Solid waste, referred to as "waste" for short, also known as "garbage", is a variety of solid or semi-solid (slurry) substances that are constantly abandoned in the process of human production and life. It should be pointed out that the concept of waste is relative, that is, the solid waste produced in a certain process may be the "pollution source" of soil, water and atmospheric environment; However, with the change of time and space, it can play a role again in the economic cycle and become the raw material of another process, that is, the recycled "secondary resources". With the progress of ideas and technology, we will have a brand-new understanding when we make a scientific investigation of waste from a different angle. Such as waste paper, can become the raw material of recycled pulp production, that is, in the later process, waste paper is no longer waste. Therefore, some people regard solid waste as "misplaced resources".
At present, on a global scale, solid waste has caused various hazards to the geological environment and ecological environment, which has caused many countries and regions to suffer greatly. This not only poses a threat to social progress and contemporary human health, but also endangers the development of future generations and the sustained prosperity of 2 1 century. How to safely discharge and treat the constantly generated solid waste has been highly valued by all countries in the world. Among them, actively carrying out the research on the discharge and disposal of solid waste and environmental geological problems is to make human activities and the surrounding ecological environment efficient and harmonious, that is, to make efficient use of the huge self-purification power of the environment, to make the ecosystem benefit the highest, to be in harmony with the environment, not to destroy the fragile earth ecological environment, to minimize the risk of ecological environment deterioration, to protect and promote the development of geological ecological environment to a virtuous circle, and to ensure sustainable development.
4. 1.2 generation of solid waste
The production of solid waste has its inevitability. It is no exaggeration to say that as long as there are human life and production activities, there will always be and continue to produce waste. In the process of acquiring and utilizing natural resources to engage in all aspects of production and life, due to the limitations of subjective and objective conditions such as time conditions, scientific and technological conditions, production purposes and economic benefits, people always throw some of them away as waste and garbage. Even the successful products of a certain era will become waste with the upgrading of products that have exceeded their normal service life or improved their living standards. Especially in the second half of the last century, with the rapid growth of the world population, the acceleration of urbanization and the rapid development of science and technology and the improvement of living standards, the waste produced by activities such as industry, agriculture and family, including composition, quantity and types, is constantly increasing and changing. The environmental geological problems caused by this are also constantly changing. According to the statistics in 1990s, the annual output of garbage in the world has exceeded 100× 108t, which is 30× 108t in the United States alone and 22× 108t in Europe.
In a sense, by the second half of 2 1 century, science and technology and production technology will certainly make great progress, and the production of solid waste is inevitable. Of course, the amount of waste will be less than today. However, the new environmental geological problems caused by new wastes generated by new technologies, such as toxic organic pollution that western countries attach great importance to in recent years, mostly come from high-tech synthetic materials, many of which are "three-to-one-supplement" substances with low content but high toxicity. Therefore, although the amount of new waste is small, the harm to the environment can not be ignored.
4. 1.3 Classification and characteristics of solid waste
There are many classification methods of solid waste, which can be classified according to its source, chemical properties, hazard characteristics and management needs. Generally speaking, many countries are classified according to their sources. For example, European and American countries are divided into five categories according to the source of solid waste: industrial solid waste, mining solid waste, urban solid waste, agricultural solid waste and radioactive solid waste. The characteristics of various solid wastes are very different, resulting in different environmental geological problems.
4. 1.3. 1 industrial solid waste
Industrial solid waste refers to waste residue, waste, dust and sludge produced in the process of industrial production, processing and product use, and even in the process of controlling "industrial pollution". Most of them come from all aspects of industrial production activities, and some of them come from the circulation and consumption of products, including products that have exceeded their service life or become waste after upgrading.
According to statistics, the annual discharge of industrial solid waste in the United States 1980 was 4× 108t, and that in Japan 1982 was 3.2× 108t. The output of industrial solid waste in developed countries is increasing by 3.2% ~ 4.5% every year. At present, the annual industrial waste generated in the world is about 2 1× 108t, and the hazardous waste is about 3.4× 108t. The discharge of industrial solid waste in developing countries is also synchronized with their own economic growth rate, generally increasing by 2% ~ 3% every year, and some countries are slightly higher than industrialized countries. Backward production technology and extensive resource consumption lead to complex composition of industrial waste and serious compound pollution. What's more, it is willing to sacrifice the local environment for economic growth.
The main emission sources of industrial solid waste are metallurgical industry, petrochemical industry, food industry, paper industry, rubber tanning industry, chemical industry, motor industry, clothing industry and transportation industry.
Industrial solid waste has the characteristics of wide source, large discharge and large area. According to statistics, by 1990, the storage capacity of industrial and mining solid waste in China reached 64.8× 108t, covering an area of 583.9km2 Although the pollutants in different factories are different in composition, there are many pollutants in general, which are complex in composition, difficult to purify and even produce compound pollution. In particular, hazardous wastes produced in some chemical industries are flammable, corrosive and toxic, which can easily pollute air, water and soil, deteriorate the environment, or cause dangerous events such as combustion, explosion and poisoning. Moreover, it is harmful for a long time, which not only threatens the health of contemporary people, but also causes cancer by poisoning, and also affects future generations to cause deformity and disability.
4. 1.3.2 Mining solid waste
Mineral solid waste refers to all kinds of natural mineral resources, waste rocks, waste residues and tailings produced in the process of mineral exploitation and mineral processing.
The exploitation of mineral resources consumes two kinds of natural resources-mineral resources and environmental resources. The characteristics of solid waste produced by different mines are different. Especially in non-ferrous metal mines, the valuable components extracted from ores at present often account for only a small proportion (a few percent to a few thousandths), and from an industrial point of view, most of them have little recent use value and become waste rocks and waste residues. According to the data in the late 1970s, the annual output of mining solid waste in the United States alone is as high as 17× 108t. After these huge waste residues enter the environment, they not only change the original landform, but also cause various hazards to the environment. The interaction mechanism is complex, which directly or indirectly worsens the engineering geological environment.
For example, in metal and nonferrous metal mines, for every 1t ore produced, the waste rock stripped in the open air is about 4t, sometimes as high as 6 ~ 8t. Underground mining also needs to extract 0.5 ~ 1.5t more waste rock. A large number of waste rocks and low-grade slag often accumulate nearby along ditches and slopes, destroying the original vegetation ecosystem and becoming a part of modern artificial landforms. Especially in the mountainous areas of western China, the original geological and ecological environment is very fragile, and the drought and flood seasons are distinct. Mining waste piles piled up along ditches and slopes are prone to destructive landslides and mudslides. The more serious potential harm is realized in the long and slow evolution that is not easy to detect. Because the original underground closed oxygen-deficient environment of ore and surrounding rock has been artificially changed, mining waste rock and slag are broken, the surface area in contact with air is increased, and they are directly exposed to the open oxygen-rich environment on the surface, which accelerates the weathering process. Especially, the waste rocks of sulfide deposits, after being exposed to the sun and rain, have accelerated the diffusion of harmful heavy metal elements such as mercury (Hg), lead (Pb), cadmium (Cd), chromium (Cr), arsenic (As) and the leaching of harmful substances such as soluble sulfate, which have been washed away along the surface and migrated to the soil environment and water environment, poisoning the soil and polluting the water body, thus becoming a long-term potential pollution source. In particular, some nonferrous metals, rare earth minerals and phosphorite contain radioactive impurities, and the random stacking of mining waste rocks and slag will cause the diffusion and pollution of radioactive elements in the environment and aggravate the harm to the ecological environment.
Coal gangue is the waste rock produced by coal mining in energy coal mines, which is piled up in large quantities to form a black-gray artificial gangue hill landform, which not only destroys the harmony of the surrounding landscape, competes for cultivated land and fertile land, but also causes various environmental disasters. Long-term exposure of coal gangue to air accelerated the weathering process. On the one hand, coal gangue contains organic matter, pyrite and other components, which are easy to oxidize and spontaneously ignite, producing a large number of waste gases such as CO, NO2, SO2, H2S and benzopyrene, polluting the air environment, affecting people's health and causing high incidence of respiratory diseases and cancer. On the other hand, a large number of organic components, soluble sulfides, heavy metal salts, and even some coal gangue contain radioactive elements and impurities, which are dissolved and leaked by weathering and atmospheric rainfall, polluting surface water environment and even groundwater, such as Fushun coal mine area in China (Figure 4. 1). Gundam 199 1, about 1/3 of the 200 coal gangue mines in China spontaneously combust, such as most coal mines in Ningxia and the eastern and western mining areas of Xishan coalfield in Taiyuan, Shanxi. The spontaneous combustion of coal gangue hills in No.2 Mine of Jiaozuo, Pingdingshan and Yangquan Mining Bureau in Henan Province has seriously polluted the atmosphere. Mountains of coal gangue are also prone to weathering and instability, leading to landslides and mudslides. For example, in 1972, the rainstorm in Faroe Valley, West Virginia, USA caused the coal gangue debris flow disaster, and the coal gangue flow of 17× 108m3 pushed down 27km at a speed of 5.8m/s, resulting in16 deaths and 546 houses./kloc.
Fig. 4. 1 Distribution map of gangue hill in Fushun area
Tailing sand is an aggregate of rock powder particles with uniform texture produced by mineral processing and recovery of material components, which has economic value at present. Its impact on the environment depends on the chemical activity of harmful elements and substances, discharge location and disposal conditions. Due to the fine particle size of tailings, which is generally between 0.5 and 0.05 mm, it is easy to be lost due to strong wind and rain erosion, and it will enter the water body or soil environment, causing pollution hazards.
4. 1.3.3 municipal solid waste
Urban solid waste, commonly known as urban garbage and feces, mainly comes from urban residents' consumption, municipal construction and maintenance, commerce, culture, medical care and other activities. With the acceleration of urbanization, the rapid increase of urban population, the imbalance of urban operation function and the gradual improvement of living standards, the amount of urban solid waste has increased rapidly. According to the data of 1990s, the per capita annual emission of industrialized countries is 3 ~ 4t, and that of developing countries is about1~1.3t. ..
The composition of municipal waste varies with different countries, economic living standards and lifestyles, which makes the changes of fruits and vegetables obvious at any time.
The average annual growth rate of municipal solid waste in developed industrialized countries is 2% ~ 5%, and in some countries such as South Korea, it is as high as 1 1%, which is higher than that in developing countries as a whole. For example, the daily garbage output in new york is (2.2 ~ 2.4) ×104t; Cairo, the capital of Egypt, only produces 4000 tons of garbage every day. At the same time, the "economic value" of municipal solid waste components in economically developed countries is relatively higher than that in economically underdeveloped countries, and many of them are combustible and recyclable components (Table 4. 1). Especially in modern life, many convenient consumer goods, such as paper, plastic and other packaging materials, and even some large durable consumer goods, such as cars, refrigerators, washing machines, televisions and so on. , more and more abandoned because of the "outdated" upgrading, and the cycle of upgrading is getting shorter and shorter. For example, the mountains of abandoned cars and used tires in Japan and the United States have become an environmental disaster.
Table 4. 1 Garbage Statistics of Some Cities in Europe, America and Asia (wB/%)
Although the per capita daily output of municipal solid waste in China is small, ranging from 1.0 ~ 1.2kg, due to the large population base, the annual growth rate of municipal solid waste is about 10%, which is higher than that of industrialized countries. According to the statistical data of 199 1 year, the daily output of garbage in Beijing is1.1×104t; Guangzhou produces 2 860t tons of garbage every day; The government announced that the daily garbage output is1.3×104t; It is said that Shanghai produces about 8,000 tons of domestic garbage and 7,500 tons of feces every day. According to this calculation, only 10d garbage can be piled up into a garbage dump with the volume of "international hotel". With the continuous improvement of living standards, the change of urban fuel structure and consumption structure has changed from frugal to abandoned, and the composition of garbage has changed rapidly, especially the organic composition has increased, while the inorganic components such as furnace ash and cinder have decreased. Of course, as far as the current situation is concerned, the "economic value" of urban waste components in China is generally low. The characteristics of municipal solid waste in China are as follows: ① There are more inorganic components than organic components, and the ratio is about 2.5∶ 1. Especially in cities where the energy composition is mainly coal, the furnace ash accounts for 53.93% ~ 69.74%, and the organic composition of urban solid waste mainly gas rises from 30.26% ~ 37.67% to 86.94% ~ 92.6%. The daily output of garbage per capita is reduced to 0.39 ~ 0.86 kg. At present, the amount of inorganic cinder and ash in urban garbage is large, which makes the proportion of garbage with the same volume larger and increases the transportation cost of garbage. From another point of view, coal cinder is rich in ash, which can absorb a large amount of organic rotten leachate and odor, while gas-fired city garbage lacks ash adsorption from coal cinder, which looks particularly smelly when there is a large amount of organic matter. ② There are more incombustible components than combustible components in municipal solid waste, with the ratio of about 20∶ 1, which makes the incineration calorific value of solid waste low or unable to meet the requirements of energy generated by combustion, and the incineration capacity reduction effect is poor, even unable to be incinerated; (3) Mixed collection of municipal solid waste makes non-compostable components more than compostable components, and the ratio is about 4∶ 1. In particular, most of China's urban garbage treatment started late, and urban garbage was not collected separately, which made kitchen food garbage, daily necessities garbage, wheeled garbage bins, urban cleaning garbage and construction garbage mixed with industrial garbage, human and animal feces, hospital garbage, biological products factory garbage and other harmful waste, and the compound pollution was serious. Moreover, with the rapid expansion of urban area, the garbage dumps in the outer suburbs of the city have also become the suburbs of the city. In recent years, like the trend in developing countries, it has developed into a transfer trend of dumping garbage in the urban-rural fringe, "garbage surrounds the city." In remote sensing aerial photography, Shanghai has been surrounded by more than 500 garbage dumps, large and small; Before 1990, there were more than 4,500 garbage mountains with a height of more than 50m3 between the Third and Fourth Ring Roads in Beijing, and the whole urban area was almost surrounded by circular garbage groups.
Urban garbage is an unpleasant substance. It is characterized by complex organic components, rich in a variety of perishable pollution components, rich in nitrogen, sulfur, phosphorus, water, and even germs and viruses, which are easy to cross-infect various diseases. Under the action of anaerobic bacteria, these urban garbage dumps are prone to produce malodorous substances, such as H2S, azadirachtin and fecal odor. , and release a large number of harmful gases such as CO2, NH3 or CH4, while rotting, it overflows harmful secretions, attracts birds and insects, breeds mosquitoes and flies, easily causes infectious diseases, aggravates the deterioration of urban ecological environment, greatly affects urban environmental sanitation, and hinders the beauty of the landscape, which has become a major cancer in the development of modern cities.
4. 1.3.4 Agricultural solid waste
Agricultural solid waste refers to the waste discharged from extensive raw material processing and slaughter of agriculture, forestry, animal husbandry, sideline production and fishery products, which is referred to as agricultural waste for short.
It mainly comes from the improper use and disposal of forest cutting residues, agricultural grain straw residues, fruit and vegetable residues, livestock manure, animal carcasses, perishable agricultural and sideline products processing residues, waste materials, pesticides and fertilizers. In recent years, with the progress of agricultural science and technology, intensive agriculture and technology-intensive livestock and poultry breeding have developed rapidly, and the treatment capacity of agricultural waste has also increased accordingly. According to the data in the late 1970s, the annual output of agricultural solid waste in the United States reached 6.4× 108t. According to the statistics of the United Nations Environment Programme, nearly half of the solid waste in European countries comes from agriculture.
Because a large number of agricultural wastes are organic wastes, containing a certain amount of water, and sometimes containing many germs, viruses, parasitic eggs, pests and so on. They are all concentrated, they are easy to rot, and produce substances with color and smell, which makes the soil environment become an oxygen-deficient acidic reducing environment, greatly reducing the self-purification ability of the soil and breeding various pathogenic microorganisms, mice and flies. Its damage to the ecological environment directly accumulates some toxic and harmful substances in the soil, which makes the soil polluted and poisoned.
4. 1.3.5 radioactive solid waste
Include natural and man-made radioactive solid waste. Natural radioactive solid waste mainly comes from uranium, thorium nuclide ore and rare earth ore, as well as waste rock, waste residue and tailings produced by mineral processing in some non-ferrous metal mines. It even includes steel slag bricks containing excessive uranium and radium, granite building and decoration materials. Artificial radionuclide solid waste mainly includes radioactive isotope waste produced by nuclear industry, nuclear power, nuclear test and radiotherapy, scientific research laboratories and decommissioned nuclear facilities.
When it comes to "radioactive radiation", it is easy for people to have horrible associations and talk about nuclear discoloration. In fact, it should be rationally noted that natural radioactive radiation has been widely existed in various environments for 4.6 billion years since the formation of the earth. The history of biological evolution on earth has proved that moderate irradiation is not only harmless, but also beneficial to biology, which has been confirmed by nuclear medicine radiotherapy and agricultural seed irradiation technology, which can increase yield and improve quality.
Internationally, the quantity used to express radioactive intensity is called radioactivity, and the unit is Bq. Specific activity (Bq/kg) is called radioactivity per unit mass of substance. The so-called radioactivity means that the specific activity (Bq/kg) or concentration (Bq/L or Bq/m3) of solid waste is higher than the limit set by various countries, which may cause environmental harm.
That is to say, we should also clearly realize that excessive radiation is harmful, and its harm lies in that when the human body is exposed to excessive or long-term low-dose radiation, the molecular structure and properties of human cells will change through ionization and excitation, and then temporary or permanent damage will be caused to the body. It is generally believed that the biological effect of alpha-rays is great, but the penetration ability is small. In vitro, they do not pose a threat to tissues in the body, but they are more harmful when they enter the body. Gamma rays have a strong penetrating ability, even if they are irradiated in vitro, they can also cause damage to deep tissues. The function and ability of β -rays are between the first two. In a radioactive polluted environment, human body may be exposed to radiation from the outside, or may inhale polluted air or ingest food contaminated by strontium (90Sr), cesium (137Cs), iodine (13 1I) and carbon (14C), and these elements have a long half-life.
The pollution of radioactive waste to the environment is different from general chemical pollutants. At present, no chemical, physical or biological methods can effectively destroy these nuclides, and the harm they cause will only appear after a certain latent stage. The composition, nature and radioactivity level of radioactive waste from different sources are often very different, and it is usually impossible to distinguish whether it belongs to radioactive waste with the naked eye, but only with special instruments can it be found. On the other hand, once the symptoms harmful to human body are found, it is often in the late stage of accumulation. Therefore, the state has formulated strict management measures for radioactive solid waste, which is self-contained and specialized in management.
At present, there is no unified radioactive waste classification scheme in the world. Referring to the international general principles and the provisions of the International Atomic Energy Agency, combined with the actual situation in China, China has formulated Table 4.2 of the National Standard for Classification of Radioactive Solid Wastes (GB9 133). Radioactive solid waste is first divided into two categories: non-transuranic waste and transuranic waste, and then divided into four categories according to the length of half-life, and each category is divided into three levels according to the specific activity: low level, medium level and high level.
Table 4.2 Classification of Radioactive Solid Waste (Specific Activity A/BQ kg- 1)
To sum up, although the composition and characteristics of the five categories of solid waste from different sources are different, the harm and adverse consequences to the eco-geological environment are similar and the same. In order to meet the needs of solid waste management, China tends to divide solid waste into four categories: industrial and mining solid waste, hazardous solid waste, municipal garbage and feces, and others. Among them, industrial and mining solid waste refers to non-toxic and harmless industrial and mining solid waste. Hazardous solid waste is called hazardous waste internationally. But in fact, due to the types and properties of solid waste, especially in recent years, new materials and chemicals have proliferated. When they enter the environment, the compound reaction between them, the length of time they stay in the environment, and the harmful characteristics are still unclear. They are not as accurate and clear as "either/or", and even the definition and operation of hazardous nature are very difficult. There is no obvious boundary between hazardous waste and non-hazardous waste, that is, it is not easy to determine So far, there are different views on this issue in the world. Some countries define it according to its harm to human health, while others emphasize that it also includes its harm to the environment. Generally speaking, the so-called hazardous waste generally refers to solid waste other than radioactive waste, which is toxic, flammable, reactive, corrosive, explosive and infectious, so it may cause harm to human health and ecological environment. Although the hazardous waste generated in the world only accounts for about 3% of the total solid waste every year, about 3.4× 108t, most of which are solid wastes generated in the chemical industry, which can endanger the ecological environment and human health through various channels in all aspects of its generation, transportation, storage and even disposal. The United States accounts for about 80% of the total hazardous waste, with an annual output of about 2.4× 108t, Japan about 2,400×104t and European countries about (2,500 ~ 3,500 )×104t. In industrialized countries, hazardous waste has become a sensitive "political waste". In order to pass on the crisis of foreign garbage, especially hazardous garbage, it has been transferred across borders in various ways in recent years and exported to developing countries including China, endangering other countries. This has aroused the concern and resistance of many countries in the world. In order to strengthen the control of transboundary movements of hazardous wastes, 1989 In March, the United Nations Environment Programme held a conference in Basel, Switzerland, and adopted the Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and Their Disposal.