration. According to the survey found that simply using one of these processes to treat garbage is not very satisfactory. In view of the above shortcomings, we can composting, landfill and incineration of the three organic combination of comprehensive treatment, so as to maximize the recovery of usable components, effectively increase the processing efficiency, and ultimately achieve the "three" treatment, the process is as follows:
From the above process, we can see that: comprehensive treatment of the concentration of the landfill, Incineration and composting advantages, at the same time, also solved the shortcomings of a single treatment. Such as landfill shortcomings are: a, combustible material is not fully utilized; b, leachate treatment is difficult and costly; c, occupy a large amount of land. After the comprehensive treatment, putrescible organic matter and combustible organic matter are fully utilized, so the landfill volume is very small, accounting for only 15-20% of the total volume, and the landfill material is mainly bricks, rubble and other organic matter, which will not bring secondary pollution. This solves the shortcomings of single landfill brought about by the poor utilization rate of resource recycling, permeate treatment is difficult and occupy a large amount of land. Similarly, the shortcomings of single incineration belt can be overcome to some extent by comprehensive treatment. From Table 1, Chongqing local municipal solid waste contains high moisture content, sulfur content, to the incineration has brought some difficulties, the amount of flue gas emission is large, the incinerator corrosion is strong; if the integrated treatment is produced less flue gas, but also to avoid sulfur corrosion of the equipment. A single composting treatment can only deal with perishable organic matter in the garbage, other waste can not be dealt with, and comprehensive treatment can change its shortcomings. From the above analysis, the comprehensive treatment of both social benefits, or in the environmental benefits are much higher than a single treatment. On the one hand, there is no pollution emission, the amount of smoke, occupying less land, high resource recovery rate, effectively improve the environmental benefits; at the same time, the operating costs are lower, the service life of the equipment is extended, the investment in building plants is less, from a certain point of view, but also to improve a certain degree of social and economic benefits.
2, the realization of the "three" treatment
Resource system refers to the finished product from the raw materials processed by people, after people's consumption, become waste and introduced into the new production - consumption cycle system, which is a " It is a "waste to treasure", "production - consumption - waste - reproduction" continuous cycle of the system. Municipal waste contains a large number of recyclable paper, fibers, plastics, metals, glass, etc., we need to comprehensively deal with the overall situation, rationally and maximize its resourcefulness. The process is as follows:
(1) Pre-treatment
Through physical, chemical or biological methods such as compaction, crushing, dewatering, sorting and curing, solid waste is turned into a form that is easy to be transported, stored and recycled.
(2)Pyrolysis and incineration recovery
Pyrolysis utilizes the thermal instability of organic matter, and the process of thermal decomposition of organic matter under the conditions of anaerobic and anoxic conditions, which is a heat absorption process. Through pyrolysis can get low molecular compounds; gaseous hydrogen, methane, CO2, liquid methanol, acetaldehyde and other organic substances. Incineration is a high-temperature decomposition and deep oxidation process, which is not used for pyrolysis, it is an exothermic reaction, and the final products are CO2 and H2O. municipal waste can be incinerated to reduce the volume of 80% to 90%, and at the same time, it can be disinfected, sterilized, and decontaminated. The survey found that due to easy to cause secondary pollution (TCDD, CO2, etc.) and investment, high operating costs in Chongqing less application.
(3) microbial decomposition (landfill)
Nature exists in a large number of bacteria, actinomycetes and fungi and other microorganisms, we can make full use of microbial action and solid waste (organic matter) into stable humus, thereby improving the physical, chemical and biological properties of the soil, and promote crop growth. After investigation, we can conclude that the landfill site requirements are high, generally difficult to ensure that the incineration treatment cost is too high, the secondary pollution is serious; coupled with a lot of land, the amount of organic fertilizers required, and therefore, composting is a realistic, feasible, resourceful way to deal with waste.
(4)Classified collection
To improve the utilization rate of renewable resources, the most effective and important way is to produce a classified collection of garbage, and then classified collection of renewable resource materials for resource comprehensive treatment. However, the survey found that the current garbage collection and transportation system process is as follows:
This mixed collection, transportation, processing, will not only cause serious pollution, waste of a large number of renewable resources, but also to the treatment of the huge inconvenience, increased investment and operating costs. If the process is changed to classified collection of the following chart:
[1]Source reduction, expect zero discharge of domestic waste
[2]Upstream reduction, domestic waste for collection, transportation, processing before the consumer to sell some of the waste
Such after the classification of recycling, the amount of garbage can be reduced by 40 to 50%, the structure of the waste has undergone a fundamental change, by a variety of mixtures into a "single component", a single nature, the treatment of technical specialization, higher efficiency.
Through the survey and the above analysis can be concluded as follows:
1. The current situation of garbage disposal in Chongqing Municipality is poor, and there is no systematization and standardization from garbage collection, transportation, classification to disposal.
2. The garbage in Chongqing Municipality is characterized by high organic content as well as high calorific value, and has high potential for composting and incineration.
3.To treat the garbage better, it is recommended to combine composting and incineration with sanitary landfill for comprehensive treatment in order to realize reduction, harmlessness and resourcefulness.
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