Agricultural waste, also called agricultural waste, mainly includes plant fiber waste (such as crop straw, chaff, husk, leaves, and bagasse, etc.), agricultural product processing waste, livestock and poultry manure, rural domestic waste, sewage, etc. It is huge and widely distributed. It is both a valuable renewable resource and a major source of environmental pollution in rural areas. The disposal of agricultural waste is of great significance to achieve cleanliness of the rural household environment, efficient use of resources, and harmless agricultural production, eliminate rural dirty, disorder, and poor, and promote the construction of a harmonious society and the construction of a new socialist countryside.

1. Agricultural waste treatment status

Crop straw is the largest by-product of agricultural production, and its total amount is 1.1 to 1.2 times the total grain output. China produces about 650 million tons of crop stalks each year, of which 15% is lost from fertilizing and returning to the field and collecting losses, 12% of industrial raw materials, 13% of feed, 25% of fuel, and about 50% is returned directly to the field, burned or throw away. In fact, crop straw is not only an important source of rural living fuel, livestock feed, and organic fertilizers, but also an important industrial and building raw material, so it should be fully utilized.

2. Analysis of agricultural waste treatment technology

There are many types of straw. Generally, straw can be divided into three categories: rice, wheat, rape, corn sorghum, and cotton sugar cane. The first type of rice, wheat, and rapeseed stalks are similar in nature and soft in texture. In general, they are mainly used in two effective ways: direct return to the field and collection and utilization. Biogas can also be prepared after pretreatment; the second type of corn is highly dyed and green. The stalk has a high sugar content and is suitable as a silage. The stalk can be used as a gasification fuel; the third type of cotton stalk and bagasse have high lignin content and are suitable for forming carbonization and gasification.

In view of the above analysis, the utilization of straw has broad prospects, and it is necessary to conduct in-depth research on relevant key technologies and processes. It is also necessary to concurrently correlate relevant equipment or equipment and combine the specific characteristics of straw characteristics, regional planting system, and regional energy structure, etc. Comprehensive straw utilization program. According to the classification of straw, corresponding straw treatment methods were proposed, and the application characteristics and development trends of various technologies were analyzed.

3. Development of supporting agricultural machinery

In the comprehensive utilization of agricultural waste, the development of corresponding supporting agricultural machinery is also needed as a support. With the development of multi-channel resource utilization of agricultural waste, more and more requirements have been put forward for the development of corresponding agricultural machinery supporting equipment and equipment.

Supporting agricultural machinery for straw treatment

For straws that can be returned directly to the field, such as rice, wheat, and rapeseed, it is necessary to vigorously develop and promote straw pulverizers or direct burial machines. After the field straw is crushed on the ground and evenly scattered on the ground, it is then burrowed by ploughing. Currently, most tractors are used to directly crush the straw to return to the field. For the straw that can be decomposed without crushing, the straw can be directly buried in the soil through a machine that integrates land preparation and burial, which is also a method suitable for the south.

For straw that is not suitable for direct return to the field, it should be collected and used as much as possible first. It is required to use a semi-feeding harvester to completely save the straw and keep the stubble low, which will facilitate the subsequent use. At present, semi-feed harvesters are more expensive than full-feed harvesters and require further government promotion. For straw utilization methods such as gasification, biogas production, and molding, the straw needs to be pulverized in advance. Therefore, a demand for a straw pulverizer has been formed, which not only requires that various straws can be pulverized to the required length or particle size. For biogas production, it is also required to be able to effectively destroy the waxy layer on the surface of the straw to facilitate full degradation. Especially soft straws are prone to entanglement and other faults during crushing. The development and promotion of such machines should be further increased.

Straw gasification is a rapid development method in recent years. The core component of straw gasification lies in the straw gasification furnace. It is necessary to concentrate technical efforts to solve problems such as tar and fuel adaption surface, and promote the application of gasification furnaces.

Mechanism charcoal is a straw forming method. For biomass extrusion molding equipment, the problems that need to be solved are mainly to improve the reliability of the equipment unit, especially to increase the service life of the wear parts. In addition, it is necessary to expand the scope of equipment adaptation and improve the economic efficiency of the equipment.

In the next 15 to 20 years, the total amount of agricultural waste production will continue to increase. Without proper use and treatment, agricultural waste, especially livestock and poultry farming, will pollute the environment more seriously. The disposal of agricultural waste is not only related to the reuse of resources and environmental safety, but also is closely related to the sustainable development of agriculture and the construction of a rural “two-oriented” society.

In the field of agricultural waste treatment, we should vigorously adopt modern biotechnology and process technology to improve the level of agricultural waste treatment and improve the utilization rate of waste. While treating agricultural waste, we must eliminate the pollution of agricultural waste to the environment and develop health. Material economy, development of material energy, development of ecological circular agriculture, and promotion of rural economic and social development.

Biomass refers to various organisms produced through photosynthesis using the atmosphere, water, land, etc., that is, all living organic matter that can grow is collectively called biomass. It includes plants, animals and microorganisms. Broad concept: Biomass includes all plants and microorganisms, as well as animals and food wastes produced by plants and microorganisms. Representative biomass such as crops, crop waste, wood, wood waste and animal waste. Narrow concept: Biomass mainly refers to lignocellulose (such as lignin) in the agricultural and forestry production process, except for grain and fruits, straws, trees, etc., agricultural industry waste, agricultural and forestry waste, and poultry in the production process of livestock. Animal manure and waste. Features: renewable, low pollution, widely distributed.

According to different sources, biomass suitable for energy use can be divided into five categories: forestry resources, agricultural resources, domestic sewage and industrial organic wastewater, municipal solid waste, and livestock and poultry manure.

Forestry biomass resources refer to the biomass provided by forest growth and forestry production processes, including fuelwood forests, non-educational wood in forest tending and thinning operations, residual branches, leaves and sawdust, etc .; during wood harvesting and processing Branches, sawdust, wood layers, tips, slabs and carriers; wastes from forestry by-products, such as shells and kernels.

Agricultural biomass resources refer to agricultural crops (including energy crops); wastes from agricultural production processes, such as crop straws (corn straw, sorghum straw, wheat straw, straw, bean straw and cotton straw) Etc.); waste from the agricultural processing industry, such as rice husks left over from agricultural production. Energy plants broadly refer to a variety of plants used to provide energy, usually including herbaceous energy crops, oil crops, hydrocarbon-producing plants and aquatic plants.

Domestic sewage is mainly composed of various drainages from urban residents’ living, business and service industries, such as cooling water, bath drainage, toilet drainage, laundry drainage, kitchen drainage, and fecal sewage. Industrial organic wastewater is mainly wastewater discharged during the production process of alcohol, brewing, power, food, pharmaceutical, papermaking and slaughtering industries, etc., which are rich in organic matter.

Municipal solid waste is mainly composed of solid waste such as urban household solid waste, commercial and service waste, and a small amount of construction waste. Its composition is relatively complicated and is affected by factors such as the average living standard of local residents, energy consumption structure, urban construction, natural conditions, traditional habits, and seasonal changes.

Livestock and poultry manure is a general term for livestock and poultry excreta. It is a transformed form of other forms of biomass (mainly grain, crop straws and pastures, etc.), including manure, urine and its mixture with bedding. Biogas is a kind of combustible gas converted from biomass energy, which can usually be used by farmers for cooking and lighting.

The harm of rural solid waste
1. Polluted water source
If the solid waste flows into the local rivers and lakes, it will often bring a lot of harmful substances in the waste into the water body, which will do harm to the growth of various aquatic animals and plants, and also cause pollution to the water source; the seepage liquid generated by the solid waste accumulation is more serious, it will penetrate into the underground water through the soil, polluting people’s drinking and domestic water. In addition, a large number of aerobic putrefactive organic material flows into the river will often make the water eutrophication, lead to the crazy growth of some microorganisms, resulting in the imbalance of biological structure; and some wastes such as straw directly thrown into the river will often lead to river blockage. The polluted atmosphere often contains a large amount of fly ash in the solid waste, and these fly ash and the small dust particles in the waste will often diffuse into the atmosphere; some organic solid waste will degrade and form biogas under the condition of appropriate humidity, which will have a great impact on the growth of nearby plants, and some specific chemical toxic waste will also under certain conditions In chemical reaction, the resulting toxic gas diffuses into the atmosphere with the wind, which poses a threat to the health of nearby residents. At last, a large number of smoke and harmful gases will be produced when burning it in memory, which will seriously affect the air quality in rural areas.
1.1 polluted land
If we don’t treat solid waste in a unified and scientific way and let it accumulate, after a long period of sun and rain, the toxic liquid produced by it will permeate into the soil, causing damage to the soil. Many wastes that are difficult to be classified by nature in a short period of time will remain in the soil for a long time, seriously affecting the structure and function of the land, and even killing the micro in the soil At present, many farmers are used to burning straw,
The formation of high temperature by incineration will do great harm to the surface microorganisms, which will reduce the fertility of the soil and destroy the balance of the biological system in the soil.
2. Treatment of rural solid waste
2.1 composting treatment
For the organic solid waste, we often go to the composting treatment method, which refers to the artificial control of the solid waste stacking environment, under certain temperature, humidity and ventilation conditions, the use of bacteria and fungi for fermentation, composting is a kind of artificial decomposition method. Compost is usually a loose brown substance with soil texture. It looks like humus soil. Therefore, some people call it humus soil. Compost is a very good soil conditioner, which is usually used for straw or livestock waste.
2.2 centralized Incineration
It has been used for a hundred years to concentrate solid waste for unified incineration treatment, and there is a great development in both incineration means and incineration equipment. The incineration here refers to the concentration of solid waste into the incinerator to burn completely, and then use some equipment to convert the energy released in the combustion process into electrical energy. The smoke generated in the incineration process can be discharged after purification and treatment, and the residue after incineration can be used in other places. The incineration capacity of rural solid waste is relatively large, and the secondary utilization of the waste can be realized through the electric energy generated by the incineration of solid waste. Centralized incineration is one of the most commonly used methods in the treatment of rural solid waste in China, which also exists in many foreign countries. However, it must be noted that some areas with poor equipment conditions will pollute the atmosphere if they cannot effectively purify the incineration flue gas.
2.3. Landfill
The landfill technology of rural solid waste is relatively simple, and its cost is lower. The general process of landfill treatment mainly includes classifying solid wastes and sending them to the conveyor. Before this step, try to clean up the wastes that can be reused, such as waste paper and plastic, and transport the wastes of different sizes and types to different machines, dry and grind the mail wastes after fermentation, and then put these wastes into the conveyor The fertilizer of the machine is well packed; after other wastes are crushed and ground, they are mixed with clay to make hollow bricks for reuse.

Definition of hazardous waste
According to the law of the people’s Republic of China on the prevention and control of environmental pollution by solid waste and the measures for the administration of hazardous waste business license, hazardous waste refers to the solid waste with hazardous characteristics identified in the list of wastes or in accordance with the identification standards and methods for hazardous waste specified by the state.
The definition includes two meanings: one is that hazardous waste belongs to a part of solid waste (in other words, a substance that does not belong to solid waste must not belong to hazardous waste); the other is that hazardous waste must have hazardous characteristics. There are five common characteristics of hazardous waste, which are toxicity (including leaching toxicity and biological toxicity), corrosiveness, flammability and infection The solid waste with one or more hazardous characteristics is hazardous waste.
Industrial Enterprises
1. Mine tailings and mine solid waste:
It belongs to solid waste and does not belong to hazardous waste. According to: guidelines for declaration and registration of solid waste discharge and item 21 of list of industrial solid waste, the mine belongs to general industrial solid waste, and belongs to category I of general industrial solid waste, and the treatment and disposal method should give priority to mining pit and collapse area for backfilling.
In part 6 of the new version of the standard for the identification of solid wastes – General principles (gb34330-2017), it is clearly proposed that the mining waste, tailings and coal gangue in the mined out areas of metal mines, non-metal mines and coal mining and beneficiation that meet the class I general solid wastes in gb18599 shall not be managed as solid wastes, so they are also hazardous wastes.
If the mine solid waste is mixed with other hazardous wastes, its hazardous characteristics sometimes need to be determined according to the identification standard of hazardous wastes; another kind of cyanide tailing and cyanide sludge produced in the process of gold mining (this process has been listed in the process banned and eliminated by the state) are hazardous wastes.
2. Paper white mud and carbide slag:
It belongs to solid waste and does not belong to hazardous waste. According to the guidance for declaration and registration of solid waste discharge and item 3 of the list of industrial solid waste, carbide slag is a calcium containing solid waste, mainly composed of calcium hydroxide, which belongs to general industrial solid waste, and the first process of general industrial solid waste can be added and used by water sludge Enterprises, and can also be put into a special industrial solid waste landfill for landfill treatment 。 Carbide slag is the leading enterprise in the application of flue gas desulfurization.
3. Natural gas purification desulfurizer and desulfurization gypsum:
It belongs to solid waste and does not belong to hazardous waste. The main component of natural gas desulfurizer is iron oxide, which does not have hazardous characteristics and is not included in the national records (2016). However, natural gas desulfurizer often contains sulfur dioxide or other organic components. Some provinces and cities will improve the management level by referring to hazardous waste in the management process.
The final components of ordinary FGD agent and FGD gypsum are mainly calcium sulfate, which are not hazardous wastes. If desulfurizer and desulfurized gypsum are mixed (such as heavy metal and incineration fly ash), they shall be managed according to the principle of hazardous waste mixing (the same below).
4. Antibiotic dregs (including the vast majority of traditional Chinese medicine residues):
It belongs to the category of solid waste and does not belong to hazardous waste. According to Article 23 of the regulations on the administration of narcotic drugs and psychotropic substances (Order No. 442 of the State Council) and the measures for the administration of the production of psychotropic substances (for Trial Implementation) (gsyja [2005] No. 528), the active liquid produced in the production shall be destroyed and recorded by the enterprise itself. In the list of industrial solid wastes, the residues of traditional Chinese medicine belong to the 15th category of wastes in the list.
What needs to be treated differently is: the waste mother liquor, distillation residue or reaction residue generated in the purification or chemical reaction process of API belong to the hazardous substance category of medical waste HW02.
5. Water based mud:
It belongs to solid waste and does not belong to hazardous waste. In the list of national hazardous wastes (2016 Edition), for the drilling mud prepared continuously in the oil and natural gas exploitation industry, the waste drilling mud, oil sludge oil foot, oil-based rock cuttings and oil containing mud finally generated belong to the hazardous waste hw08, with the waste codes of 071-001 (or 002) – 08 and 072-001-08 respectively.
In the 2016 edition of the national list of hazardous wastes, there is no reference to the waste problem of preparing drilling mud with water-based continuous phase, that is, the water-based mud record, so it does not belong to the category of hazardous waste.

6. Coal tar from coal to gas and coal tar from coke production enterprises:
According to the current national list of hazardous wastes (2016 Edition), the coal to gas industry (water gas generator) and gas purification (including condensation) process oil residue belong to hw11 type hazardous wastes. If the coal tar produced by coke production industry fails to meet the requirements of coal tar standard (Yb / t5075-2010). In addition, coal tar is produced in the process of gas production during condensation. If the coal tar standard (Yb / t5075-2010) is met, naphthalene, anthracene oil and wash oil will be used for exemption from management (please note: only the utilization process is not included in the management of hazardous waste, but collection, storage, transportation and treatment of hazardous waste are not exempted).
It is analyzed that the coal tar produced in the coke production process should be classified as hazardous waste, because the acid tar and other tar (hw252-011-11) produced in the special production process of the national list of hazardous wastes (2016 version) are hazardous waste, and the “other tar” should include coal tar. If there is a mistake in the explanation, other tar should be understood as tar and benzene (or benzene series) containing substances that can not meet the coal tar standard (Yb / t5075-2010). If “other tar” directly includes coal tar, the list does not need to be specifically expressed as other tar. In the process of management, coal tar that has passed the environmental assessment and meets the product quality requirements cannot be easily identified as hazardous waste.
7. Electroplating wastewater and sludge with heavy metals exceeding the standard:
Electroplating sludge is a kind of hazardous waste, and the waste types often belong to hw17, hw21, hw22 and hw23 at the same time. The prevention and control scope of electroplating waste pollution with heavy metals exceeding the standard is included in the waste water management, which is not applicable to the scope of the law of the people’s Republic of China on the prevention and control of environmental pollution by solid wastes, and is not included in the hazardous waste management. However, according to the two high judicial interpretations (2016 version), if the class I heavy metals (such as lead, mercury, chromium, cadmium, or class II heavy metals (such as nickel Copper, zinc, manganese and vanadium) exceeding the standard by more than 10 times shall be prosecuted for criminal responsibility in addition to administrative penalty.
8. Aluminum ash produced in pyrometallurgy:
It belongs to solid waste and does not belong to hazardous waste. The aluminum ash produced in the process of pyrometallurgy can often be directly mixed into the smelting furnace. According to the fifth part of the guidelines for identification of substances – General principles (gb34330-2017), if it is directly returned to the original production process, it belongs to the production raw materials, and the hazardous wastes not produced by solid mainly include the skimming slag or primary smelting slag (fluorine exceeds the standard) produced by pyrometallurgy process, and the generated by electrolysis process The code of salt slag, dross or electrolytic cell is 321-022 (023-026) – 48 respectively.

China’s large-scale construction of sewage and water treatment plants, but sludge treatment and disposal has been neglected. The biggest bottleneck of sludge disposal is drying reduction. High cost has always been a problem that plagued the industry. In recent years, the sewage sludge drying technology has developed rapidly. The working principle and process of the direct heating drum sludge drying technology are introduced below.

First, the working principle of direct heating drum sludge drying technology:

The dewatered sludge enters the mixer from the sludge funnel, and a part of the sludge that has been dried is thoroughly mixed in proportion to make the solid content of the wet and dry mixed sludge reach 50% to 60%, and then transported to the screw conveyor. Three-channel drum dryer.

Second, the process of direct heating drum sludge drying technology:

In the drum, it comes into contact with the hot air flow with a flow rate of 1.2-1.3m / s and a temperature of about 700 ° C, which is mixed into the drum, and heated in a concentrated manner. After about 25 minutes of treatment, the dried sludge is conveyed by a screw with a metering device. The machine is sent to the separator, and the humid and hot gas discharged from the dryer is collected for thermal recycling, and the foul gas with pollution is sent to the biological filter for treatment to meet the discharge standards that meet environmental protection requirements. The granularity of the sludge can be controlled, and then the sludge particles that meet the requirements are sent to a storage bin for treatment through a filter.

The dryness of the dried sludge is above 92% or higher. The diameter of dried sludge particles can be controlled at 1-4mm, which mainly considers the possibility of using dried sludge as fertilizer or landscaping. The fine dry sludge is sent to the mixer and mixed with the wet sludge into the drum dryer. The burner used to heat the drum dryer can use biogas, natural gas or hot oil as fuel.

The separator separates the dried sludge from water vapor. The water vapor carries almost all the heat consumed by the sludge during drying, and this part of the heat needs to be fully recycled. Therefore, water vapor must pass through the condenser, the cooling water inlet temperature of the condenser is 20 ° C, and the outlet water temperature is 55 ° C. The cooled gas is sent to the biofilter for treatment, and the exhaust gas is discharged after it has completely reached the discharge standard.

The characteristics of the drying system are: operating in an oxygen-free environment, no dust is generated, the dried sludge is granular, the particle size can be controlled, and the gas recycling design is used to reduce the cost of tail gas treatment.