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According to the treatment medium, it can be divided into non-biological treatment and biological treatment: non-biological treatment includes mechanical crushing, sanitary landfill, incineration power generation, gasification and so on. Biological treatment includes anaerobic fermentation, aerobic fermentation and preparation of ecological feed.
(1) mechanical crushing. Make full use of the municipal sewage treatment system, and the domestic garbage will enter the municipal sewage system for treatment after being crushed by the garbage crusher. In the process of mechanical crushing, the kitchen waste did not change chemically, but the particle size became smaller. This method is essentially to sludge the kitchen waste sewage, not to digest it, but to transfer the waste. It is only suitable for cities or regions with new plans to accept this part of garbage treatment, otherwise it will inevitably pose a challenge to the original urban sewage treatment system.
(2) Sanitary landfill. Burying kitchen waste underground, including the process of organic matter being continuously degraded by microorganisms, is the sanitary landfill of kitchen waste. The biochemical treatment process of microorganisms is a research hotspot in recent years. The general conclusion is that microorganisms preferentially decompose organic matter and convert it into nutrients needed for their own growth and reproduction. In the case of excess organic matter, they can further degrade organic matter into inorganic matter to increase soil fertility.
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Sanitary landfill has the advantages of simple operation and low cost. At the same time, it occupies a large area and takes a long time. There is secondary pollution of leachate, which releases peculiar smell, and the by-product biogas is easy to cause explosion. With people's increasing attention to environmental problems and the increasing shortage of land resources, the sanitary landfill rate of kitchen waste has decreased year by year.
(3) Incineration for power generation. Because of its high water content, kitchen waste is not suitable for direct combustion, so it must be dehydrated first and then completely oxidized and decomposed in the incinerator. In general, when the temperature is not lower than 15%, the solids can be reduced by 65% (1000℃). The high-grade heat of combustion is generally used for power generation, and the low-grade heat can be used for heating. Ashes can be used as raw materials for building materials. In order to ensure the continuous and stable incineration process, 20% coal can be blended.
At present, garbage incineration technology is mainly divided into three categories: layered combustion, fluidized bed combustion and rotary combustion technology (namely rotary kiln).
The method has high treatment rate, the power steam generated by conversion is used for power generation, and the low-grade heat is used for heating, so that the reduction degree is great, and the recycling and reduction of kitchen waste are realized; However, conventional garbage incineration will inevitably produce furan, dioxin, fly ash and other air pollutants. In addition, the ash of incinerator (usually 5% ~ 20% before incineration) has a high content of heavy metals, which seriously pollutes the environment.
(4) Anaerobic fermentation. Anaerobic fermentation means that under anoxic or even anaerobic conditions, a part of organic matter is transformed into microorganisms by microorganisms, and the other part is decomposed into CH4 (some processes can be directly decomposed into H2) and CO2. Organic acids or alcohols can also be prepared by selecting different microorganisms. Temperature, pH, C/N ratio, trace elements and oxygen content significantly restrict the rate and conversion rate of anaerobic fermentation [3]. At present, anaerobic fermentation technology has made great progress in Europe, and the representative process in China is Biomax.
Centralized anaerobic fermentation technology is relatively mature, with a high degree of automation, which can produce fuel gas or organic acid and alcohol, with good resource utilization and high economy, and the residue can be made into organic fertilizer. It is widely used in the treatment of municipal solid waste and is an effective way to clean and recycle kitchen waste.
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(5) Aerobic fermentation. Aerobic composting of kitchen waste [1] refers to the process of biodegradation of kitchen waste by artificially cultured special bacteria or natural aerobic microorganisms under oxygen-enriched conditions. Similar to anaerobic fermentation, a part of organic matter is transformed into microorganisms, but different from anaerobic fermentation, on the other hand, it is transformed into organic fertilizer without producing CH4 or H2.
At present, the core technology of aerobic fermentation of kitchen waste mainly focuses on the optimization and domestication of aerobic microorganisms and the rationalization and improvement of reactors. Aerobic fermentation of kitchen waste mainly includes squeezing dehydration, oil-water separation, biochemical degradation, tail gas treatment, wastewater purification and organic fertilizer treatment. In the process of biochemical degradation, food waste with particle size of 1.5 ~ 8 cm is usually used as raw material, and strains and auxiliary materials are added for fermentation, and the fermentation time is about 4 weeks.
If the oil and salt of kitchen waste are too high, it will reduce the activity of microorganisms. In addition, centralized aerobic fermentation will occupy a large area, produce polluted odor and have low economic benefits. The number of harmless composting plants in China is decreasing year by year, which is related to the high cost of municipal waste mixing and sorting and the low economic benefit of composting enterprises.
What is worth recommending is the high-temperature aerobic rapid degradation technology, which uses efficient microbial flora to transform kitchen waste into organic fertilizer through aerobic fermentation 1 day. This method has the advantages of high speed, good salinity adaptability and high temperature activity (even up to 80℃). Compared with aerobic compost, the high-temperature aerobic reaction process does not produce any harmful substances, produces relatively less gas, consumes less time, is controllable, is simple to operate, has fast degradation, has good resource utilization effect, can treat mixed environmental-friendly garbage and has low operating cost. In addition, 90% of organic waste is discharged up to the standard, and oil is recovered in the pretreatment process of the former waste. 10% of solid emissions are used as organic fertilizer raw materials for ecological planting and breeding. The whole treatment process has no pollution and no secondary pollution. In line with the national principle of "reduction, harmlessness and resource utilization" in the treatment of kitchen waste. At present, the integrated kitchen waste equipment has been put into the market and has been popularized and applied.
(6) Preparing ecological feed. Ecological feed [1] refers to the feed prepared from kitchen waste. The treatment methods of preparing ecological feed from kitchen waste are mainly divided into three categories: fermentation to produce bacterial protein, silage and dehydration. Fermentation is widely used to prepare bacterial protein in China. The typical practice of silage method is lactic acid bacteria fermentation; Dehydration to prepare dry feed usually includes direct high temperature drying, boiling drying, vacuum frying and other methods.
(7) gasification. Although there are many mainstream gasification technologies in coal chemical industry and other fields, few gasification technologies can be applied to the treatment of kitchen waste stably, economically and reasonably because of its high water content. Only high temperature plasma torch gasification technology is recommended here [8]. This technology has the characteristics of fast reaction speed, high added value and environmental protection. The core technology is mastered abroad, mainly applied in the United States, Canada and Japan. Using this technology, the solid after simple dehydration can be gasified with oil. Due to the high temperature plasma gasification reaction and reasonable gas flow residence time, organic pollutants such as dioxins and furans are basically not produced, and the effective components of synthesis gas are CO and H2. Solid slag can be used as raw material for building insulation, but it has not been widely used in China at present, so it is necessary to introduce core technology.
2 conclusion
At present, the mainstream treatment method of abiotic kitchen waste in China is incineration power generation, and high temperature plasma torch gasification power generation technology is the most promising technology to replace incineration. Large-scale garbage gasification technology is still in the stage of popularization and application, and the market potential is huge.
Anaerobic fermentation and traditional aerobic composting can realize the recycling and reduction of kitchen waste. Generally speaking, the advantages of microbial treatment of kitchen waste are simple process, low initial investment, high degree of automation and little secondary pollution; Although it has some disadvantages, such as high energy consumption, small reduction degree, poor salinity adaptability, and often need to add auxiliary materials, it can be recycled and has a certain output. At present, the miniaturized integrated kitchen waste equipment, as a new waste solution, is widely used in government canteens, school canteens, hotels, restaurants, residential quarters, food processing plants, airports, street communities, large factories, agricultural products wholesale markets, fruit and vegetable production bases, food processing plants and so on.
Source: www.lbome.cn.