Kitchen waste, commonly known as sewage sludge, is a kind of domestic waste formed by residents in the daily consumption process, which is easy to rot and stink and spread bacteria and viruses. The main components of kitchen waste include rice and flour food residues, vegetables, animal and vegetable oils, meat and bones. From the chemical composition, there are starch, cellulose, protein, lipids and inorganic salts.
1. process flow
2. Technical indicators
3. Process characteristics
brief introduction
The main characteristics of kitchen waste are rich in organic matter, high water content, perishable, and its properties and odor will
Kitchen garbage disposal
It has a bad influence on environmental sanitation and is easy to breed harmful substances such as pathogenic microorganisms and mycotoxins.
One minute it's delicious food, and the next minute it's garbage. Due to food culture and eating habits, kitchen waste has become a unique phenomenon in China. The table garbage in China is amazing, and a huge amount of kitchen garbage is produced every day. According to the data of beijing municipal commission of development and reform, Beijing produces 65,438+0,200 tons of kitchen waste every day. According to the statistics of Tsinghua University Institute of Solid Waste Pollution Control and Recycling, China produces no less than 60 million tons of kitchen waste every year.
Experts believe that nutritious kitchen waste is a valuable renewable resource. However, due to lack of attention and improper disposal methods, it has become a potential source of danger affecting food safety and ecological safety. Although improper disposal will have serious consequences, kitchen waste is not without its merits. He Bingguang, deputy director of the Environmental Protection Department of the National Development and Reform Commission, pointed out that kitchen waste has the dual characteristics of waste and resources, which can be said to be a typical "dislocation of local resources". [ 1]
classify
According to different sources, kitchen waste is mainly divided into catering waste and kitchen waste. The former is produced by the leftovers of restaurants, canteens and other restaurants, which has the characteristics of large quantity, many sources and wide distribution. The latter mainly refers to the leftovers discarded by residents during daily cooking, and the quantity is not as large as that of food waste.
harm
For a long time in the past, there was no management regulation specifically for kitchen waste in China. Some kitchen waste is fed to pigs without treatment, or recycled and refined by illegal traders, or buried with ordinary domestic waste.
Food waste is perishable.
However, feeding pigs with untreated kitchen waste can easily lead to the spread of diseases. Nie Yongfeng, director of the Institute of Solid Waste Pollution Control and Resource Utilization of the Department of Environment of Tsinghua University, pointed out that the kitchen waste produced by the catering industry may contain many kinds of germs. If livestock and poultry are directly raised without treatment, it will bring harm to human health through the accumulation of toxins and harmful substances in livestock and poultry, thus causing cross-infection between humans and animals. Therefore, this form of food chain hides the great danger of pathogen transfer and diffusion. The United States, Canada, the European Union and many other countries have enacted many laws prohibiting the direct feeding of untreated kitchen waste to pigs.
Experts pointed out that "gutter oil" contains aflatoxin, benzene and other toxic substances. If it is returned to people's table through illegal channels, it will cause chronic diseases and even cancer, which is extremely harmful to people's health.
Zhang Yuhua, a researcher at the Institute of Energy and Environmental Protection of the Planning and Design Institute of the Ministry of Agriculture, pointed out that because kitchen waste is very perishable, it will produce unacceptable bad feelings, such as pungent odor. However, the kitchen waste produced by catering industry contains a lot of leftover soup and spoiled water, which is easy to leak during collection and transportation and affects the urban environment. Direct landfill treatment of kitchen waste will cause serious pollution to groundwater. [ 1]
resources
According to the estimation of experts from the Ministry of Agriculture, kitchen waste contains a lot of nutrients, and the main components are oil and protein.
kitchen waste
Instead of corn, fish meal and soybean meal, it can be processed into high-energy protein high-quality feed and is also a suitable raw material for producing biodiesel.
Experts explained that according to the dry matter content, 50 million tons of kitchen waste is equivalent to 5 million tons of high-quality feed, and the energy contained is equivalent to the energy output of 6.5438 million mu of cultivated land every year, and the protein contained is equivalent to the protein output of 20 million mu of soybeans every year. In other words, if all the kitchen waste produced in China in one year is used, it is equivalent to saving about 6.5438+million mu of cultivated land.
He Bingguang pointed out that in the face of the shortage of cultivated land and grain in China, a large amount of grain and feed needs to be imported every year. Reasonable utilization of kitchen waste is an effective way to improve the utilization rate of resources and solve the food problem in China to some extent. Moreover, this utilization conforms to the characteristics of reduction, reuse and resource utilization, and is a vivid case of developing circular economy. [ 1]
Utilization method
The main feeding techniques of kitchen waste are biological method and physical method.
biological method
Recycling of kitchen waste
The biological method uses microbial fermentation technology to produce fermented feed, which generally takes a long period and requires strain selection and management, which is more complicated. In 2002, China invented the patent CN02 1554 17. X applied by Chen Jianle discloses a method for producing high-calcium multi-dimensional yeast protein feed by using kitchen waste. The kitchen waste and swill raw materials which are crushed, dehydrated, neutralized and sterilized by a crusher are mixed, inoculated with yeast and microbial strains, mixed and controlled by a flow controller, and then solid fermentation is carried out in batches under the control of a computer, followed by drying, crushing, inspection and packaging.
physical law
The physical method is to dehydrate, dry and disinfect the kitchen waste, and make it into dry feed after crushing. China invention patent CN98 103203.6 applied by Zhang Zai 1998 discloses a method for recycling kitchen waste into livestock feed or agricultural organic fertilizer. The collected kitchen waste can be directly made into semi-finished products in one operation, and then sent to a batch of waiting tanks after source classification, crushing, formula measurement and dehydration, and then sent to a horizontal stirring tank for cooking, sterilization, fermentation or drying. When it is used to make feed, the kitchen waste mixed according to the formula in the metering barrel is sent to a horizontal stirring tank, stirred, cooked and sterilized at the temperature of 100℃ ~ 150℃, and then sent to a dehydrator for dehydration to a proper water content and then sent to a tank to be prepared; Then, that dehydrate kitchen waste is sent to a horizontal stirring tank through a batch of wait tanks, stirred and dried at the temperature of120 DEG C-150 DEG C, and a prop amount of grease and other nutrients are metered in from the grease storage tank and the additive storage tank according to the formula until the moisture drops to the specification requirements, so as to prepare a semi-finished product, and the semi-finished product is sent to a feed storage tank; Finally, the semi-finished products are made into granular or powdery fish, poultry and livestock feed or agricultural organic fertilizer by granulator or pulverizer as needed.
Policy action
Treatment of kitchen waste
Some large and medium-sized cities in China have begun to try to recycle kitchen waste. After exploration, it was initially formed.
Establish a technical evaluation mechanism for kitchen waste disposal.
The resource utilization modes of kitchen waste such as Ningbo mode, Shanghai mode and Xining mode were introduced. Because kitchen waste treatment is a public welfare project involving people's livelihood, although the specific operation modes of several modes are different, the same feature is that the government plays a leading role.
After more than ten cities such as Beijing, Shanghai, Suzhou, Ningbo, Chongqing and Xining introduced corresponding management measures, the technical standards for kitchen waste such as "gutter oil" have been formulated, and the national regulations on the management of kitchen waste will also be introduced in due course.
165438+20091On the morning of October 26th, the compilation of "Technical Standard for Recycling and Deep Processing of Waste Oil Resources from Kitchen" was started in the School of Chemistry and Environmental Engineering, Beijing Technology and Business University. This is the second national standard for kitchen waste in China.
Previously, the first national standard of kitchen waste, Technical Requirements for Resource Utilization of Kitchen Waste, was submitted to the State Council for approval. This will end the situation that there is no rule to follow in the recovery of "waste oil", and together with the planned national regulations on the management of kitchen waste, gradually establish a policy system for the harmless and resource-based utilization of kitchen waste.
Real effect
Ningbo made full use of the kitchen waste treatment technology independently developed by Ningbo Kaicheng Ecological Technology Co., Ltd., and the government issued the Measures for the Management of Kitchen Waste in Ningbo, and signed collection and transportation contracts with 20 10 kitchen waste generating units, with a signing rate of 72%. Garbage disposal and products are operated by Kaicheng Company in the market. In Kaicheng Company, vegetable soup and rice with bad smell were sorted, squeezed, dried and fermented to make microbial compound feed for livestock and poultry, and industrial oil was also extracted, which can be used to produce soap. Through cooperation with Tsinghua University, Zhejiang University and other institutions of higher learning, Kaicheng Company has deeply tapped the potential of comprehensive utilization of kitchen waste and strived to achieve "zero surplus" in kitchen waste treatment. According to Tao, deputy director of Ningbo Development and Reform Commission, from 2006 to 2009, Ningbo collected and transported 77,000 tons of kitchen waste, 5,200 tons of feed raw materials and 0/.800 tons of unsaturated lubricant. [ 1]
Method for treating kitchen waste
1. Making feed
At present, most of the kitchen waste in China is directly used as feed, and a few are used as feed through fermentation.
2. Landfill
A small part of domestic garbage is buried.
Make fertilizer
There is also a small amount of aerobic treatment as fertilizer.
4. Anaerobic treatment
Few people produce biogas through anaerobic fermentation.
Because kitchen waste contains all kinds of animal meat, if it is used as feed, cannibalism can easily lead to foot-and-mouth disease and various diseases, which will infect human beings and cause harm; Because of the high water content in landfill, it is easy to produce a lot of leachate and pollute groundwater; When making fertilizer, the smell is overflowing in the production process, which affects the surrounding environment; Anaerobic treatment can produce a lot of biogas. Biogas is a clean and renewable energy, which can be used for power generation and fuel. Because the system is completely closed and has no odor, anaerobic treatment of kitchen waste is the future development direction.
Introduction of anaerobic treatment technology of kitchen waste
1. process flow
The collected kitchen waste is removed by a sorting device, and then the oil is extracted to recover the oil, then it is pulped and tempered, and then it enters an anaerobic reaction tank, where it contacts with strains, and under the condition of a certain pH and C/N ratio, it is hydrolyzed, acidified and methanated to generate biogas, which is purified to generate electricity or directly make fuel. Biogas slurry is used as liquid fertilizer or discharged after aeration. A small amount of biogas residue is made into solid fertilizer by composting.
2. Technical indicators
(1) Gas production rate: 0.65-0.75m3/kg? Vs(2) Volume gas production rate: 2.0-2.50m3/m3? D (3) conversion rate: 85-90%
3. Process characteristics
(1) simple process, short process and low energy consumption. (2) fully enclosed operation, no peculiar smell during treatment. (3) The resource utilization rate is high, and the organic matter conversion rate reaches 85% or even more than 90%. (4) The biogas output is high, and each ton of kitchen waste can produce biogas 120 cubic meters or more. (5) The methane content in biogas is high, which can reach 60-75%.