In recent years, China has issued a series of policies and measures to promote the development of sludge disposal industry. Among them, proper disposal of sludge, effective utilization of resources in sludge, improvement of disposal efficiency and reduction of disposal cost have become the focus of the industry.
Sludge drying: the process of removing most of the water content from sludge through infiltration or evaporation. Generally, it refers to the use of self evaporation facilities such as sludge drying field (bed) or drying facilities using heat sources such as steam, flue gas and hot oil.
Sludge incineration: a process of sludge disposal. It uses an incinerator to heat and dry the dewatered sludge, and then oxidizes the organic matter in the sludge at high temperature to make the sludge become a small amount of ash.
Sludge classification: it belongs to coarse-grained hydrophobic inorganic sludge with good compressibility and dewatering performance
1. General technology of sludge treatment and utilization
(1) sludge composting treatment technology
(2) building material technology of sludge
(3) fuel technology of sludge
(4) anaerobic digestion (biogas production) technology of sludge
2. Solar sludge drying technology
3. Ionizing radiation treatment technology of sludge
4. Application of microwave technology in sludge treatment
(1) microwave irradiation sludge treatment technology
⑵ microwave chemical analysis technology
5. Ultrasonic sludge treatment technology
⒍ bioavailability of heavy metals and plant removal technology
7 microbial treatment technology of sludge
(3) microbial deodorization technology
(1) wet oxidation technology
(2) activated sludge as binder
(3) preparation of degradable plastics from surplus sludge
(4) preparation of activated carbon from sludge
(5) O3 / H2O2 oxidation technology
(6) UV / O3 oxidation technology
(7) UV / H2O2 oxidation process
(8) introduction to other thermochemical treatment technologies
This treatment method is simple, easy, low cost, sludge does not need high dehydration, and has strong adaptability. However, there are also some problems in sludge landfill, especially the formation of landfill leachate and gas. Leachate is a kind of seriously polluted liquid. If the landfill site is selected or operated improperly, it will pollute the groundwater environment. The gas produced by landfill site is mainly methane, which will cause explosion and combustion if appropriate measures are not taken.
Due to the advantages of low investment, low energy consumption, low operation cost and the organic part can be transformed into soil conditioner, the direct land use of sludge is considered to be a disposal method with development potential. Scientific and reasonable land use can reduce the negative effects brought by sludge. The use of forest land and municipal greening has become an effective way of sludge land use because it is not easy to pollute the food chain. Sludge is used for the restoration and reconstruction of seriously disturbed land (such as mine land, forest logging field, landfill, seriously damaged surface area and other land requiring reclamation), which reduces the potential threat of sludge to human life, and not only disposes of sludge, but also restores the ecological environment.
Direct incineration of wet sludge after drying is widely used. Direct incineration of sludge without drying is not only very difficult, but also very uneconomic in energy consumption.
The sludge treatment method with incineration as the core is one of the thorough sludge treatment methods. It can carbonize all organic matter, kill pathogens and greatly reduce the volume of sludge; However, its disadvantages are large investment in treatment facilities, high treatment costs, high equipment maintenance costs, and the production of strong carcinogen dioxin.
Mechanical dewatering of sludge (also including sludge thickening) is mainly used to reduce the volume of sludge treatment (sludge thickening and mechanical dewatering can usually reduce the volume of sludge by about 4 times). However, in addition to the water content and related physical properties, such as fluidity, which are different from the original sludge, the chemical and biological properties of dewatered sludge cake do not change due to dewatering.
For sludge drying, due to the requirements of improving water evaporation intensity, artificial heat source is used, and its operating temperature (for sludge particles) is usually greater than 100 ℃. The treatment effect of drying on sludge is not only deep dehydration, but also heat treatment; In addition, the moisture content of the product of sludge drying treatment can be controlled below 20%, that is, it can inhibit the microbial activity in sludge. Therefore, sludge drying treatment can change the physical, chemical and biological characteristics of sludge at the same time.
With the strengthening of environmental protection and people's further understanding of the limitations of existing sludge treatment and disposal technologies, countries all over the world are investing heavily in the research and development of new technologies to find a more economical and reasonable sludge treatment scheme.
For the biological treatment system of precipitated sludge, the engineering design innovation adopts the design of buried, compact and multi-stage digestion reactor. Several independent anaerobic digestion reactors are integrated with each other, saving building materials and adopting concrete structure, with low cost. The existing anaerobic digestion reactors at home and abroad generally adopt the above ground structure, which can make the equipment easy to maintain and facilitate the discharge of biogas residue to prevent biogas residue sedimentation. The engineering design of the biological treatment system well solves the maintenance of supporting equipment and biogas residue sedimentation. The system is equipped with less equipment. Only a few water pumps are needed, that is, if the water pump is broken, it will take less than 20 minutes to replace one, so as to ensure that the equipment maintenance will not stop production; The precipitated sludge is washed to remove the inorganic sewage soil that is easy to precipitate, and the organic sludge will float without sedimentation under the action of the blowing and floating system. The buried anaerobic digestion reactor not only has less investment and does not occupy land, but also can prevent earthquake, lightning and long service life, and reduce the heat loss of the digestion system.
There are three traditional sludge treatment methods: incineration, landfill and resource utilization. Incineration technology is mostly used abroad, but the investment is huge, which is easy to cause air pollution; Landfill is mostly used in China, but it needs to occupy a lot of land, which will cause secondary pollution to the environment at the same time; There are few land renewable resources in large and medium-sized cities such as Shanghai in China, so it is difficult to adopt this method for a long time. Chen Liqiao said that there are broad prospects for treating sludge with microorganisms. Through the field test and practical application of sewage treatment plant, the economic benefit of about 150 yuan can be obtained for each ton of sludge treated. Shanghai discharges about 1.4 million tons of sludge every year. If 20% of the sludge is treated by microbial aerobic fermentation, the direct economic benefit is about 42 million yuan. In addition, the use of microbial aerobic fermentation can also eliminate the odor of sludge, effectively control the secondary pollution of sludge, and the environmental benefits are also significant.
6. Done. It should be overturned when the temperature reaches above 65 ℃ in the second to third days. Generally, the fermentation can be completed within one week. The material is dark brown, and the temperature begins to drop to normal temperature, indicating that the fermentation is completed. If there are too many sawdust, sawdust and rice husk auxiliary materials, the fermentation time shall be extended until it is fully decomposed.
Fermented organic fertilizer has good fertilizer effect, safe and convenient use, disease resistance and growth promotion, and can also improve soil fertility.
Lime dosing technology
The dewatered sludge enters the hopper. Lime and aminoxanthic acid are added into the hopper. The lime dosage is 10% - 15% of the wet sludge dosage, and the aminoxanthic acid dosage is about 1% of the lime dosage. Because aminoxanthic acid produces ammonia in the reaction process, the sterilization effect of the whole process is enhanced and the reaction temperature is reduced. After the sludge, quicklime and aminoxanthic acid are stirred in the hopper, they are pushed into the feed port of the plunger pump by the double screw feeder, and sent to the reactor through the plunger pump. They stay at 70 ℃ for 30 minutes. The output products can meet the American EPA part503 class a standard. The sludge after reaction is pumped to the silo, and the gas generated in the sealed container is discharged after being treated by the washing tower.
PH > 12, long duration, complete sterilization; High pH precipitates most metal ions and reduces their solubility and activity; The solid content of sludge can be increased to 30%; The odor in the sludge is removed, and the system is fully sealed without environmental pollution; The system is fully automatic and easy to operate and maintain: a small amount of aminoxanthic acid is added to reduce the amount of lime and reaction time, and reduce the operation cost.
The so-called sludge carbonization refers to the process of releasing the water in the sludge through certain means, while retaining the carbon value in the sludge to a great extent, so as to greatly improve the carbon content in the end product (sludge carbonization o in the world, sludge carbonization is mainly divided into three types.
1. High temperature carbonization. During carbonization, there is no pressure, and the temperature is 649-982 ℃. First dry the sludge to a moisture content of about 30%, and then enter the carbonization furnace for high-temperature carbonization and granulation. Carbonized particles can be used as low-grade fuel with a calorific value of about 8360-12540 kJ / kg (Japan or the United States). This technology can realize the reduction and recycling of sludge. However, due to its complex technology, high operation cost and low calorific value content in products, it has not been applied on a large scale, with 30 wet sludge on a large scale.
2. Medium temperature carbonization. During carbonization, no pressure is applied, and the temperature is 426 ~ 537 ℃. First dry the sludge to about 90% moisture content, and then enter the carbonization furnace for decomposition. Oil, reaction water (steam condensate), biogas (uncondensed air) and solid carbides are produced in the process. In addition to carbonization, there is no obvious economic benefit for other users in Australia.
3. Low temperature carbonization. There is no need to dry before carbonization. During carbonization, it is pressurized to 6 ~ 8 MPa and the carbonization temperature is 315 ℃. The carbonized sludge becomes liquid. The moisture content after dehydration is less than 50%. After drying and granulation, it can be used as low-grade fuel with a calorific value of about 15048 ~ 20482 kJ / kg (United States). This technology makes all the biomass in the sludge split by heating and pressurization, and 75% of the water in the sludge can be removed only by mechanical method, which greatly saves the energy consumption in operation. The complete cracking of sludge ensures the complete stability of sludge. During the process of sludge carbonization, most of the calorific value in sludge is retained, which creates conditions for the reuse of energy after pyrolysis 14T.
4. Sludge hydrolysis heat drying technology. By heating the sludge and hydrolyzing the viscous organic matter in the sludge at a certain temperature and pressure, the sludge hydrothermal drying technology can destroy the colloidal structure of the sludge and improve the dehydration performance and anaerobic digestion performance at the same time. With the increase of hydrothermal reaction temperature and pressure, the particle collision increases. The collision between particles leads to the destruction of colloidal structure and the separation of bound water and solid particles. After hydrothermal treatment, the moisture content of sludge mechanically dehydrated without adding flocculant is greatly reduced. Macroscopically, the hydrolysis of sludge shows that the concentration of volatile suspended solids decreases and the concentrations of COD, BOD and ammonia nitrogen increase. The hydrothermal drying technology adopts a slurry reactor, which preheats the slurry by flashing and waste steam back mixing, and the steam and machinery are mixed together to improve the treatment efficiency of the system; In the hydrothermal reactor, the way of direct mixed heating with steam reverse flow is adopted to strengthen the mass and heat transfer process, which can avoid local overheating, coking and carbonization. In the continuous flash reactor, the effective recovery of system energy is realized.
First, the raw sludge is pumped from the secondary sedimentation tank to another tank through the sludge pump, so as to be separated from the supernatant. Because the moisture content of raw sludge can usually reach 99.5%, the sludge must be concentrated. There are many feasible methods to reduce the volume of sludge. Mechanical treatment methods such as vacuum filtration and centrifugation are usually used before sludge is disposed of in semi-solid form. Generally, these methods are the preparation of sludge incineration treatment. If biological treatment is planned, most of them are concentrated by gravity sedimentation or air flotation. The sludge corresponding to these two cases is still in flow state.
The design and operation of gravity concentration tank is similar to that of secondary sedimentation tank in sewage treatment. The concentration function is the main design parameter. In order to meet the greater concentration capacity, the concentration tank is basically deeper than the secondary sedimentation tank. A gravity thickener with correct design and good operation can at least double the sludge content. In other words, the moisture content of sludge can be reduced from 99.5% to 98%, or less. It is worth mentioning here that the design of gravity thickener should be based on the analysis of Chinese results as much as possible, because the appropriate sludge load rate is closely related to the properties of sludge.
If dissolved air flotation is used for concentration, a small part of water is required, usually the effluent from the secondary sedimentation tank, and inflated under the pressure of 400kPa. This supersaturated liquid flows into the bottom of the tank, and the sludge passes through under atmospheric pressure. The gas adheres to or is surrounded by the solid particles in the sludge in the form of small bubbles, so as to drive the solid particles to float to the surface. The upper part of the concentrated sludge is removed, and the liquid flows back from the bottom to the dissolved air tank for inflation.
After the volume is reduced, the sludge contains a large number of harmful components, which need to be transformed into inert components before disposal. The commonly used method is biodegradation stability. Because the purpose of this process is to convert substances into final sterile products, digestion is often used. Sludge digestion can not only further reduce the sludge volume, but also convert the solids into inert substances, and there are generally no bacteria. Sludge digestion can be achieved through anaerobic digestion or aerobic digestion.
After the sludge is digested, the organic matter in the sludge can be removed and the sludge volume can be further reduced. Next, the sludge needs to be disposed of. A variety of methods can be used to effectively dispose of sludge. These include incineration, sanitary landfill and use as fertilizer and soil conditioner. Raw sludge can be used for incineration, which can effectively reduce the moisture content. Adding fuel can be used to cause and maintain combustion, and municipal waste may also be used to achieve this goal. Raw sludge and digested sludge can also be disposed of by sanitary landfill. The land application of sludge has been practiced for several years, but now it is limited to the treatment of digested sludge. The nutrient composition of sludge is conducive to plant growth, and its particle characteristics can be used for land improvement. These applications are limited to feed crops and non-human consumption, and the possibility of using them to support edible plants is being studied. The main limiting factors of sludge land application are plant enrichment, metal toxicity and water eutrophic pollution. The application of sludge can be through spraying by sprinkler, channel diversion or direct injection into soil. Dewatered sludge can be laid on the land and cultivated by traditional agricultural machinery.
The above words refer to the treatment of general sludge. Because sludge can cause environmental pollution, we need to make great efforts to make it harmless. Nowadays, many sludge with different characteristics that lead to different types of pollution are being studied. In this paper, I will describe a kind of sludge from human oil production and petroleum industry. This representative sludge is called oily sludge.
A large amount of sludge is produced, which contains a considerable amount of oil and must be removed before final disposal. The sludge produced by the refinery cannot be safely disposed of unless its oil content is removed to a certain extent. In addition, in the oil-water separation system and oil storage tank of the refinery, the treatment cost of sludge caused by the accumulation of oily raw materials is very high, and it causes serious pollution to the environment. Petroleum is a hydrophobic mixture, such as alkanes, aromatics, resins and asphalt. Many compounds are toxic, mutagenic and carcinogenic. Their emissions are strictly controlled because of their negative impact on human health and the environment. They are classified by the U.S. Environmental Protection Department and given priority to environmental pollutants.
As a physical treatment method, low temperature cold treatment technology can effectively increase the dewatering properties of sludge, change the structure of flocculant and reduce the water content around sludge. Compared with the "initial sedimentation", cold treatment can remove impurities in the solution, so it can achieve better concentration. This is the benefit of cold treatment. As far as we know, the feasibility of cold treatment technology to separate oil from oil sludge is not discussed in the current data. However, if natural conditions permit, cold treatment technology provides an effective method for the treatment and disposal of oily sludge in many countries.
By comparing the sludge after conventional treatment and cold treatment, we can find that there is a layer of oil floating on the sample after cold treatment. After, we can find that the test tube is divided into three layers: * * * the upper layer is clear oil slick, the bottom layer is dark sediment, and the middle layer is clear water. After 24-hour sedimentation of the original sludge, the floating liquid and bottom sediment can be seen, but there is no visible oil phase. The phenomenon described above reveals that simple cold treatment can effectively separate the oil in the oil sludge.
1 treatment equipment
Belt sludge dehydrator
The system mainly uses clean energy such as solar energy and geothermal energy as the heat source of sludge drying, which can dry the mud with water content of more than 80 into dry materials with water content of less than 35, saving electricity, coal and environmental protection; The whole system is automatic remote control, which effectively reduces the cost of sludge treatment and disposal, and provides a low-carbon and environmental protection solution for sludge treatment and disposal.
The system consists of:
Sludge conveying system
Greenhouse heating system
Sludge tipping and distributing system