How Do I Earn an MSW?

Municipal solid waste refers to solid waste generated in urban daily life or activities that provide services for urban daily life, and solid waste considered as urban domestic waste by laws and administrative regulations, mainly including residential domestic waste, commercial waste, and market trade. Market garbage, street garbage, garbage in public places, government agencies, schools, factories and mines, etc. (except industrial solid waste and special waste such as hazardous solid waste). With the development of the city and the continuous improvement of people's living standards, the amount of domestic garbage generated in China has increased year by year, and the environmental pollution problems caused by it have become more and more serious.

The composition is complicated. At present, most cities in China use a mixed collection method instead of separate collection. Therefore, various types of garbage are mixed together and the composition is complex.

High moisture content. The garbage contains a lot of vegetable and fruit peels, so the moisture content is about 30% to 50%.

High content of inorganic substances. At present, most cities in China still use coal as the main fuel, and the content of inorganic substances such as coal slag, sand, metal, and glass is very high.

Less organic matter. Among the garbage in China, there is a lot of kitchen waste in organic matter, and the moisture content is high. Paper, plastic, wood, textiles, leather, and other high-calorie substances have less content and lower calorific value.

With the improvement of people's living standards, urban living gas is gradually popularized, the content of organic matter in urban waste will be greatly increased, and the calorific value of garbage will continue to increase. For example, the heat value of waste in Beijing has increased from an average of 3349kJ / kg per year in the late 1990s to an average of 5862kJ / kg per year ^[1]

The harm caused by urban domestic waste is not only reflected in the occupation of too much land, which creates a harsh environment surrounding the city, but also causes pollution to the atmospheric environment, groundwater sources, soil and crops. A large amount of harmful gases emitted by the deterioration of organic matter in the garbage entering the atmosphere will seriously pollute the environment. Affects the life and health of urban residents: harmful substances in garbage dissolve into groundwater and penetrate into the soil. Will cause pollution to groundwater sources and soil, endanger the health and life safety of people in the surrounding areas, and the harm of such pollution is difficult to eliminate.

In addition. The content of organic matter in municipal waste is relatively high, and the cattle biogas is produced after the waste is fermented. The main components of biogas are methane and carbon dioxide, which cause pollution to the atmosphere. Impedes vegetation growth and damages the ozone layer. Even more dangerous. The methane produced by the centralized waste storage is a flammable gas. When it is mixed with air to a certain proportion, it will explode when it encounters sparks, directly threatening people's lives and property. The garbage also contains pathogenic bacteria and parasite eggs and other factors that endanger human health, so improper handling will cause the spread of disease and affect the human living environment.

It should be seen that while municipal solid waste pollutes the environment. It is also a potential resource.

The garbage contains a large amount of combustible organic matter, which has a certain calorific value and can generate a certain amount of heat after incineration. Generally speaking, the heat produced by burning 3 t of garbage is equivalent to the heat produced by burning 1 t of medium heat coal. Therefore, a city's garbage is like a low-grade open-pit coal mine. Development can be cyclically performed over a long period of time.

In addition, the methane produced by landfills can also be used scientifically to benefit humanity. In short. Scientifically and rationally reduce, recycle, and harmlessly treat and utilize garbage. It is the need of human environmental protection. It is also the need for social development to recycle valuable materials.

The treatment and disposal of municipal solid waste has increasingly become a universal concern in the world, and it is a very difficult comprehensive and systematic project. At present, the treatment methods of municipal solid waste include landfill method, compost method, heat treatment method, worm method, forage, bacterial digestion, water-borne method, classification recovery, comprehensive utilization and so on. The main treatment methods are landfill method, compost method and heat treatment method. The current research and application focus at home and abroad is classified recycling, collection and resource recycling and comprehensive utilization of collected domestic garbage, reducing resource waste caused by traditional processing methods.

In China, the levels and methods of municipal solid waste treatment and disposal are quite different. The standardized treatment and disposal of municipal solid waste in most cities has just begun. Sanitary landfilling is the main treatment and disposal method for most municipal solid waste. The burial ground is running.

Municipal solid waste landfill

Landfill is the oldest way to dispose of garbage into the ground. From 3000 BC to 1000 BC, the capital of the Greek island of Crete, Conhonthos, is about to layer over the rubbish and bury it in a large pit. Because of its low investment cost, this method has been widely used in various countries around the world. At present, landfill technology has developed from uncontrolled landfill to sanitary landfill, such as new methods such as leaching and recycling landfills, compressed landfills, and broken landfills. The purpose is to avoid secondary pollution and ensure the safety of backfill sites And save investment.

Landfill construction includes site selection, design and construction, landfill waste entry, operation, closure, post-maintenance and management, and pollutant control and monitoring. The Ministry of Environmental Protection promulgated the Control Standards for Pollutants in Domestic Waste Landfill Sites (GB 16889-2008) in 2008, which provided detailed regulations on the control standards for pollutants in landfill construction.

During the revision of this standard, stricter requirements were imposed on pollutants control in the whole process of site selection, construction, operation and closure of domestic waste landfills. The standard supplements the requirements for the site selection of domestic waste landfills, the design and construction of basic facilities, and increases the entry requirements for general industrial solid wastes and domestic sewage treatment sludge that can enter the domestic waste landfills for co-processing. Certain wastes that meet the standards and meet the requirements of domestic garbage incineration fly ash and other wastes can enter domestic garbage landfills, which has greatly promoted the construction and operation of domestic garbage incineration facilities in China. The standard sets new requirements for the leachate treatment of domestic landfill sites. The standard stipulates that existing and newly-built domestic landfill sites should have relatively complete sewage treatment facilities. The leachate must be treated to meet the standard discharge requirements. Limits can be emitted. For the existing domestic waste landfill site standards within 3 years after the implementation of the discharge concentration limit requirements can not be met, should meet the domestic waste percolation after pretreatment, evenly injected into the urban secondary sewage treatment plant does not exceed the urban secondary sewage treatment The plant's rated sewage treatment capacity and other requirements can be used to send domestic garbage leachate to a municipal secondary sewage treatment plant for treatment. The standard also proposes strict monitoring measures for malodorous gases generated from domestic landfill sites, stipulating that methane gas should be comprehensively used and disposed of, which has played a positive role in global climate change, promotion of energy conservation and emission reduction, and construction of a recycling-oriented society.

Judging by the environmental protection measures (such as anti-seepage at the bottom of the site, sub-layer compaction, daily soil cover, landfill gas drainage, leachate treatment, pest control, etc.), and whether environmental protection standards are met, China's domestic waste landfill sites can be judged It is divided into three levels: simple landfill, controlled landfill and sanitary landfill.

(1) Simple landfill (Class IV landfill)

A simple landfill is a landfill that has been used in China for decades. Its main feature is that there are basically no environmental protection measures, and it is hard to say what environmental standards are adhered to. At present, a considerable number of domestic waste landfills in China belong to this type, which can be called open landfills, which have a greater pollution to the environment.

(2) Controlled landfill (level III landfill)

Controlled landfills also account for a large proportion in China. Its main characteristics are that some environmental protection facilities are equipped but not complete, or environmental protection equipment is complete, but it cannot fully meet environmental protection standards. The main problems are concentrated on anti-seepage at the bottom of the site, the treatment of leachate, and the failure of daily soil cover to meet environmental protection requirements, and there is a certain amount of environmental pollution.

(3) Sanitary landfill (grade , landfill)

Sanitary landfills are landfills that can control leachate and landfill gas, and are widely used in developed countries. Its main feature is that it has both perfect environmental protection measures and environmental protection requirements. The landfill is a closed or ecological landfill. Among them, Grade II landfill (basically harmless) currently accounts for about 15% in China, and Grade landfill (detoxification) currently accounts for about 5% in China. Xiaping in Shenzhen, Xingfeng in Guangzhou, and Laogang in Shanghai The waste sanitary landfill is its representative.

The choice of landfill site is the key to comprehensive design and planning of sanitary landfill site. Generally, two principles must be followed: first, site selection must meet environmental protection requirements, and second, it must be economically reasonable and feasible. The site selection, design, construction and acceptance of the garbage sanitary landfill site shall meet the requirements of the "Standard for Pollution Control of Domestic Waste Landfill Site" (GB 16889-2008).

The following factors are generally considered:

Garbage: Determine the size of the site according to the source, type, nature and quantity of garbage.

Terrain: To facilitate construction, avoid depressions, have strong drainage capacity, and be able to dispose of landfill waste for at least 20 years.

Soil: It is easy to obtain cover soil, soil is easy to compact, and has strong anti-seepage ability.

Hydrology: The bottom of the base layer of the landfill area should be kept at a distance of more than 1 m from the highest annual groundwater level.

Climate: It can evaporate large precipitation and avoid high and cold areas.

Noise: Noise from transportation and operation equipment does not affect the work and rest of nearby residents.

Transportation: Be convenient and have all-weather roads capable of transporting in various climates.

Distance and bearing: suitable transportation distance, located in the downwind direction of the city.

Land requisition: It should be easy to acquire and more economical.

The landfill method is the main method for the centralized disposal of urban garbage in China due to its simple technology and low processing cost. However, the landfill waste is not completely harmless, and there are a lot of bacteria, viruses, and hidden dangers such as biogas and heavy metal pollution: the leakage of garbage can cause secondary pollution, so this method is potentially harmful. The harm is greater, and it will bring future troubles to future generations. At present, many developed countries have explicitly banned landfill waste.

Municipal Solid Waste Composting Act

Compost is an organic fertilizer made from various plant residues (crop straw, weeds, leaves, peat, garbage, and other wastes) as the main raw material. It is mixed with human and animal manure to compost and decompose. It is mainly used for organic treatment. Rubbish. The principle is to use microorganisms to metabolize and decompose organic matter in garbage, to perform harmless treatment at high temperature, and to produce organic fertilizer.

Because of its composting materials and composting principle, its composition and properties are similar to manure, so it is also called artificial manure. The materials used to make compost can be roughly divided into two categories according to their properties:

The first category: basic materials. That is, substances that are not easily decomposed, such as various crop straws, weeds, fallen leaves, vines, peat, garbage, vegetable waste, kitchen waste, etc.

The second category: substances that promote decomposition. Generally it is a substance with high nitrogen content and high temperature fiber decomposition bacteria, such as human and animal dung, sewage, silkworm sand, old compost, plant ash, lime and so on.

The third category: Absorbent substances. Adding a small amount of peat, fine soil and a small amount of superphosphate or phosphate rock during the stacking process can prevent and reduce the volatilization of ammonia and improve the fertilizer efficiency of compost. The compost method can be simply divided into aerobic compost method and anaerobic compost method according to the production method. Aerobic compost is the aerobic bacteria that absorb, oxidize and decompose wastes. Microorganisms oxidize a part of the absorbed organic substances into simple inorganic substances through their own life activities, and at the same time release the activities that can be used for microbial growth. The energy required, and another part of the organic matter is synthesized into a new cytoplasm, which allows microorganisms to continue to grow and reproduce, producing more organisms. At the same time as the biochemical degradation of organic matter, it is accompanied by heat generation. Because the thermal energy will not be completely radiated to the environment during the composting process, the temperature of the composting material will inevitably increase, which will cause some microorganisms that are not resistant to high temperature to die. Bacteria multiply quickly. Eco-kinetics shows that the main role of aerobic decomposition is the large and active thermophilic bacteria.

The flora oxidizes and decomposes organic matter in the presence of a large number of oxygen molecules, and simultaneously releases a large amount of energy. Anaerobic composting is an anaerobic fermentation of organic wastes (including municipal waste, human and animal manure, plant straws, excess sludge from sewage treatment plants, etc.) under aeration conditions to produce organic fertilizers to make solid waste harmless the process of. The composting method is the same as the aerobic composting method, but there is no ventilation system in the heap, the temperature of the heap is low, and the time required for maturation and harmlessness is longer. However, the anaerobic composting method is simple and labor-saving, and can be used when there is no urgent need for fertilizer or labor stress. Compost is an organic fertilizer with rich nutrients and long and stable fertilizer effect. At the same time, it helps to promote the formation of solid particle structure in the soil. It can increase the ability of the soil to retain water, maintain heat, breathe, and retain fertilizer. It can also make up for the shortcomings of a single nutrient in chemical fertilizers and long-term single use of chemical fertilizers to reduce soil compaction, water retention, and fertilizer retention performance.

The compost method has low investment, simple technology, and organic matter can be reused as fertilizer to achieve resource recycling. The waste reduction is obvious, but the requirements for waste classification are high, and the odor generated during aerobic decomposition has a certain impact on the environment. High compost cost or poor quality will affect compost product sales.

The compost method is significantly different from the landfill method: the purpose of landfill is to bury the garbage from the groundwater, keep it dry and not in contact with the air, and it is difficult to decompose in large quantities. The purpose of the compost method is to make organic waste Harm.

Municipal solid waste incineration

Waste incineration is a traditional method of garbage disposal and has become one of the main methods of urban garbage disposal. After the garbage is treated by incineration, the garbage can be reduced, land is saved, and various pathogens can be eliminated. Modern waste incinerators are equipped with good soot purification devices, which can effectively reduce the pollution to the atmosphere.

Modern waste incineration achieves the purposes of volume reduction, weight reduction and resource utilization after full combustion at high temperature, which mainly includes three stages of drying, burning and burnout. Through the computer automatic control system and automatic combustion control system, the burning conditions of the waste in the furnace can be monitored and adjusted in real time, and the grate operating speed and the amount of combustion air can be adjusted in time to ensure that the waste treatment is always in a controllable state. The capacity reduction rate after waste incineration is very high, which can reduce the volume of waste by 80% to 90%, realize the capacity reduction and weight reduction of waste disposal, minimize the amount of land resources occupied by waste, and effectively use the waste generated by incineration. Thermal energy.

The advantages of waste incineration are:

After the garbage is incinerated, the pathogens in the garbage are completely eliminated, and the toxic and harmful gases and smoke and dust generated during the combustion process are discharged after the treatment meets the standards, and the degree of harmlessness is high.

After incineration, the combustible components in the garbage can be reduced by 80% to 90% after being decomposed at high temperature. The capacity reduction effect is good, which can save a lot of landfill land, and the waste incineration after separation is better.

Waste is used as energy. The high-temperature flue gas generated by waste incineration is converted into steam for heating and power generation, and resources such as ferromagnetic metals can be recovered to fully realize the recycling of waste treatment.

The area of the waste incineration plant is small, and the exhaust gas is less polluted after being purified.

The incineration process can be operated around the clock and is not easily affected by the weather.

However, after hundreds of years of practice, the waste incineration method has not been accepted by the general public. Its disadvantages are manifested in the aspects of heavier latent pollution, costly operations, complicated operations and waste of resources. Although its pollution prevention technology is improving day by day, it is still immature and cannot stand the test of theory and practice. At present, waste incineration has caused mass incidents and a large number of petitions and lawsuits ^[2] .