Activated sludge cultivation steps and precautions

Active sludge is a general term for microbial populations and the organic and inorganic substances to which they belong. It was discovered in 1912 by Clark and Gage in the United Kingdom. Activated sludge can be classified into aerobic activated sludge. And anaerobic granular activated sludge, activated sludge is mainly used to treat sewage wastewater. The activated sludge process is a kind of aerobic treatment method for treating organic sewage by using suspended microbial flocs.

Complex microbes in activated sludge and organic nutrients in wastewater form a complex food chain.
The first to carry out the purification task are the oxygen-producing bacteria and the saprophytic fungi. The bacteria, especially the globular bacteria, play the most important role. The activated sludge with excellent function is a fungal group composed of globular bacteria with filamentous bacteria as the skeleton. The sedimentation is good. With the normal operation of the activated sludge, the bacteria multiply and begin to grow protozoa, which is a predator of bacteria.

Common protozoans of activated sludge are flagellates, meat caterpillars, ciliates and pipeworms. When the activated sludge matures, the ciliate and the bell worm are dominant;

The metazoan is a secondary predator of bacteria. For example, rotifers, nematodes, etc. can only appear when the dissolved oxygen is sufficient, so when the metazoan occurs, the water quality improvement indicator is treated.

Performance indicators include: mixed liquid suspended solids (MLSS), sludge settling ratio (SV), sludge index [sludge volume index (SVI), sludge density index (SDI).

How to cultivate activated sludge in the water treatment section?

The sewage treatment plant is based on the preliminary acceptance of the unit test and the linkage test. The quality and quantity of sewage entering the water can meet the requirements of the initial operation, and the trial operation can be carried out. First, it is necessary to cultivate activated sludge, which is usually directly cultured through sewage.

After the urban sewage is introduced into the aeration tank, the water is suspended and aeration is performed. When the water temperature and temperature are suitable, flocs will appear in 1~2 days. At this time, a small amount of continuous water can be introduced, or intermittent water can be introduced continuously for continuous aeration. After one week of continuous aeration, the microscopic examination shows that the growth of the fungus can be gradually increased from small to large to the design amount, and put into trial operation.

If the nutrition is insufficient, some feces, nitrogen and phosphorus-rich waste liquid from the food processing industry, and rice bran water in the restaurant can be added to increase the speed of cultivation.

Also note that in the early stage of culture, because aerobic bacteria are not formed in large quantities, the amount of aeration should be controlled to avoid aging of aerobic bacteria.

How to cultivate anaerobic sludge in the sludge treatment section?

Large and medium-sized sewage treatment plants generally have good residual sludge after the water treatment section is normal, and it is more advantageous to cultivate anaerobic sludge.

First, the digester is filled with secondary effluent, and the anaerobic sludge strains of other digester are added, or the excess sludge of the water treatment section is connected.

In the place where the source of digested sludge is lacking, organic waste such as human feces, cow dung, pig dressing, distiller’s grains, and remaining starch may be diluted to a nitrification tank with a solid content of 1% to 3%.

When cultivating digestive sludge bacteria, it is necessary to control the pH value and the organic matter dosing load, and the pH should be maintained between 6.4 and 7.8. The organic load is controlled below 0.5 kg VSS / (m3 • d). Too high a loading load will result in a large accumulation of volatile fatty acids, a decrease in pH, and a too long acid decay phase, thereby prolonging the incubation time.

Stir the mixed sludge in the digester thoroughly. At medium temperature digestion, the water temperature in the digester should be kept at 35 °C ± 2 °C, and heated while entering the mud. After adding to the required temperature and mixing, the mud is suspended. After the anaerobic digestion and normal production of gas, the amount of mud can be increased one by one until the normal mud is added.

Analyze the biogas composition daily. When the required data is normal, take the sample for ignition test (pay attention to fire prevention and explosion protection) before the biogas utilization work can be formally carried out.

What should I pay attention to during the test run?

When the activated sludge is successfully cultured, the sewage treatment plant can be put into trial operation. The amount of water for the test run can be arranged according to the incoming water condition. Generally, when the test run is started, it runs according to half of the design amount, and when it is normal, it is put into the other half of the test run.

In order to determine the optimum process operating conditions during the test run, the main factors considered as variables are the temperature, pH, conductivity of the sewage, dissolved oxygen and sludge concentration in the aeration tank, mud temperature in the digester, pH値, and heated sludge system. The operation, the operation of the biogas cabinet, and the operation of the dehydrator.

The important parameters of the activated sludge process, BOD5, CODcr, MLSS, MLVSS, ammonia nitrogen, total phosphorus, etc., need to be monitored daily by the laboratory to adjust the process parameters. SV, SVI, microscopic examination, can be tested several times per day according to actual needs, and the process can be adjusted at any time.

Sewage treatment and sludge treatment should be controlled and adjusted in the trial operation stage. The control and observation, recording and analysis of the sludge should be carried out, and the sewage treatment volume, sludge treatment volume, sludge production, Biogas production, chemical consumption, production electricity consumption, and tap water consumption should be recorded in detail. Adequate analytical data should be provided for the quality of the influent and effluent, the aerobic sludge index, the anaerobic activated sludge index, the dewatered sludge index, and the biogas composition, so as to improve the quality of the sewage treatment.

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Municipal sewage treatment plant sludge treatment and disposal methods

The sewage from the municipal sewage treatment plant refers to the solid, semi-solid and liquid wastes produced after sewage treatment. It contains a large amount of organic matter, heavy metals, pathogenic bacteria and pathogenic bacteria, etc., without any treatment, it will cause serious damage to the environment. Pollution. The overall requirements for sludge treatment are stabilization, decontamination and reduction. There are many methods for sludge treatment and disposal at home and abroad, generally using concentration, digestion, dehydration, drying, effective use (mostly for agricultural use), landfill and incineration, or a combination of several methods. It should be said that the treatment and disposal of sludge from sewage plants is quite different from that of advanced countries.

The stabilization and dewatering of sewage sludge (generally dewatering to a moisture content of 70% to 80%) is usually referred to as sludge treatment; composting, landfilling, drying, heat treatment and final utilization of sludge are called Disposal of sludge. If the toxic and harmful substances in the dewatered sludge exceed the agricultural standards, sanitary landfill and sludge drying and incineration technologies should be considered. From the development of foreign sludge treatment, the control of sludge for farmland is becoming more and more strict in Europe, Japan or the United States, and the proportion of sludge drying and heat treatment is increasing year by year.

1. Treatment of sludge

The sludge stabilization treatment has aerobic stability and anaerobic stability. Aerobic stabilization has many advantages, but the energy consumption is very high, and it is only used when the amount of sludge is small. The anaerobic stabilization of sludge is usually carried out by a medium temperature (35 ° C) anaerobic digestion method. At present, more than a dozen large-scale sewage treatment plants have adopted this method. After the sludge is digested, the organic matter content is reduced, the performance is stable, the total volume is reduced, and a large amount of biogas is generated during the sludge digestion process (digestion degradation of 1 kg COD can produce 350 L of biogas) recycle and re-use.

However, due to the complicated process of the digesting device, the one-time investment is large and the operation is difficult. The cost of sludge anaerobic digestion and biogas utilization equipment accounts for about 30% of the investment and operation costs of sewage treatment plants, and most of them require imported technology and equipment. From the actual operation of the surveyed digester, only a few achieved the expected results. There are management and design issues, as well as the economic and safety issues of biogas utilization.

In addition to the anaerobic digestion of sludge, the sludge stabilization problem should be combined with the scheme of reducing sludge generation and stabilizing mud in the sewage treatment process. For example, in the design of sewage treatment process, the wastewater aeration time is extended to reduce the sludge production; the sludge mud age (such as the mud age of more than 20 days) is increased in the design parameters, and the sludge tends to be stable to the sewage treatment process. For small and medium-sized sewage treatment plants, it is advisable to use a treatment process with a delayed aeration function (such as a treatment process such as oxidation ditch). Some sewage treatment processes have low investment (such as section A of the AB method), and the amount of sludge is large, which increases the treatment cost of sludge.

The stability of the sludge does not mean that the sludge is harmless. The farmland also needs to meet the national standard for the control of pollutants in the agricultural use. Among them, the requirements for cadmium, mercury, arsenic, benzopyrene and polychlorinated biphenyl are relatively high, and the nature of sludge should be controlled by strictly controlling the discharge of industrial wastewater sources.

In terms of sludge stabilization, in addition to biological methods (including medium temperature digestion, high temperature digestion and utilization of microorganisms and certain additives), chemical methods are also used, and some dehydrated sludge is added with hydrochloric acid to adjust the pH to 2~ 3, the reaction for 60 minutes followed by the addition of sodium nitrate; some added lime to the dewatered sludge. The latter is used more in Europe.

2. Disposal of sludge

(1) Compound fertilizer

For most sewage plants (especially a large number of small sewage plants), sludge is a feasible and realistic solution for farmland. The nitrogen, phosphorus, potassium and trace elements in the sludge increase the yield of crops; the organic matter and humus in the sludge are good soil amendments. The sludge is properly concentrated, dehydrated and transported to the suburbs or neighboring provinces as agricultural fertilizers, which is the method adopted by many sewage plants. However, fertilization in farmland is seasonal. When mud is not needed, the sewage plant will be muddy and affect normal operation. Therefore, some sewage plants pay the fees, so that the farmers can pull the sludge away without asking where it is going, which will cause secondary pollution.

(2) Sanitary landfill

This method covers a large area and has a large amount of operation. In the rainy season, the sludge is more difficult to compact, and the site needs to be selected after the use period. The use of sludge sanitary landfill for large-scale sewage plants is a last resort. The cost of sanitary landfills is not low. There are also biogas safety collection systems for sanitary landfills in foreign countries. There are special requirements for layered and covered soil, drainage and greening. In view of the rising land prices and the smell of landfills, in recent years, regardless of the EU countries or the United States, Japan, the proportion of sludge sanitary landfill is getting smaller and smaller, and the existing landfills in the United States will be gradually closed.

Some cities intend to ship sewage sludge to urban landfills for disposal. There are two practical problems: First, management system problems. The layout, design and investment of the waste transfer station and landfill are managed by the Environmental Sanitation Bureau, while the sludge of the sewage treatment plant is managed by the municipal system. The design of the landfill site and the distance of the site are not considered to accept the sludge from the sewage plant; The dewatered sludge has a high moisture content. The sludge transported to the landfill requires a moisture content of not more than 30%. At present, the dewatered sludge moisture content of the sewage plant is 70% to 80%. Such sludge is not easily crushed and landfilled unless the sludge is properly prepared. Dry or add lime and flocculant treatment. Regardless of the landfill, the sludge should be treated with a high dryness dewatering scheme.

(3) Drying and incineration

Since the combination of sludge drying and sludge incineration has less one-time investment than single sludge incineration and low treatment cost, sludge drying is often a pre-treatment of incineration. The sludge drying can control the moisture content of the sludge to 10% to 40%, reduce the volume and weight of the sludge, reduce transportation costs and landfill fees, and greatly reduce the odor of the sludge.

The drying device is divided into direct drying and indirect drying, and its energy consumption is related to sludge composition and moisture. Indirect drying (using biogas through a heat exchanger) is generally recommended with a vertical drying unit and a fluidized bed process. In the tandem process of drying and incineration, the degree of drying depends on the calorific value of the sludge and the heat energy of the recovery incinerator, so that the energy of the drying is balanced as much as possible without additional fuel. The design and drying of sludge in Shanghai Shidongkou has high calorific value and energy balance. Sludge fluidized bed incinerator, the temperature is above 800 °C, the sand is recycled in the furnace, and the external exhaust gas should be properly treated.

If dewatered sludge is incinerated together with garbage, the foreign experience is to add 15% to 20% of sludge with a water content of 30% per ton of waste. The drying and incineration of sludge is likely to be the development direction of large sewage treatment plants in some big cities. Of course, due to the strict requirements for dust removal from incinerators abroad, in addition to the use of electric dust removal, it is necessary to cool down and heat, add acid and alkali to achieve smokeless dust emissions.

(4) Comparison of landfill and incineration

Comparing the schemes of sludge sanitary landfill and incineration disposal, the main process flow is:

Original sludge→concentration→digestion→dehydration→sanitary landfill

Original sludge → concentration → (digestion) → dehydration → incineration → incineration ash landfill

For the incineration treatment process, in order to avoid the reduction of the calorific value of the sludge after digestion, it is also possible not to carry out sludge digestion and disposal. The economic comparison results of the above two processes, regardless of the use of domestic equipment or imported equipment, the disposal costs of the two are basically the same. The sludge is disposed according to domestic equipment, and the operating cost is converted into sludge dry solids. The total cost of treatment is about 800 yuan/t. The 10,000 m3/d wastewater treatment plant produces 2 tons of DS, and the treatment cost per ton of sludge is about 0.16 yuan, which is compared with the domestic sewage treatment plant sewage treatment cost (excluding depreciation and repayment interest) 0.3-0.45 yuan/m3. The cost needs to be increased by 35% to 50%, which is equivalent to the foreign example.

Since the engineering cost and operating cost of sludge sanitary landfill and sludge incineration are roughly equal, the incineration scheme has obvious advantages from the harmlessness and reduction of sludge. This is also the reason why sludge incineration has developed rapidly in foreign countries (especially in Western Europe and Japan). The sludge in the Netherlands is 100% disposed of by incineration. After incineration, a small amount of sludge can be used for concrete, brick products, aggregates for roadbed pavement and backfill for engineering construction.

3.Sludge treatment and disposal should pay attention to the problem

(1)When designing urban sewage treatment facilities, industrial pollution source control, sewage treatment process and sludge treatment and disposal should be considered as a system. Based on the analysis of the sludge composition and quantity of the sewage treatment plant in the city, it is correct to comprehensively plan the sludge disposal, coordinate the multi-party relationship, and implement the phased implementation plan. The sludge treatment of the sewage plant is not seriously disposed, and the sewage treatment is incomplete.

(2) For the final disposal of sludge, our lack of experience, such as the drying of sludge and the design of incinerators, is much more complicated than the sewage treatment process. We should seriously study, introduce, digest and absorb foreign technology and experience. It is necessary to formulate and improve regulations and standards related to sludge disposal. The sludge digestion and biogas utilization devices of some sewage treatment plants in China are basically imported technology and equipment from abroad.

(3) Use multiple ways to solve the sludge problem. The big factory is different from the small one, and the south and the north are different. In some places, sludge can be combined with garbage disposal, and some local sludge can be combined with coal-fired power plants. For the sludge of a small sewage plant with a large amount of land, it is necessary to summarize the experience of agricultural use. In the sludge drying and heating technology, various solutions such as solar energy, microwave and wet oxidation can also be considered. Some sludge can be treated together with sludge in industrial wastewater treatment. It is necessary to be good at summing up the experiences and lessons of various places and vigorously developing localized equipment. This is a sunrise industry. It is necessary to actively explore low-cost, harmless and multi-purpose sludge treatment and disposal methods suitable for national conditions.

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Brief introduction of harmless treatment technology of oil sludge

With the increasing awareness of environmental protection and strict environmental standards, oil sludge, a dangerous solid waste containing petroleum resources, must be detoxified, reduced, and resourced. At present, for the treatment of oil sludge, domestic and foreign scholars and petrochemical-related enterprises have carried out a lot of research and formed a variety of oil sludge treatment technologies. Among them, the oil sludge treatment technology mainly includes: landfill disposal technology, curing treatment technology, biological treatment technology, profile control treatment technology, etc., in order to achieve the harmless, reduced and resource treatment of oil sludge.

First. Oil sludge landfill disposal technology

The oil sludge landfill disposal technology is a simple oil sludge treatment method. After the oil sludge is dehydrated and sealed, it is transported to the selected landfill for direct landfill. The treatment process is simple and rapid, the operation cost is low, and the operation management is simple, but the disadvantage is that the technology does not essentially treat the oil sludge, and the landfilled oil sludge not only occupies a large amount of land resources, but also fills in time. The buried oil sludge itself has a large amount of harmful components that are decomposed and will slowly infiltrate into the soil and surrounding groundwater, causing secondary pollution. Although the landfill has changed from an early natural attenuation type to a closed landfill, the above problems still exist. This technology is widely used in the early stage of oil sludge treatment at home and abroad. With environmental awareness and shortage of land resources, many countries have issued regulations prohibiting landfill disposal of oily sludge, but there are still some regions and countries. This method is still used to treat oil sludge.

Second, oil sludge solidification treatment technology

The process of curing the oil sludge is to transform the toxic and hazardous hazardous waste into a low-solubility, low-toxicity and low-migration substance, and to stabilize the toxic and harmful substances. The oil sludge solidification treatment technology is used in the early stage. To deal with radioactive sludge, the technology has developed rapidly in recent years. The oil sludge solidification treatment technology refers to the mixing and solidification of oil sludge with different kinds of solid agents, coagulants and additives, so that some properties of the oil sludge are irreversibly changed, thereby forming a solid body with better integrity.
The oil sludge solidification treatment technology is a mature treatment method capable of basically achieving harmlessness, simple treatment process and low operation cost, but the process uses a large amount of high-energy curing raw materials in the treatment process, after treatment The volume and weight of the cured product are greatly increased, and the curing agent has high requirements on the characteristics of the treated sludge. The current research mainly focuses on the development of the curing additive and the stabilization of the agent.

Third, the oil sludge biological treatment technology

The oil sludge biological treatment technology is to put special microbial strains into the oil sludge, so that the bacteria can grow and grow in the environment of oil sludge, and use this biological process to consume the organic matter in the oil sludge, and then to digestion into CO2 and H2O to achieve the purpose of removing all kinds of organic pollutants in oil sludge. The mechanism of the treatment mainly has two aspects: (1) A microbial flora with high-efficiency degradation ability naturally formed and screened and separated is added to the oil sludge; (2) By adding nutrients such as nitrogen and phosphorus to the oil sludge or mediating nutrient factors, the high-efficiency degradation activity of the microbial flora is stimulated by measures such as aeration, temperature control, and pH adjustment.

The main point of biological treatment of oil sludge is the selection and cultivation of the flora. Although this technology has many advantages, such as simple operation, energy saving, almost no need to add chemical reagents, and little environmental pollution, it also has its own limitations. , such as long processing cycle, unable to recover oil resources. The screening and cultivation processes of microbial flora are complicated, and the microbial community itself has limited tolerance to hydrocarbon organic matter, and is not suitable for treating high oil content sludge. Therefore, it is the future focus to screen the microbial flora with high ability to degrade.

Forth. Oil-sludge profile control technology
The oil sludge in the oilfield is produced from the stratum, and its composition includes water, crude oil, waxy, muddy sand, colloidal asphaltene, etc. This type of oil sludge has good compatibility with the formation, and the oil-sludge sludge profile control technology is based on “ From the viewpoint of the stratum and the stratum, the oil sludge is injected back to the bottom layer. This special refilling liquid needs to adopt some corresponding treatment methods, such as adding appropriate amount of emulsifier, suspending agent, etc. to enhance the solid particles of oil sludge. The effective suspension and extended suspension time are formulated into a uniform and stable profile control agent. The oil-containing sludge profile control agent is injected back into the formation. After entering the formation to a certain depth, the adsorption of the embedding dispersant by the formation rock and the release of the formation water cause the stable profile control agent system to start to decompose, and the mud sand particles in the profile control agent are adsorbed. After waxy and colloidal asphaltenes, particles with relatively large particle size are formed by adhesion and aggregation, and the pore size is reduced in the large pores, which makes the seepage resistance of the subsequent water injection greatly increase, effectively blocking the core of the formation, and thus greatly effect of water injection development has been improved and the oil recovery rate has been improved.

At home and abroad, it is very active in the research and application of oil-containing sludge profile control technology, and there are many oil fields that have been put into use. However, due to the large difference in the composition and characteristics of the sludge from different sources, different profile control agents need to be prepared for different sludges, and there are certain requirements for the treated sludge, for example, the oil content cannot be too high. Therefore, the application range of the technology is limited.

 

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Characteristics and hazards of oil sludge

The oil sludge is mainly composed of three phases of water, oil and slag. The characteristics of oil sludges of different types and different sources vary greatly. The content of the three-phase components in the oil sludge will directly determine the available value of the oil sludge, and also processing this type of oil sludge process provides initial parameters. The specific resistance of oil sludge is very large, almost 40 times that of ordinary oil sludge, and its compressibility coefficient is 20 times larger than that of general oil sludge. Therefore, oil sludge belongs to difficult-to-filter oil sludge.

The water content of oil sludge is generally relatively large. For example, the water content of oil sludge in refinery is generally above 60%, and the moisture content of ground oil sludge is as high as 30%. The water and oil in oil sludge form oil-in-water. The difficult state of water-in-oil separation. In addition, a large number of different types of chemical treatment agents, as well as a large number of water treatment agents such as coagulants, fungicides, scale inhibitors, and scale inhibitors, are added to the crude oil extraction and subsequent treatment processes. The contamination components in the oil sludge are made more complicated, and the added additives interact to form a stable and fully emulsified structure, making it difficult to separate the three phases. The oil sludge usually contains a relatively high concentration of heavy metals. The oil sewage from the refinery is added with polymeric iron and polyaluminum in the treatment, resulting in high iron and aluminum content in the oil sludge.

Oil sludge has been listed in the HW08 waste mineral oil in the “Dangerous Waste List”. The oil sludge is complex in composition. In addition to containing a large amount of petroleum, it also contains various types of bismuth, phenols, benzenes, and strontium. Toxic and substances, a large number of pathogenic bacteria, parasites (eggs), heavy metals such as Cu, Zn, Cr, Hg, Pb, salts and polychlorinated biphenyls, dioxins, radioactive nuclear elements and other toxic and harmful substances that are difficult to degrade. The hazard to the soil is generally that the oil sludge will occupy a large amount of agricultural arable land if it is not treated and piled up, which will increase the shortage of land resources; it will also change the original nature of the soil, affect the growth of soil vegetation, and cause soil microorganisms. The species cannot survive and the soil ecosystem is destroyed. During the long-term open-air stacking of oil sludge, the toxic and harmful substances such as organic matter, heavy metals and pathogens are leached by the water stream and the rainwater is leached, and the surface water is remitted with the water. Infiltration into groundwater will cause the groundwater COD, BOD and other indicators to exceed the standard seriously; the volatile substances contained in the oil sludge will slowly diffuse into the surrounding atmosphere, producing a foul smell and unpleasant smell, and the benzene series contained in the volatile matter. Substances are carcinogens, and long-term exposure is extremely harmful to human skin and mucous membranes.

The oil sludge pyrolysis gasification device can separate the oil sludge with high oil content and extract the oil in the sludge. This process not only solves the environmental pollution, but also realizes considerable economic value and has broad application prospects.

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Composition of Municipal Solid Waste and Its Regional Impact

Composition of municipal solid waste (MSW) is one of the key parameters directly affecting the selection of waste treatment methods and the design and planning of treatment facilities. It is a dependent variable affected by many factors, such as geographical environment, energy structure, economic development, living habits, living standards, climatic characteristics and waste recycling. According to China’s relevant standards, the composition of municipal solid waste is divided into four categories: organic matter, inorganic matter, recyclable matter and other garbage. Organic matter can be divided into plant waste and animal waste. For household waste, it mainly consists of kitchen waste such as vegetables, meat and aquatic products. Inorganic wastes, such as lime, brick, tile and ceramics, are of low recycling value and will not cause serious harm to the natural environment. The classification of recyclables mainly considers the technological requirements in the process of material utilization and resource regeneration after recycling. It can be divided into paper, plastics, rubber, textile, wood and bamboo, glass, metal and other types in order to facilitate the comprehensive utilization of waste products.

The results of dynamic statistics show that while the output of municipal solid waste in China is increasing rapidly, the composition of municipal solid waste has also changed greatly. Despite the unbalanced economic development in different regions, the composition and characteristics of municipal solid waste are very uneven. However, the composition of municipal solid waste shows a consistent trend in both southern and Northern cities, large and small cities. That is to say, the inorganic composition decreases significantly with the passage of time, while the perishable and recyclable materials do. Generally increasing, the proportion of combustibles is also increasing, which will have a greater impact on the development of municipal waste treatment and disposal technology in the future. Its characteristics can be summarized as follows:

(1) There are obvious differences in the composition of garbage between big cities and small and medium-sized cities. Organic matter accounted for 31%-36% of the total amount of municipal solid waste, inorganic matter accounted for 60%, waste accounted for 4%-6%, organic matter accounted for 20% of the total amount of municipal solid waste in small and medium-sized cities, inorganic matter accounted for 75%, and the proportion of waste was lower.

(2) In terms of geographic environmental impact, the proportion of organic matter and combustible matter in urban garbage in southern China is higher than that in northern China. The main reasons are as follows: the proportion of coal burning and the utilization rate of living energy in northern cities are higher or longer than those in southern cities due to climate differences, so the proportion of ash and residue in garbage increases and the proportion of organic matter decreases relatively; the difference of dietary structure leads to the consumption of fruits and vegetables and the consumption period of fruits and vegetables in southern cities are larger or longer than those in northern cities. In terms of the overall economic level, the southern municipal solid waste is higher than the northern municipal solid waste, so the proportion of paper, plastics, rubber and other combustibles and recyclables in the garbage is relatively large. Relevant analysis shows that the composition of municipal solid waste in small and medium-sized cities is closely related to the geographical environment. Organic matter in municipal solid waste in the North accounts for about 16.42%, and organic matter in municipal solid waste in the south is obviously higher than that in the north, 28.54%. However, for large cities, although their geographical environment and other basic conditions are different, because the consumption level of urban residents is relatively high, the organic content gap in urban garbage is relatively small. Therefore, with the development of economy, the development of the artificial environment of city will be more perfect, the influence of natural environment on the life of urban residents will be less and less, and the influence of natural environment on the composition of municipal solid waste will also be weakened.

(3) The proportion of organic and combustible substances in garbage in economically developed areas or cities is relatively large, whether in the South or in the north. For example, the contents of kitchen waste, paper, plastic and rubber in the economically developed large cities are higher. Take kitchen waste as an example: 70% in Shanghai, 63% in Guangzhou, 58% in Shenzhen, 52% in Nanjing and 50% in Tianjin. However, in small and medium-sized cities with low consumption level and energy gasification rate, the organic component of domestic waste only accounts for 22.48% of the total amount of garbage, and the inorganic component accounts for 65% of the total amount of garbage. The proportion of recyclable materials is very small.

(4) Fuel structure has a significant impact on the yield and composition of garbage. With the popularization of urban central heating and coal gasification, great changes have taken place in the structure of civil fuels, as well as in the composition of municipal solid waste. The main manifestation is the influence of inorganic substances in garbage, i. e. the amount of coal ash. For coal-fired areas, the proportion of coal ash and slag in refuse can reach as high as 70%~80%; for gas, the proportion of coal ash tends to zero theoretically, but because of the existence of ash and slag soil, its inorganic composition is about 30%. Relevant data show that the fuel structure affects the daily production of organic matter per capita to a certain extent, which also affects the composition of garbage.

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Routes, classification and management measures for solid waste generation

The treatment of solid waste can effectively dispose of waste, reduce the discharge of final waste, reduce the environmental pollution to the area, prevent the spread of secondary pollution, and at the same time achieve low total treatment cost and high resource utilization efficiency. And how is the path and classification of solid waste generated?

The path of social material flow and solid waste generation, which maintains all activities in human society, is in a state of dynamic equilibrium and follows the law of conservation of mass. Get two inspirations:

1. All human activities, relative to the external environment, are simply the development and utilization of natural resources, and eventually return the resources to the environment in the form of waste. This “utilization and return” of resources is often in an alternating state. In the production and consumption of products, all forms of waste are produced. Some of these wastes are recycled and reused in production and consumption, and are returned in the form of waste just in the same amount as the raw materials developed in the environment. In the natural environment, a closed circulation system is formed.

2. In modern society, every aspect of human activities produces wastes of various states, from the development of raw materials in the environment to the utilization of products, without exception. The way to reduce waste production is to reduce the consumption of raw materials per unit of product and reduce the development of raw materials. Solid waste is an integral part of the social logistics system and follows the above rules.

The classification of solid waste is based on the route and nature of its production.

In developed countries, solid waste is divided into four categories: industrial waste, mining waste, agricultural waste and municipal waste. In the “Fixed Waste Management Law” enacted in China, solid waste is divided into two types: solid waste (dust) and municipal waste.

Industrial solid wastes containing hazardous ingredients are classified as a “hazardous waste” sub-category because of their particular hazard to the environment and humans.

Solid waste treatment management measures

Solid waste treatment is done by physical means (such as crushing, compression, drying, evaporation, incineration, etc.) or biochemical actions (such as oxidation, digestion and decomposition, absorption, etc.) and pyrolysis gasification to reduce its volume and accelerate its The process of natural purification. Let’s take a look at the main measures for solid waste pollution and the use of solid waste resources.

The main measures for solid waste pollution and utilization of solid waste resources are:

1. Reform the production process and reduce waste: improve product quality and produce products with long service life so that the articles do not become waste quickly. Use concentrate to reduce waste emissions during production. For example, in the beneficiation process, the iron ore grade can be increased, and the slag-forming agent and coke can be added less, thereby reducing the discharge of the blast furnace slag. After adopting this method in industrial advanced countries, the blast furnace slag emissions can be reduced by more than half.

2. Development of material recycling technology: reforming traditional processes, developing material recycling processes, making the waste of the first product a raw material for the second product, and making the second product waste a third product. Raw materials, etc., leaving only a small amount of waste into the environment, so that economic, environmental and social benefits can be achieved.

3. Incorporate solid waste into the scope of resource management: formulate a solid waste resource policy and encourage the use of solid waste. A solid waste resource system was established to include wastes with clear uses into resource allocation plans; wastes that were temporarily unavailable could be stored as backup resources.

4. Formulate regulations for the management of solid waste: The policies concerning the pollution of solid waste and the use of solid waste are reflected through legislative means. Some countries have solid waste management regulations and environmental standards.

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Brief Introduction of Technology for Disposal of Dangerous Waste in Cement Rotary Kiln

principle

Cement rotary kiln is the main equipment of cement clinker dry and wet production line. Rotary kiln is widely used in gold treatment, chemical industry, building refractories, environmental protection and other industries. A large number of research and practice show that the cement rotary kiln has high combustion temperature, long residence time in the kiln, negative pressure operation and stable working conditions. A large number of harmful substances are reduced in the kiln, and the exhaust gas discharge meets the requirements of non-environmental protection, and the waste residue is not discharged outward. At the same time, this kind of disposal process is carried out synchronously by using cement production process, and the disposal cost is low. Therefore, it is considered as a reasonable disposal method by foreign experts.

structure

Cement rotary kiln is composed of cylinder, transmission device, supporting device of supporting wheel and baffle wheel, lining of kiln, sealing of kiln tail, kiln head and fuel device, etc.

classification

According to the different heating methods, it can be divided into internal heating and external heating.

The material of internal heating rotary kiln is directly in contact with flame and flue gas. The atmosphere of oxidation or reduction in the furnace can be adjusted. Refractory bricks are laid on the inner wall of the cylinder. The inner lining of the head and tail cover is high-strength and wear-resistant castable. The flexible seal between the head and tail cover and the cylinder can completely prevent dust and leakage. It can adopt multi-stage support, so that the length of the cylinder can reach 60 meters, and the maximum service temperature can reach 1600 C. The output is large, and the suitable fuels are liquefied gas, natural gas, gas, fuel oil, pulverized coal, coal, etc.

The material of external heating rotary kiln does not contact with flame and flue gas directly. The heat source is between the furnace and the cylinder. The material is heated by heat transfer through the heat-resistant steel cylinder wall. The inner lining of the furnace is made of refractory fibers, which can save energy and reduce consumption. Limited by heating mode and material of the cylinder, the length of the cylinder is generally less than 15 meters, and the heating temperature is less than 1200 C. The output is small, suitable heating methods are: electric heating, gas, fuel oil, coal and so on.

Other

1. Treatment of Hazardous Waste in Cement Rotary Kiln

According to the Law of the People’s Republic of China on the Prevention and Control of Environmental Pollution by Solid Wastes: Wastes with one or more hazardous characteristics, such as corrosiveness, toxicity, flammability, reactivity or infectivity, and wastes with hazardous characteristics, which may have harmful effects on the environment or human health, are among the hazardous wastes. For example: medical wastes, pesticide wastes, heat treatment cyanide wastes, waste emulsifiers, fuel and paint wastes, explosive wastes, and wastes containing hazardous chemical components, such as zinc-containing batteries as we often mentioned, and a large number of hazardous wastes produced in industrial production and scientific experiments. Knowing these, do you think that dangerous waste originally was around us? We are alarmed by its wide source and huge quantity. The damage of dangerous waste to human body and ecological environment has been paid attention to by all countries in the world. Some people call dangerous waste “political waste”. From this, we can see that dangerous waste has brought troubles to people’s lives. Good disposal and reuse of hazardous wastes has become the top priority in building a green, low-carbon, environmentally friendly and energy-saving life.

After a long time of continuous exploration and experiments, many methods of hazardous waste treatment have been summarized, such as burial, incineration, neutralization, extraction, magnetic separation, hydrolysis, precipitation and so on by chemical or physical methods. Among them, cement rotary kiln technology has become the most effective method for hazardous waste treatment and reuse because of its unique advantages. It has been widely used. Cement rotary kiln has high incineration temperature, stable state, more thorough waste combustion, cement rotary kiln is in a negative pressure state in operation, which avoids harmful gas spillover when dealing with hazardous waste, and because the rotary kiln has good tightness, it will not cause dust pollution and is conducive to environmental protection. Hazardous waste contains chlorine, sulphur, fluorine and other chemical components, which are completely absorbed in high temperature treatment and converted into non-toxic calcium chloride, calcium sulfate, calcium fluoride and so on. It is directly mixed in cement clinker, which has been proved that the quality of cement will not be adversely affected. When the waste is burned, it produces a certain amount of heat and saves coal-fired raw materials and production costs.

The advantages of cement rotary kiln in dealing with hazardous waste are: environmental protection, energy saving, safety, and certain economic benefits.

2. Smelting

In addition to burning cement clinker, cement rotary kiln is also used for burning clay, limestone and slag drying. In refractory production, rotary kiln is used for burning raw materials to stabilize its size, increase its strength and reprocess. In nonferrous and ferrous metallurgy, iron, aluminium, copper, zinc, tin, nickel, tungsten and chromium are sintered and roasted in rotary kiln. For example, aluminium hydroxide is roasted to alumina in aluminium production; pellets are produced for blast furnace ironmaking with aluminium hydroxide in ironmaking; iron ore is directly reduced by SL/RN method and Krupp method abroad; tin and lead are extracted by chlorination volatilization roasting method. In the process of mineral processing, the lean iron ore is magnetized by rotary kiln, so that the original weak magnetism of the ore is changed to strong magnetism, which is beneficial to magnetic separation. In chemical industry, baking soda, phosphate fertilizer and barium sulfide are produced in rotary kiln. This method has the advantages of low energy consumption, less electricity consumption, no use of sulphuric acid and the availability of medium and low grade phosphate rock, and is quickly popularized. In addition, in environmental protection, the use of cement kiln incineration of hazardous waste, garbage, not only to reduce waste, harmless, but also to use waste as fuel, save pulverized coal, achieve waste recycling.

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10 Tips for Energy Saving and Consumption Reduction in Concentrators

Energy saving and consumption reduction has become a very important task in the sustainable development of concentrators. We should take various effective measures to improve production efficiency, reduce energy consumption, and then improve the economic and ecological benefits of concentrators. The common methods of energy saving and consumption reduction in concentrators are as follows:

1. More grinding and less grinding to determine reasonable grinding size

Production practice shows that about 60% of energy consumption in mineral processing is consumed in the grinding operation of ore, so energy saving in mineral processing should first work hard in the grinding stage. For the concentrator being produced, the crushing and grinding equipment has been basically fixed, and efforts can only be made on how to balance the crushing and grinding capacity. This requires that, on the basis of guaranteeing the crushing capacity, the discharging outlets of crushers in each section should be adjusted reasonably, and the comprehensive capacity of crushing system should be brought into full play so as to reduce the final particle size of crushing system, reduce the pressure of grinding section and increase grinding efficiency.

2. Automatic control of crushing production

The automatic control system can realize the functions of sequence control, logical chain control, fault protection control, automatic control of crusher feeding and automatic control of ore bin distribution of crushing process equipment, reduce the labor intensity of workers, reduce the rate of equipment failure and improve the production efficiency of equipment.

3. Selection of High Pressure Roller Mill

High-pressure roll mill is composed of a pair of rollers which rotate synchronously in opposite direction. One of them is fixed roll and the other is movable roll. Compared with other crushing equipment, it has obvious energy-saving advantages. Material enters from the inlet port above the press roll and is brought into the roll room by the rotation of the press roll. After strong extrusion, crisp muffin is formed and discharged from the machine. In the crushing process of high-pressure roller mill, quasi-static crushing is implemented, which saves about 30% energy consumption compared with impact crushing. High-pressure roller mill implements material layer crushing, which is the mutual crushing between material and material. Comparing with other crushing methods, the crushing energy loss of compressive stress material layer is small, and the utilization ratio is high. The discharged cake not only contains a large proportion of fine particles, but also produces a large number of cracks in the particle, which improves the grindability of material for subsequent grinding, increases the production capacity of grinding system, and greatly reduces the grinding power consumption and steel consumption.

4. Selection of efficient large grinding equipment

Large grinders generally use advanced equipment such as hydraulic power, hydrostatic bearings and fuel injection devices, which effectively improve the economic benefits of the operation of the mill. At the same time, its unit energy consumption is significantly lower than before. The use of large ball mills can not only reduce energy consumption, but also enhance the stability of the process and improve production efficiency.

5. Improving classification efficiency

Classification efficiency has a very significant impact on the production capacity of concentrators. In order to ensure the scientificity and rationality of classification size, many concentrators currently use closed circuit grinding classification system in production. Overgrinding is particularly common in concentrating production, and it is also an important source of energy consumption.

Overgrinding is closely related to classification efficiency. At the present stage, a large number of new equipment are gradually appearing in the production link, which also ensures the effect of strengthening classification. Furthermore, the coarse-grained classification can also be accomplished by means of fine screening, so as to reduce the energy consumption produced in the operation of the screw classifier. High efficiency separation equipment such as hydrocyclone or high frequency fine screen can be used in fine particle classification. Under the function of intensified classification operation, the system can separate qualified particles in time, avoid over-grinding and effectively reduce energy consumption in grinding process.

6. Automatic control of grinding and classification

Actively take effective measures to implement automatic control. The automatic control system of ball mill can detect the audio frequency, power and grading current of the mill by itself, and make a comprehensive analysis and study of the running state of the mill. The automatic control can be realized in the aspects of ore feeding, concentration and grading overflow granularity. The efficiency of grinding and grading can be improved continuously, and the function of grinding and grading machine can be displayed to the greatest extent.

The investigation shows that after the automatic control of grinding and classification circuit, the output of grinding machine and the recovery of beneficiation metals increase obviously, the energy consumption decreases by 10%. The grinding process has strong stability and obvious advantages.

7. Selection of efficient sorting equipment

The use of new and efficient sorting equipment is one of the keys to realize energy saving and consumption reduction in sorting. At present, various types of flotation equipment emerge in an endless stream, and the quality is different. When selecting flotation equipment, schemes should be compared according to different conditions. For example, compared with the small flotation machine, the large flotation machine has the characteristics of low energy consumption, small floor area and high automation. Compared with the flotation machine, the flotation column can simplify the cleaning times, reduce the dosage of reagents and reduce energy consumption when obtaining the same grade.

8. Using Frequency Conversion Control Technology

As an effective way to save energy, frequency conversion control has been widely used in many mines. Frequency converter can realize soft start of motor, achieve energy saving and speed regulation by changing the input voltage frequency of equipment, and provide protection functions such as over-current, over-voltage and over-load for equipment. Frequency conversion control can be used on belt conveyor, compressor, slurry pump and other loads, which can not only rationally adjust process parameters, but also significantly reduce energy consumption.

9. Electricity for peak avoidance and valley filling

Because the peak price is much higher than the valley price, the implementation of peak power transfer, peak avoidance and valley filling, although the total electricity consumption has not been reduced, but can greatly save electricity costs and reduce production costs. Most concentrators produce continuously, but some links can be controlled. The crushing process makes full use of the powder silo in the intermediate buffer link of mineral processing production, carries out reasonable regulation and control, avoids peak and fills valley, carries out equipment maintenance during the peak period of power consumption, enlarges horsepower production during the peacetime and valley period, and only opens the main production equipment during the peak period of grinding and separation process, so as to minimize the cost of electricity consumption.

10. Continuous optimization of mineral processing process

Technology, equipment and technological process have a very significant impact on the quality and efficiency of production. Advanced energy-saving technology and energy-saving equipment improve the quality of mineral processing and simplify the process of mineral processing. If energy-saving technology and equipment can be applied scientifically in the process of mineral processing, it can play a positive role in a variety of processes, technologies and equipment, on the one hand, simplify the process. Processes, on the other hand, also reduce energy consumption.

In short, energy saving and consumption reduction is a long-term and arduous task for mineral processing enterprises. We should tap the potential of energy saving and continuously develop and apply new energy-saving technologies, new technologies and new equipment.

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Source and classification of oil sludge

Oil sludge is generally considered to be a mixture. The main components are: crude oil or refined oil, other organic components, mud, and water. It is a concomitant product produced during oil exploitation, oil wastewater treatment, petroleum refining, and petroleum production and processing. According to different sources of oil sludge, it can be divided into the following categories:

(1) Oilfield sludge

Oilfield sludge is mainly produced in the process of oil exploitation. This type of oil sludge mainly has two forms: oil sludge treatment and oil sludge from oil sludge treatment. The treatment of oil production and the treatment of oil recovery sewage will produce a mixture of oil sludge. The slag phase components in this oil sludge are generally derived from rock fines under the bottom layer, and the water content is generally high; Refers to the oil sludge formed by the mixing of instrument tools during the mining process or the occurrence of crude oil discharge and some accidental leakage and infiltration into the oil field soil. Such oil sludge generally has a small oil content and a large slag content. Different oil fields show different differences.

(2) Storage and transportation of oil sludge

As the name implies, the storage and transportation of oil sludge is generated during the later collection and storage of petroleum. The transportation of oil mainly depends on means such as oil pipelines, oil tankers and oil tankers, and then stored in the corresponding tank equipment. After long-term use accumulation, some heavy oil components in petroleum will be deposited on the bottom of the conveying device and storage device due to the high viscosity and high density. These heavy components and devices deposited at the bottom Some of the debris and particles form a storage sludge. The oil content of this type of sludge is generally high, and most of them are heavy component oils, and it contains a large amount of metal elements carried by materials of storage and transportation equipment, which is difficult to recycle.

(3) Oil sludge in refinery and chemical plant

In many processes of refinery plants, water resources are inevitably needed, and the sewage produced in the production process is complex in nature. The oil sludge produced in the process of treating sewage in refineries can be roughly divided into three categories: flotation cells. Scum, grease trap bottom mud and residual activated sludge. The addition of a large amount of chemical agents to the oily wastewater during the treatment process complicates the composition and nature of the oil sludge in the refinery. Generally, the floating oil sludge scum mud and the grease trap bottom mud are mixed and stored, and the activated sludge is stored separately. The main reason is that the first two types of oil sludge have high oil content and small slag content, and the latter sludge generally has low oil content. .

(4) Oil sludge produced during the process of synthesizing petrochemical products

This kind of oil sludge is produced in the petroleum petrochemical synthesis process, mainly from the oil residue or waste raw materials produced in the process of further processing crude oil or refined oil to produce synthetic products, such as oil sludge produced during the production of paint. Such oil sludges have a high oil content, most of which are heavy components, and a large amount of other organic substances are added during the production process, the components are complex, the viscosity is large, and it is difficult to handle.

The oil sludge pyrolysis gasification device can process oil sludge from different sources, and the pyrolysis gasification device can separate the oil sludge into three phases and extract the refined oil in the sludge. This technology not only solves the pollution of the environment, but also realizes considerable economic value and has broad application prospects.

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Pollution status of oil sludge in China

In recent years, although the pace of development of the petrochemical industry has gradually slowed down, demand and consumption are still increasing, and it is still the pillar industry of today’s world. While the petrochemical industry is developing, it has generated a large number of environmental pollution problems. In the process of exploitation, oil will produce oil sludge due to the operation process and treatment process. At the same time, a large amount of oil sludge will be produced in the petrochemical refining production process and the treatment of oil sewage.

The amount and storage of oil sludge is currently very large in China. In terms of domestic refineries and oil fields, the amount of oil sludge produced is increasing, especially in major oil fields in China. In addition, China’s major oilfield companies need to drill more than 2,000 wells, such as wells, production wells and production wells. In the process of drilling wells, each well will produce 70m3 ~ 100m3 of waste mud, making it only drill well every year. It produces about 4×104m3 of oil sludge. The following table shows the annual output of oil sludge in major oil fields in China.

                                                                Annual output of oil sludge
Oilfield      Liaohe      Shengli     Dagang      Henan      Daqing  Changqing
Output     2.4×105t     1.16×105t     1.5×105t     5×104 m3    1.4×105m3   2.78×105t

These oil sludges not only contain a large amount of oil resources, but also contain a large number of harmful and toxic substances. If they are not treated properly, they will not only waste a lot of resources, but also cause serious environmental pollution. In China, in response to the problem of oil sludge generated by various production processes in enterprises, relevant departments of China have jointly formulated standards to require enterprises to pay sewage charges of 1,000 yuan/t while discharging sludge, which not only greatly increases the production cost of enterprises. At the same time, it also limits the serious harm to the environment caused by enterprises in pursuit of their own interests. Therefore, the harmless and resource-removing treatment of oil sludge is imminent.

China has successively issued the “Hazardous Waste Incineration Pollution Control Standards” (GB18484-2001) and the “Hazardous Waste Landfill Pollution Control Standards” (GB18598-2001) and other standards, and the corresponding regulations to require the corresponding responsible party must be on the oil sludge. It is treated to achieve its harmlessness in the “Technical Specification for Pollution Control of Waste Mineral Oil Recycling”, oil sludge with oil content > 5% must be recycled. In GB4284-84 “Contamination Standard for Pollutants in Agricultural Sludge” In the case of sludge that can be used in farmland, there is a clear requirement that the content of mineral oil should not exceed 3000 mg/kg.

The oil sludge pyrolysis gasification unit independently researched and developed by LCDRI has the advantages of precise automation control, safe and reliable system operation, high dry distillation efficiency, etc. Through the resource treatment of oil sludge, gas-liquid solid three-phase separation, extract oil products of oil sludge to achieve a win-win situation for resource recovery and environmental protection. The oil sludge decontamination gasification unit will become a general trend of oil sludge treatment for the harmless, resource treatment and utilization of oil sludge.

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