The process of urbanization is one of the concentrated manifestations of the social and economic development level of modern human beings. Generally speaking, a country's urban level is the result of its economic development level. Judging from the long-term trend, China has indeed followed such a universal law. With the continuous improvement of China's economic level, large, medium and high-density cities, especially modern cities, appear constantly, accompanied by a large number of solid domestic garbage. The total amount of municipal solid domestic waste in China has always been in the forefront of high-yield countries in the world, and its growth rate ranks first in the world. The per capita output of urban solid domestic waste in 668 cities in China is 440 kg, with the annual total exceeding 654.38+600 million tons, accounting for more than 654.38+0/4 of the world total, and increasing at the rate of 8% ~ 654.38+00%, with a few cities accounting for 654.38+05% ~. Experts predict that the municipal waste in China will reach 264 million tons in 20 10, 409 million tons in 2030 and 528 million tons in 2050. Think about it, if so much garbage can't be treated by scientific means, the city will become a garbage city and the city residents will be surrounded by garbage. The treatment of municipal solid waste is a worldwide problem. Looking around the world, the main methods to solve the garbage problem are landfill, incineration, composting and pyrolysis.
Among them, the biggest feature of landfill treatment method is low treatment cost and simple method, but it is easy to cause secondary pollution of groundwater resources. In order to reduce the transportation cost, most urban garbage is stored in the open air or simply buried near the suburbs, which occupies and destroys the land resources on which human beings depend. The advantages of incineration treatment method are good reduction effect (after incineration, the volume of residue is reduced by more than 90%, and the weight is reduced by more than 80%), thorough treatment and little pollution. However, its initial investment cost is extremely expensive. It will cost about 700-800 million yuan to build an incinerator with a daily garbage disposal capacity of 1 1,000 tons and attached heat energy recovery equipment. In western developed countries, the application of waste incineration technology has been nearly 130 years, and it is still considered as one of the most effective and economical waste treatment technologies. Composting method is to produce compost by static fermentation of mixed garbage. Compost is suitable for the production of farm manure in rural areas, rather than the industrial treatment of urban garbage. Its disadvantage is that organic matter accumulates and decays for a long time, which usually takes three weeks to one month. The accumulated pollution is serious, mosquitoes and flies breed, which seriously pollutes the surrounding environment and brings great hidden dangers to local health and epidemic prevention. Organic matter is not completely degraded and fully treated, and the residue will still cause garbage pollution. Organic compost products contain many impurities, which can not effectively separate harmful substances such as heavy metals. Long-term use of compost products will cause soil surface deposition, destroy soil and endanger crops.
Domestic waste is a mixture containing a lot of kitchen waste and organic waste, which directly affects the ecological environment and people's quality of life. However, with the progress of science and technology, people gradually realize that garbage is a misplaced resource. After some harmless treatment, it can not only reduce the amount, but also become a new resource.
Classification and Transfer of Domestic Waste
In order to better treat and utilize domestic waste, it is necessary to classify it. Different treatment methods are adopted according to different categories. Garbage classification refers to the classification of garbage into several different categories according to different components, attributes, utilization value and environmental impact, and according to the requirements of different disposal methods. Domestic garbage can generally be divided into four categories: recyclable garbage, kitchen garbage, harmful waste and other garbage.
Recyclable garbage. Include paper, metal, plastic, glass, etc. Through comprehensive treatment and recycling, pollution can be reduced and resources can be saved. For example, every 1 ton of waste paper can be recycled into 850 kilograms of paper, saving 300 kilograms of wood and reducing pollution by 74% compared with the same output; Every 1 ton plastic beverage bottle can recover 0.7 tons of secondary raw materials; Every recovered 1 ton of scrap steel can produce 0.9 tons of steel, which saves 47% cost compared with ore smelting, reduces air pollution by 75%, and reduces water pollution and solid waste by 97%.
Kitchen garbage. Including leftovers, bones, vegetable roots, leaves and other food wastes, can produce 0.3 tons of organic fertilizer per ton by on-site composting with biotechnology.
Hazardous waste. Including waste batteries, waste fluorescent tubes, waste water silver thermometers, expired drugs, etc. These wastes need special safety treatment.
Other rubbish. Including bricks, tiles, ceramics, muck, toilet waste paper and other wastes that are difficult to recycle, sanitary landfill can effectively reduce the pollution of groundwater, surface water, soil and air.
However, garbage sorting is not easy. Thousands of city residents produce a lot of garbage every day. The city in the future will establish a garbage collection and treatment system through modern technology. Encourage urban residents to consciously classify glass, metals, fabrics, waste paper, household appliances, batteries, organic garbage, etc. Put different kinds of garbage into different color trash cans. There are three kinds of trash cans with different colors. One color trash can contains food garbage, one color trash can contains ordinary garbage, and the other color trash can contains dangerous garbage. Even if some residents don't sort garbage for the time being, with the development of human computer technology, the future trash can will be intelligent and have the functions of vision and smell. The intelligent garbage can intelligently identify the garbage poured into it, and the detection device installed in the garbage can classify the garbage by using the difference of some attributes of the garbage. For example, using the magnetic and non-magnetic differences in garbage to classify; Classification according to different particle sizes; According to the different specific gravity, there are gravity separation, magnetic separation, eddy current separation and optical separation. After the identification is completed, the garbage is automatically classified by the control system. When the garbage is almost full, the smart trash can will compress and package the classified garbage.
In view of the organic compound garbage such as food garbage, weeds and plant garbage in human life, every family will set up a special biological trash can in the future. Biological waste refers to degradable organic compounds, such as leftover food, weeds and plants. This kind of garbage can automatically decompose the organic garbage poured into it and turn it into fertilizer that can be fertilized. Urban residents can make their own fertilizers free of charge while disposing of garbage.
After the garbage is sorted, it can't be put in the trash can all the time, but it should be shipped out, otherwise the city will become a garbage mountain. At present, the more advanced method of transferring garbage is pipeline transportation. In Sweden, Japan and the United States, some cities use pipelines to transport garbage, and some garbage trucks have been cancelled. This is the most promising garbage transportation mode at present. The lower end of the smart trash can will be connected with underground pipelines, and the underground pipelines extending in all directions will send the garbage to the garbage disposal mechanism for recycling. Garbage disposal institutions recycle reusable plastics, paper, rubber, metal, glass, etc. Send it to the recycling plant, and send the high calorific value garbage with no recycling value to the incineration plant for power generation. After deep processing, it can also be made into auxiliary fuel for other industries. Other things can be sent to compost, and the organic matter in it can be refined into organic fertilizer after secondary fermentation, which can be used for landscaping. After this treatment, inorganic substances and other unrecoverable garbage have been greatly reduced and made harmless, and then sent to landfill.
trash recycling
China is a "populous country", which means we are also a "garbage country". According to statistics of relevant departments, the total amount of urban garbage in China alone reaches 654.38+0.5 billion tons every year. For its treatment, the original "moving policy" is basically adopted, which not only sows bacteria, pollutes the environment, but even destroys the ecological balance. At the same time, the relatively primitive garbage disposal method also causes the loss of renewable resources worth as much as 25 billion yuan per year.
In fact, there are many things that can be recycled, such as the reproduction of waste paper and scrap iron; Reuse of some packages; Some resources can be transformed into new production factors through energy conversion (garbage biogas power generation), and return to the cycle of production and consumption, that is, scientifically and reasonably treat garbage.
Experts from the Emerging Prediction Committee of the United States and the Japan Science and Technology Agency predict that in the next 30 years, there will be "Top Ten Emerging Technologies" in the fields of energy, environment, agriculture, food, information technology, manufacturing and medicine, among which emerging technologies related to garbage disposal rank second. With the emergence, maturity and industrialization of such emerging technologies, 50% of the daily life garbage in developed countries will be scientifically utilized by the first decade of the next century.
Utilize garbage to generate electricity
Electricity is an indispensable part of our real life. Life without electricity is unthinkable. We know that at present, "electricity" is mainly through the combustion of coal. In the combustion process, the water in the boiler is heated into high-pressure steam, and then the high-pressure steam drives the steam turbine to rotate at high speed, and the generator is driven to generate electricity through the coupling. The generated "electricity" is sent to the transmission line through the transformer, and then the voltage is changed into the voltage level used by users through the transformer, which is connected to various electrical appliances to make them run.
According to the introduction of the national resources department, China's coal reserves only have a mining period of 40 to 50 years. After 40 to 50 years, China's coal resources will be exhausted. We will face the day when there is no electricity. We can't imagine what our world would be like without electricity. There will be darkness around us, no telephone, no TV, no machine working, no information transmission, and so on, so if there is no electricity, how terrible our life will be. It pushes us back to the ancient past. Therefore, we must develop new energy sources.
In fact, all countries in the world are facing this grim fact. Scientists from all over the world, including China, are studying how to solve the problem of power generation after coal resources are exhausted in the future, so as to solve the indispensable "electricity" in people's lives.
At present, in addition to using atomic energy and renewable energy (hydropower, wind energy, solar energy, geothermal energy, ocean energy and biomass energy) to generate electricity, garbage is also studied. Garbage power generation not only cleans our environment, but also treats domestic garbage.
The European Parliament has specially approved a series of documents, requiring the landfill gas in EU countries to be collected and utilized. Austria, Sweden, France and other countries have successively promulgated laws and regulations on waste recycling, making waste recycling a new industry and developing vigorously. Switzerland and Denmark use waste incineration to generate electricity, accounting for 65% ~ 75% of the waste treatment capacity; By the end of the 20th century, there were 259 landfills in the United States, with an installed capacity of over 7.5 million kilowatts. The copper recovered from waste products in Japan accounts for 80% of the national copper demand.
As far as garbage power generation is concerned, the profits it brings are also considerable. At present, the heat generated by one ton of coal is 7000~8000 kcal, and the garbage is only about 3000 kcal. Garbage power generation can't compare with coal in calorific value, but compared with the cost of 500~600 yuan per ton of coal, garbage hardly needs cost, which makes the profit return of garbage power generation very rich. At present, the conversion of electric energy per ton of garbage in the United States is about 500~750 kilowatts, and it has reached 400~500 kilowatts in China. The net profit from garbage power generation is about 7%~9%.
The main method of using garbage to generate electricity is incineration. Incineration is a high-temperature thermochemical treatment technology of municipal solid waste. Garbage is sent into the furnace as solid fuel for burning. At the high temperature of 800℃ ~ 1000℃, the combustible components in the garbage react violently with oxygen in the air, releasing heat and transforming it into high-temperature combustion gas, and then into electric energy. Waste incineration technology has a long history of development in western developed countries. Germany and France are the first countries to use waste to generate electricity. In recent decades, the United States and Japan have also developed rapidly in garbage power generation and are in the leading ranks in the world. The research, development and application of waste incineration technology in China started late. In contrast, there is still a big gap in the design, production and application level and scale of waste incineration equipment in China compared with developed countries, but it has great potential and broad prospects.
In 2002, there were 660 cities in China, with an annual garbage removal capacity of 654.38+36.5 million tons. Considering that the average calorific value of garbage is 4200 kJ/kg, the annual total amount of garbage as energy is 573 kJ. According to the forecast of the State Environmental Protection Administration, the annual output of municipal solid waste in China will be 654.38+52 million tons in 20 10, 654.38+79 million tons in 2005 and 2 10 million tons in 2020. According to experts' estimation, in 2005, the organic matter content in garbage in large and medium-sized cities will reach more than 70%, and the water content will be around 50%. With measures such as garbage sorting, the domestic garbage in large and medium-sized cities will basically meet the requirements of direct incineration by 20 10. If the garbage that can meet this requirement accounts for 50% of the total amount, the calorific value is calculated at 5000 kJ/kg, and the total amount of garbage energy resources is 760 tons. If the same proportion is considered in 2020, the total amount of garbage energy resources is 1.050 coke, the available amount is 525 coke, and the available garbage power generation is 3450MW, providing about 25TWh of electricity. It is understood that so far, 20 waste incineration power plants have been built and put into operation in 15 cities such as Shenzhen, Shanghai and Zhuhai, and dozens of cities plan to burn 1000 tons of waste every day. Therefore, from the perspective of resources, garbage incineration has great potential for power generation.
Another technology that uses garbage to generate electricity is garbage biogas to generate electricity. In this way, the organic matter is concentrated and fermented in the biogas digester to produce combustible biogas, which is then transported to the power plant for power generation. Fermented organic matter can be used as fertilizer, which really kills two birds with one stone.
Garbage power generation organically combines environmental protection with energy saving, so it will have a good development prospect.
Turn garbage into fertilizer
Organic components in municipal solid waste, such as leftovers, can neither be reused nor used for power generation because of their low combustion value and high water content. Even so, we can't throw them away, which will breed all kinds of bacteria, flies, mosquitoes and so on, and will cause damage to the urban environment. At present, human beings mainly use compost to ferment this kind of garbage. The method of composting is to produce compost by static fermentation of mixed garbage. Compost is suitable for the production of farm manure in rural areas, rather than the industrial treatment of urban garbage. Its disadvantage is that the accumulation and decay time of organic matter is long, which usually takes 3 weeks 1 month. The accumulated pollution is serious, mosquitoes and flies breed, which seriously pollutes the surrounding environment and brings great hidden dangers to local health and epidemic prevention. Organic matter is not completely degraded and fully treated, and the residue will still cause garbage pollution. Organic compost products contain many impurities, which can not effectively separate harmful substances such as heavy metals. Long-term use of compost products will cause soil surface deposition, destroy soil and endanger crops.
With the rapid development of human biotechnology, human beings will widely apply microbial technology to the fertilization process of organic waste. Microbial waste treatment technology is to add microbial immobilized starter to kitchen organic waste, so that beneficial bacteria can "eat garbage". Our leftover rice, bacteria continue to eat, and the kitchen waste eaten by bacteria turns into bags of pale yellow powder, which is high-energy organic fertilizer. There are bones, plastic bags, chopsticks, and bacteria to eat. These garbage that can't be disposed of only account for 2% ~ 3% of the total kitchen garbage.
In this project of "turning decay into magic", the most important contribution is microbial technology. After 6-8 hours, under the action of certain temperature and humidity, the compound microbial bacteria can eat clean garbage and convert all animal and plant proteins into bacterial proteins. This bacterial protein can be used as both feed and fertilizer, which truly turns waste into treasure.
By using microbial technology, garbage disposal can reach 100%, and the utilization rate of resources can reach 95%. During this year's Beijing Olympic Games, the microbial waste treatment station separated from the athletes' restaurant is to treat the kitchen waste on the spot to achieve no transportation and no odor. It is reported that the mayors of many cities have visited the Olympic garbage disposal station, saying that it has jumped out of the strange circle of "turning one form of garbage into another". At the same time, another good effect has been achieved. For example, microbial agents continuously improve soil, increase soil organic matter content and balance soil pH. Although these can't be measured by price, scientific research has proved that increasing soil organic matter by 0. 1% per square meter can reduce 2.25 tons of carbon dioxide emissions. According to this calculation, if more than 2,000 square kilometers of fruit and vegetable bases adopt this microbial waste treatment technology, 8 million tons of carbon dioxide emissions can be reduced every year, so that the "fertile soil project" can be realized not far away.
In the future, every urban family will have this small machine with microbial treatment technology. People will feed leftovers to small machines after eating. This small machine spits out bagged fertilizer for the family garden. "This is amazing!" Future urban residents will get rid of the troubles caused by organic garbage such as leftovers.