Due to the limited kitchen space, on-site reduction treatment is the basic foothold of kitchen waste treatment. At present, many countries adopt the way of setting kitchen waste treatment device in the kitchen, and the crushed kitchen waste is discharged into the municipal drainage pipe network, mixed with water, and then put into the municipal sewage treatment system for harmless treatment, so as to achieve the purpose of harmlessness [1 1]. This method is suitable for units that produce less kitchen waste. However, this method often breeds germs, mosquitoes and flies in urban sewers, leading to the spread of diseases. At the same time, it may cause the blockage of drainage pipes, reduce the drainage capacity of urban sewers, increase the load of urban sewage treatment systems, and inevitably produce certain secondary pollution.
2 Landfill site
In many areas of our country, kitchen waste and ordinary waste are sent to landfills for landfill treatment. Landfill is the main treatment method for harmless treatment of domestic waste in most countries. Because kitchen waste contains a large number of degradable components, its stability time is short, which is beneficial to the recycling of landfill, and its operation is simple, so it is widely used [12]. With the more and more extensive understanding of the availability of kitchen waste, the landfill rate of kitchen waste in Europe, America, Japan and China is declining, and even many countries have banned kitchen waste from entering landfills for treatment [13].
3 fertilization treatment
The fertilization treatment methods of kitchen waste mainly include aerobic composting and anaerobic digestion. Aerobic composting process is that extracellular enzymes secreted by aerobic microorganisms decompose organic solids into soluble organic substances, and then penetrate into cells, and the whole composting process is realized through microbial metabolism [14]. At the same time, aerobic composting has also derived some similar methods, such as earthworm composting, which is a new technology developed in recent years. Earthworms are used to swallow a large amount of kitchen waste and mix it with soil. Through mechanical grinding and biochemical action in the intestine, the organic matter is transformed into nutrients that can be used by themselves or other organisms [15, 16]. Anaerobic digestion of kitchen waste refers to the decomposition of organic waste by microorganisms under specific anaerobic conditions, in which carbon, hydrogen and oxygen are converted into methane and carbon dioxide, while elements such as nitrogen, phosphorus and potassium remain in the residue and are converted into forms that are easily absorbed and utilized by animals and plants [17]. The disadvantage of kitchen waste composting is that the quality of fertilizer is not high, and the cost of composting with high quality is relatively high, which is difficult to popularize.
4 feed treatment
The principle of feed treatment of kitchen waste is to use a large amount of organic matter contained in kitchen waste to convert it into high-calorie animal feed after crushing, dehydration, fermentation and soft-hard separation, so as to turn waste into treasure. At present, the feed treatment technology of kitchen waste in China is mature, and many types of treatment technologies have been popularized in Shanghai, Beijing, Wuhan, Jinan and other cities. Fermentation is the most important step in feed processing, and many researches in this field have achieved remarkable results. Wu Suhuan [18] and others screened out Candida F- 1 and Aspergillus oryzae F-6 through mixed fermentation of various yeasts and molds. Under certain fermentation conditions, the crude protein content of the final feed was 33.87%, which was 6.85% higher than that of the raw material. Chen Jinzhong [19] and others used multi-strain mixed fermentation to treat trotters and straws at the same time. Under the conditions of 3∶ 1 mixing, 150℃ and high temperature, damp heat and acid treatment, crude protein >: 25%, crude fiber < 18% and moisture can be obtained.
5 energy treatment
The energy treatment of kitchen waste has risen rapidly in recent years, mainly including incineration, thermal decomposition and fermentation to produce hydrogen. Incineration treatment of kitchen waste has high efficiency, and finally produces about 5% residue, which is convenient for disposal. Incineration is carried out in a special incinerator, and the generated heat energy can be converted into steam or electric energy, thus realizing the recycling of energy. However, kitchen waste has high moisture content and low calorific value, and auxiliary fuel needs to be added during combustion, which leads to a big investment problem and tail gas treatment is also a difficult problem. Thermal decomposition method is to pyrolyze garbage at high temperature, so that the energy contained in garbage can be converted into gas, oil and carbon, and then used. Thermal decomposition method has broad application prospects, but this technology has not yet reached the practical stage and is rarely used at present. As a high-quality clean energy, hydrogen is generally considered as the most potential alternative energy. Many scholars have studied this. Layjimm-JYI [20] et al. obtained microorganisms from activated sludge and conducted hydrogen production experiments on kitchen waste with different chemical components. The conclusion is that the hydrogen production capacity of sugar waste is about 20 times that of ester and protein waste, and Liu Min [2 1] and Zhao Chunfang [20] will pay more and more attention to the energy treatment of kitchen waste.
6 others
Using edible waste oil to vacuum fry kitchen waste can achieve the purpose of treating kitchen waste and edible waste oil at the same time, which can not only quickly remove water from kitchen waste, but also greatly reduce the oxidation speed of fried food, which not only ensures the nutritional components of waste, but also can be disinfected in vacuum once. Fried food can be used as an ideal green feed. Extraction of biodegradable plastics technology, 1999 Japanese scholar Shirai put forward the technology of producing lactic acid by fermentation of kitchen waste and then synthesizing polylactic acid, which opened up a new way for resource utilization of kitchen waste and reducing the production cost of lactic acid [23]. Lactic acid fermentation of kitchen waste can solve the problems of large discharge and difficult treatment of municipal waste, and the environmental pollution caused by it. At the same time, the prepared biodegradable plastics are expected to become substitutes for general plastics.