With the continuous improvement of economic level and the rapid development of science and technology, the pace of urbanization is gradually accelerating. Many problems have been exposed in this process. The severity of the pollution problem is constantly rising, and urban waste as a major obstacle to economic development cannot be ignored. In response to this situation, the relevant departments should apply waste incineration power generation technology and reuse the waste. This will not only solve the problem of pollution, but also speed up environmental construction.

1. Treatment methods and comparison of urban domestic garbage

The current methods of garbage disposal in China are diversified, including incineration, plasma gasification, composting and landfilling. For developed countries that have developed well in environmental construction, such as Japan, Germany, and Singapore, the main method used to deal with urban garbage is the incineration method. Current treatment methods for municipal solid waste:

(1) Waste incineration method: After sorting the collected garbage, the combustible garbage is poured into an incinerator for incineration. The waste incineration method can burn a large amount of bacteria, viruses and other harmful substances attached to the garbage through high temperature combustion, and use related equipment to recover heat energy for power generation and heating. At present, this technical method is being continuously improved, and it is the most effective method to achieve the goal of “reduction, resource utilization and harmlessness” of waste disposal;

(2) Plasma gasification method: Use hot plasma to gasify the garbage, then separate the organic and inorganic substances in the gasified garbage, and then use relevant technologies to refine it to achieve the purpose of recycling resources. The idea of ​​the plasma gasification method is good, but due to the limitations of China’s scientific and technological level, this method is not yet mature enough and has few applications;

(3) Compost method: refers to the use of microorganisms to degrade organic matter in garbage under artificial conditions to form humus-like substances that can be used to make fertilizers. This method has strong limitations. It is only suitable for organic waste and cannot be recycled. Therefore, the domestic market is relatively small and the profit is not high.

(4) Landfill method: refers to burying garbage in the soil, using microorganisms and other means in the soil to degrade the garbage, decomposing organic matter therein, and achieving the purpose of treating the garbage. In China, this is the main method of waste disposal, and the number and efficiency of landfills are increasing year by year. However, this method of treatment can only solve the temporary difficulties, and it will leave many future problems. For example, a large amount of garbage is buried in the soil, which will cause land pollution, affect farmland cultivation, and even cause infectious diseases. This is a discouraged practice.

At present, after the acceleration of urbanization in cities in China, the amount of garbage has skyrocketed to form a “garbage siege” situation. There are landfill, incineration, and compost methods for domestic garbage disposal in China. Landfill is still the main method. According to the amount of domestic waste treated by different types of waste disposal methods in the “China Urban Construction Statistical Yearbook” issued by the Ministry of Housing and Urban-Rural Development, landfills account for 64% of domestic waste disposal in China; followed by incineration, accounting for 38%. As of the end of 2018, there were 943 domestic waste treatment facilities in China, of which 657 were landfills, accounting for 70%.

2. Technical characteristics of waste incineration power generation

With the rapid development of science and technology, the understanding of waste incineration has also achieved innovation. Relying on the construction of incinerators can transform harmful substances in urban waste into harmless substances. After various types of pathogens have been eliminated, air pollution can be alleviated. . Waste incineration power generation means the waste heat from waste incineration is used for power generation and power supply.

The incineration method can oxidize combustibles in the garbage under high temperature oxidation to convert it into water and carbon dioxide. During the incineration process, a large amount of thermal energy will be released from the garbage. After being converted into a gas or solid form, the volume reduction and harmless treatment of the garbage can be realized. The waste incineration method has flexible site selection, simple operation, short treatment period, and can effectively decompose harmful substances.

Incineration requires a certain low calorific value of the garbage, so all garbage cannot be incinerated, and garbage that cannot be recycled but has a certain value can play the most scientific and effective role as the object of incineration. In addition, the flue gas formed in the incineration must be purified and digested, and the debris generated by the incineration must be digested, and there will be a lot of cost consumption in the purification and digestion. Therefore, there is a certain shortcoming in the waste treatment only by the incineration method. Utilize thermal energy to ensure optimal use of resources.

3. Waste incineration power generation process

As far as the waste incineration power generation process is concerned, it mainly includes the following six points:

(1) Garbage storage

There are many types of substances in urban garbage, and some garbage is also mixed with harmful substances. Therefore, it is necessary to pick out harmful and unburnable garbage during the treatment process, and transfer the remaining available garbage to the garbage storage tank after weighing. The rubbish storage tank can usually store the garbage disposal capacity for nearly a week, and the rubbish stored in the storage tank requires not only stirring and crushing, but also collecting garbage leachate;

(2) Waste incineration

After the garbage has been treated in the previous step, it can be transported towards the incinerator under the use of machinery and equipment, and the garbage can be incinerated. After the incineration is completed, the generated slag needs to be cleaned up. Incinerators include grate furnaces, circulating sulfurized bed furnaces, etc., there are certain differences in the corresponding incineration methods of each incinerator;

(3) Waste heat power generation

In addition to the incinerator, the equipment used in waste incineration power generation technology also involves turbine generators and waste heat boilers. After the incineration of waste is completed in the incinerator, after the heat generated by the waste heat boiler is converted, steam will be formed, and the turbine generator set can generate electricity by using the steam;

(4) Flue gas purification and treatment

After the incineration of garbage, a large amount of harmful substances will be generated, such as heavy metals and soot formed during the incineration of garbage. If such harmful substances cannot be properly handled, the environment will be polluted again. Flue gas purification treatment can be divided into three types of treatment methods: wet reaction tower with bag dust collector, dry reaction tower with bag dust collector, and semi-dry reaction tower with bag dust collector.

(5) Treatment of landfill leachate

Garbage is stored in the garbage storage tank, and after the fermentation, landfill leachate will be generated. These liquids contain more heavy metals and ammonia nitrogen, and they emit an odor. About 1/10 of the total weight of garbage. Leachate can only be discharged after sewage treatment, otherwise the environment will be polluted;

(6) Slag and ash treatment

After the incinerator burns the garbage, slag is generated. After processing slag with advanced technology, it can be used for daily production. After the slag is processed, it can be used as a material for making bricks or used in road paving. Because the dust collected by the bag filter has no use value, it should be landfilled after special harmless treatment.

4. Choice of waste incineration technology

(1) Pyrolysis gasification incinerator

Pyrolysis gasification incinerator belongs to controlled air combustion technology, and the system area includes heating and drying, pyrolysis gasification, residual carbon combustion, and combustible combustion. The advantages of pyrolysis gasification incinerator include simple equipment structure, low nitrogen oxide content in flue gas, and easy maintenance. Its disadvantages are its inability to adapt to high-moisture, low-calorific-value waste incineration, insufficient equipment processing capacity, and low heat recovery.

(2) Fluidized bed incinerator

The fluidized bed combustion technology means that domestic waste and sulfurized carriers are transferred to the incinerator through the upper part of the fluidized bed at a certain ratio. Under the action of sulfurized carriers, the garbage will violently tumbling in the furnace, and due to the circulation flow, it will In a suspended combustion state. This type of process usually consists of a circulating fluidized bed, a rotating fluidized bed, and a bubbling fluidized bed, among which the circulating fluidized bed has been widely used in China.

The advantages of circulating fluidized bed incinerators include compact structure, low investment, stable operation, less nitrogen oxide generation, and strong combustion adaptability. Its disadvantages are that it needs to add coal and pre-treat garbage, it takes up a lot of land and will affect the environment. It will generate excessive fly ash and power consumption, and there is a serious problem of heating surface wear.

(3) Rotary kiln incinerator

Under the continuous and slow rotation of the drum of the furnace body, the technology can transfer the garbage in the lower part of the cylinder toward the upper part of the cylinder through the rolling of the cylinder by means of the inner wall high temperature resistant plate, and then the garbage falls by its own weight. It is difficult to burn domestic waste with high moisture content and low heat value. Rotary kiln incinerators have the advantages of stable operation and good fuel adaptability, but their disadvantages are that the kiln body is longer, a post-combustion chamber is required, the investment is high, and the area is large.

(4) Mechanical grate incinerator

Mechanical grate incinerator technology occupies about 80% of the international market and is relatively mature. In combination with the specific form of the grate, it is mainly composed of a chain grate, a rolling grate, and a reciprocating grate. Among them, the reciprocating grate is composed of a backward push tilt reciprocating grate and a forward push tilt reciprocating grate. This type of furnace technology operates stably and can effectively turn and stir garbage under the grate mechanical movement, which helps to achieve the complete combustion of garbage.

The advantages of mechanical grate furnaces mainly include higher operating reliability, single processing capacity, no pre-treatment of garbage, no excessive flue gas emissions, low ash and slag production, no coal combustion, and low heating surface wear. . The disadvantage is that it has high grate processing accuracy, control requirements, high operating costs and investment, and subsequent maintenance and overhaul involves a large workload.

In summary, waste incineration power generation technology can optimize the use of originally worthless waste. Under the increasingly large-scale waste classification and treatment, incinerator technology has also ushered in more significant development, effectively improving the efficiency of incineration power generation, and economic benefits have been correspondingly improved. Under the increasing popularity of waste incineration power generation technology, it has further promoted the development of incineration power generation enterprises in China.

Solid waste treatment technology involves physics, chemistry, biology, mechanical engineering and other disciplines. The main treatment technologies are as follows:

(1) Pretreatment of solid waste.

Before the comprehensive utilization and final treatment of solid waste, pretreatment is often needed to facilitate the next treatment. Pretreatment mainly includes crushing, screening, grinding, compression and other processes of solid waste

(2) Physical treatment of solid waste.

Use the physical and physicochemical properties of solid waste to separate useful or harmful substances. According to the characteristics of solid waste, gravity separation, magnetic separation, electric separation, photoelectric separation, ballistic separation, friction separation and flotation can be used.

(3) Chemical treatment of solid waste.

Recovery of useful materials and energy through chemical conversion of solid waste. Calcination, roasting, sintering, solvent leaching, thermal decomposition, incineration and electric radiation are all chemical treatment methods.

(4) Biological treatment of solid waste.

Use the function of microorganism to treat solid waste. The basic principle is to use the biochemical action of microorganisms to decompose complex organic matters into simple substances and transform toxic substances into non-toxic substances. Biogas fermentation and composting belong to biological treatment.

(5) Final treatment of solid waste.

Hazardous solid waste with no use value needs to be finally treated. The final treatment methods include incineration, landfill and marine disposal. Solid wastes need to be treated innocuously before they are landfilled and dumped into the ocean.

The long-term storage of oil sludge will cause serious pollution to the surrounding soil, air and water, and even harm the health of the nearby residents.

The soil polluted by oil sludge may appear the phenomenon of insufficient nutrition, and oil sludge will restrict the growth of crops, hinder the germination of crop seeds, and even directly lead to the withering of crops. Due to the high viscosity of oil sludge, it will be adsorbed on the mineral tissue surface of the soil, which will eventually lead to the poor water holding capacity of the soil, and most of the harmful components in oil sludge can not be naturally degraded, which will exist in the soil for a long time.

After the pollution of soil by oil sludge, the organic branches gradually migrate and infiltrate into the groundwater. With the flow of groundwater, other water resources such as rivers and lakes are polluted and gradually accumulated.

If the nearby residents drink the polluted water or eat the polluted fish and shrimp, it will have a serious impact on their health. In particular, once PAHs in oil sludge enter the human body through food and drinking water, they will cause kidney and liver lesions and induce cancer.

As early as January 1996, due to the potential harm of oil sludge to the environment and human body, the law of the people’s Republic of China on the prevention and control of environmental pollution from solid waste and the law of the people’s Republic of China on the promotion of cleaner production clearly stipulated that oil sludge must be treated innocuously.

1. Sludge combustion power generation

The sludge (after mechanical dehydration) is first dried by heat, and then burned in the fluidized bed furnace to generate high-pressure steam, so as to promote the comprehensive system of steam engine power generation. Compared with the incineration system, the annual treatment of 95000 tons of dry sludge can save 60% of the capital. It can be seen that burning sludge for power generation is also an effective way for comprehensive utilization of sludge.

2. Low temperature pyrolysis of sludge to fuel oil

Low temperature pyrolysis of sludge is a technology to produce sludge derived fuel by using the organic matter in sludge during partial pyrolysis under heating conditions. After this process, sludge is converted into oil, carbon and gas with superior combustion characteristics. This technology is a process of energy self-sufficiency, and effectively controls the emission of heavy metals, so it has a broad application prospect.

The best way to dispose sludge is to make use of resources. It can not only dispose sludge, but also make full use of its precious resources. It can find a reasonable way to turn harm into profit and turn waste into treasure for sludge disposal and treatment of sewage treatment plant, and realize the synchronous growth of economic benefits and social benefits. Sludge building material utilization and combustion power generation can not only solve the problem of sludge outlet, but also save a lot of land area, which is a promising sludge disposal method suitable for China’s national conditions. In view of the research and utilization problems involved in sludge land use, in order to achieve the goal of safety and effectiveness, the government needs to organize the environmental protection department and the agricultural department to carry out scientific research on sludge land use in a planned way, and use sludge in the principle of economy, safety, rationality, effectiveness and benefit, so as to play its huge economic, social and ecological benefits.

Industrial wastewater refers to the wastewater, sewage and waste liquid produced in the industrial production process, which contains industrial production materials, intermediate products and products that are lost with the water and pollutants generated during the production process. It summarizes the chemical industrial wastewater and the printing and dyeing industrial wastewater. 15, paper industry wastewater, dye production wastewater, food industry wastewater and pesticide wastewater treatment process of 15 industrial wastewater.

1. Desulfurization wastewater from coal-fired power plants

Most desulfurization devices in power plants use flue gas limestone-gypsum wet desulfurization process. The process is mainly composed of a limestone slurry preparation system, a gypsum dehydration system, and a desulfurization wastewater treatment system. The water in the slurry of the desulfurization device will be enriched with heavy metal elements and Cl- in the process of continuous circulation. On the one hand, it accelerates the corrosion of the desulfurization equipment, on the other hand, it affects the quality of gypsum, and it is necessary to discharge the wastewater in a timely manner.

Desulfurization wastewater treatment process of power plant: desulfurization wastewater → wastewater tank → wastewater pump → pH neutralization tank → sedimentation tank → flocculation tank → clarifier → outlet tank → outlet pump → discharge to standard The desulfurization wastewater treatment system includes three parts: wastewater treatment, dosing, and sludge treatment. The waste water treatment system is mainly composed of waste water tanks, triple tanks, clarifiers, sludge pumps, outlet tanks, clean water pumps, fans, dehydrators and other equipment. In addition to a large amount of Cl-, Mg2 +, the impurities in the desulfurization wastewater also include: fluoride, nitrite, etc .; heavy metal ions, such as: Cu2 +, Hg2 +, etc .; insoluble CaSO4 and fine dust. In order to meet the wastewater discharge standards, corresponding wastewater treatment devices are required.

2. Chemical industry wastewater

Chemical industry wastewater mainly comes from: petrochemical industry, coal chemical industry, acid and alkali industry, chemical fertilizer industry, plastic industry, pharmaceutical industry, dye industry, rubber industry and other industrial wastewater.

The main measures for the prevention and control of chemical wastewater pollution are: first of all, production processes and equipment should be reformed to reduce pollutants, prevent waste water from being discharged, and be comprehensively used and recycled; waste water that must be discharged should be selected according to water quality and requirements.

The primary treatment mainly separates suspended solids, colloids, oil slicks or heavy oils in water. Water quality and quantity adjustment, natural sedimentation, floating and oil separation can be used.

The secondary treatment is mainly to remove biodegradable organic dissolved matter and some colloids, and to reduce the biochemical oxygen demand and some chemical oxygen demand in the wastewater. Biological treatment is usually adopted. A considerable amount of COD remains in the biologically treated wastewater, sometimes with high color, odor, and odor, or because of high environmental hygiene standards, a tertiary treatment method is required for further purification.

Tertiary treatment is mainly to remove organic pollutants and soluble inorganic pollutants that are difficult to biodegrade in wastewater. Common methods include activated carbon adsorption and ozone oxidation, and ion exchange and membrane separation technologies can also be used. Various chemical industry wastewater can choose different treatment methods according to different water quality, water quantity and external drainage quality requirements after treatment.

3. Printing and dyeing industry wastewater

The printing and dyeing industry has a large amount of water, and usually consumes 100 ~ 200t of water per 1t of printing and dyeing. 80% ~ 90% are discharged as printing and dyeing wastewater. Common treatment methods are recycling and harmless treatment.

Recycling: Wastewater can be recycled separately according to the characteristics of water quality, such as the diversion of bleaching and cooking wastewater and dyeing and printing wastewater. The former can be washed by convection. Multiple uses of one water can reduce the discharge;

The lye is recovered and reused, usually by evaporation method. If the amount of lye is large, it can be recovered by three-effect evaporation. If the amount of lye is small, it can be recovered by thin film evaporation.

Dye recovery, such as Shihlin dye can be acidified into cryptobasic acid, showing colloidal particles. Suspended in the residual liquid, it can be recycled after filtration.

Harmless treatment can be divided into physical treatment methods such as precipitation method and adsorption method. The precipitation method mainly removes suspended matter in wastewater; the adsorption method mainly removes dissolved pollutants and decoloration in wastewater.

Chemical treatment methods include neutralization, coagulation and oxidation. The neutralization method consists in adjusting the pH of the wastewater, and can also reduce the color of the wastewater. The coagulation method consists in removing the dispersed dyes and colloidal substances in the wastewater. The oxidation method consists in oxidizing the reducing substances in the wastewater to precipitate the sulfur dyes and reducing dyes.

Biological treatment methods include activated sludge, biological turntable, biological drum and biological contact oxidation method. In order to improve the quality of the effluent water and meet discharge standards or recycling requirements, it is often necessary to use several methods for joint treatment.

4. Wastewater from the paper industry

Papermaking wastewater mainly comes from the two processes of pulping and papermaking in the paper industry. Pulp is the process of separating fibers from plant raw materials to make pulp, which is then bleached; papermaking is to dilute, shape, squeeze, and dry the pulp to make paper. Both processes discharge large amounts of wastewater.
Polluted wastewater is the most severely polluted. The waste water discharged during washing is dark brown, which is called black water. The concentration of pollutants in black water is very high, BOD is as high as 5 ~ 40g / L, and it contains a large amount of fiber, inorganic salts and pigments. Wastewater from the bleaching process also contains a large amount of acid and alkali substances. The waste water discharged from the paper machine is called white water, which contains a large amount of fiber and fillers and rubber added during the production process.

Wastewater treatment of the paper industry should focus on improving the recycling rate, reducing water consumption and wastewater discharge. At the same time, we should actively explore a variety of reliable, economical and able to make full use of useful resources in wastewater treatment methods. For example, the flotation method can recover fibrous solid matter in white water with a recovery rate of 95% and the clarified water can be reused; the combustion method can recover sodium hydroxide, sodium sulfide, sodium sulfate, and other sodium salts combined with organic matter in black water.

Neutralization method to adjust the pH value of wastewater; coagulation sedimentation or flotation method can remove suspended solids in wastewater; chemical precipitation method can decolorize; biological treatment method can remove BOD, which is more effective for kraft paper wastewater; wet oxidation method is more effective success. In addition, there are also domestic and foreign treatment methods such as reverse osmosis, ultrafiltration, and electrodialysis.

5.Dye production wastewater

Dye production wastewater contains acids, alkalis, salts, halogens, hydrocarbons, amines, nitro compounds, dyes and their intermediates, and some also contain pyridine, cyanide, phenol, benzidine, and heavy metals mercury, cadmium, and chromium. The components of these wastewaters are complex, toxic and difficult to treat. Therefore, the treatment of dye production wastewater should be based on the characteristics of the wastewater and its discharge requirements. Select an appropriate treatment method.

6. Food industry wastewater

The food industry has a wide range of raw materials and a wide range of products. The amount and quality of discharged wastewater varies widely.
The main pollutants in wastewater are: solid substances floating in wastewater, such as vegetable leaves, peels, minced meat, poultry feathers, etc .; the substances suspended in wastewater include oil, protein, starch, colloidal substances, etc .; acids dissolved in wastewater , Alkali, salt, sugar, etc .; mud and other organic matter entrained by raw materials; etc .;

Food industry wastewater is characterized by high organic matter and suspended matter content, easy to spoil, and generally has no major toxicity. Its harm is mainly to make the water body eutrophic, which will cause the death of aquatic animals and fish, promote the odor of organic matter deposited on the bottom of the water, deteriorate the water quality and pollute the environment.

In addition to proper pretreatment according to water quality characteristics, the wastewater treatment in the food industry is generally suitable for biological treatment. If the quality of the effluent is very high or the organic matter content in the wastewater is high, a two-stage aeration tank or a two-stage biological filter, or a multi-stage biological turntable can be used. Or two types of biological treatment devices can be used in combination, or anaerobic can be used. -Aerobic series.

7. Pesticide wastewater

There are many types of pesticides, and the quality of pesticide wastewater is complex. Its main characteristics are: high concentration of pollutants, chemical oxygen demand (COD) can reach tens of thousands of milligrams per liter; high toxicity, in addition to pesticides and intermediates in wastewater, toxic substances such as phenol, arsenic, mercury and many other Bio-degradable substances; foul odor, irritating to the human respiratory tract and mucous membranes; water quality and quantity are unstable.

Therefore, the pollution of pesticide wastewater to the environment is very serious. The purpose of pesticide wastewater treatment is to reduce the concentration of pollutants in pesticide production wastewater, improve the recycling rate, and strive to achieve harmlessness. Pesticide wastewater treatment methods include activated carbon adsorption method, wet oxidation method, solvent extraction method, distillation method and activated sludge method. However, the development of new pesticides with high efficiency, low toxicity and low residue is the development direction of pesticides.

8.Cyanide-containing wastewater

The cyanide-containing wastewater mainly comes from electroplating, coal gas, coking, metallurgy, metal processing, chemical fiber, plastic, pesticide, chemical and other departments.

Cyanide-containing wastewater is a relatively toxic industrial wastewater. It is unstable in water and easily decomposes. Inorganic cyanide and organic cyanide are highly toxic substances. Human ingestion can cause acute poisoning. The lethal amount of cyanide to the human body is 0.18g, the potassium cyanide is 0.12g, and the mass concentration of cyanide to fish in water is 0.04 ~ 0.1mg / L.

The cyanide-containing wastewater treatment measures mainly include: reforming the process to reduce or eliminate effluent cyanide-containing wastewater. If cyanide-free electroplating is used, industrial wastewater in electroplating workshops can be eliminated. Wastewater with high cyanide content should be recycled. Wastewater with low cyanide content should be purified before being discharged. Recovery methods include acidification aeration-alkali solution absorption method, steam desorption method, and the like.

The treatment methods include alkaline chlorination method, electrolytic oxidation method, pressure hydrolysis method, biochemical method, biological iron method, ferrous sulfate method, and air stripping method. Among them, the alkaline chlorination method is widely used, the ferrous sulfate method is incomplete and unstable, and the air stripping method pollutes the atmosphere and the effluent does not meet the discharge standards. Less adopted.

9.Phenol-containing wastewater

Phenol-containing wastewater mainly comes from coking plants, gas plants, petrochemical plants, insulation materials plants and other industrial sectors, as well as the production of ethylene, synthetic phenol, polyamide fibers, synthetic dyes, organic pesticides and phenolic resins from petroleum cracking. The phenol-containing wastewater mainly contains phenol-based compounds, which are a protoplasmic toxicant that can solidify proteins.

10. Mercury-containing wastewater

Mercury-containing wastewater mainly comes from non-ferrous metal smelters, chemical plants, pesticide plants, paper mills, dye plants and thermal instrumentation plants. The toxicity of various mercury compounds is very different, such as methylmercury, methylmercury is easily absorbed into the human body, not easily degraded, excreted very slowly, and easily accumulated in the brain.

11.Heavy metal wastewater

The heavy metal wastewater mainly comes from the wastewater from mining, smelting, electrolysis, electroplating, pesticide, medicine, paint, pigment and other enterprises. The types, contents and existing forms of heavy metals in wastewater vary with different production enterprises.

The principle of heavy metal wastewater treatment is: the most fundamental is to reform the production process without using or reducing the use of toxic heavy metals; followed by the use of reasonable technological processes, scientific management and operation to reduce the amount of heavy metals and the amount of waste with wastewater, and minimize efflux Amount of wastewater. Heavy metal wastewater should be treated in situ at the place of production and mixed with other wastewater to avoid complicating the treatment. Moreover, it should not be discharged directly into urban sewers without treatment, so as to avoid expanding heavy metal pollution.

The treatment of heavy metal wastewater can generally be divided into two categories: one is to convert the heavy metals in the wastewater in a dissolved state into insoluble metal compounds or elements and remove them from the wastewater by precipitation and floating. Applicable methods such as neutralization precipitation method, sulfide precipitation method, floating separation method, electrolytic precipitation (or floating) method, diaphragm electrolysis method, etc .; second, the heavy metals in the wastewater are concentrated without changing their chemical form and For separation, applicable methods include reverse osmosis, electrodialysis, evaporation, and ion exchange. These methods should be used alone or in combination according to the quality and quantity of wastewater.

12. Metallurgical wastewater

The main characteristics of metallurgical wastewater are large water volume, many types, and complex and variable water quality. According to the source and characteristics of wastewater, there are mainly cooling water, pickling wastewater, washing wastewater (dust removal, gas or flue gas), slag washing wastewater, coking wastewater, and wastewater condensed, separated or overflowed during production.

The development trend of metallurgical wastewater treatment is to develop and adopt new processes and technologies that use no or little water and no pollution or pollution. Develop comprehensive utilization technologies, such as recovering useful substances and heat energy from waste water and waste gas, and reducing material and fuel loss; according to different water quality requirements, comprehensively balance and use in series, while improving water quality stabilization measures, and continuously improving water cycle utilization; The new treatment technology and technology of metallurgical wastewater characteristics, such as magnetic steel treatment of steel wastewater, has the advantages of high efficiency, small footprint, convenient operation and management.

13. Acid and alkali wastewater

Acid wastewater mainly comes from steel plants, chemical plants, dye plants, electroplating plants and mines, etc., which contains various harmful substances or heavy metal salts. The mass fractions of acids vary widely, ranging from less than 1% to as high as 10%.

Alkaline wastewater mainly comes from printing and dyeing plants, leather mills, paper mills, and oil refineries. Some of them contain organic bases or inorganic bases. Some of the mass fractions of alkali are higher than 5% and some are lower than 1%. In addition to acid-base wastewater, acid-base wastewater often contains acid salts, basic salts, and other inorganic and organic substances.
Acid-alkali wastewater is highly corrosive and can only be discharged after proper treatment.

The general principle for treating acid-alkali wastewater is: high-concentration acid-alkali wastewater should be prioritized for recycling. According to water quality, water volume and different process requirements, carry out plant or regional scheduling and try to reuse as much as possible: if reuse is difficult, or the concentration is too high Low, large amount of water, can be concentrated to recover acid and alkali.

Low-concentration acid and alkali wastewater, such as the washing water of the pickling tank and the rinse water of the alkali cleaning tank, should be neutralized.

For neutralization treatment, the principle of treating waste with waste should be considered first. Such as acid and alkaline wastewater neutralize each other or use waste alkali (slag) to neutralize acidic wastewater, use waste acid to neutralize alkaline wastewater. In the absence of these conditions, a neutralizing agent can be used.

14.Beneficiation wastewater

Beneficiation wastewater has the characteristics of large water volume, high suspended matter content, and many types of harmful substances. Its harmful substances are heavy metal ions and ore dressing agents. Heavy metal ions include copper, zinc, lead, nickel, barium, cadmium, and arsenic and rare elements.

The beneficiation wastewater is mainly passed through the tailings dam to effectively remove suspended matter in the wastewater, and the content of heavy metals and flotation reagents can also be reduced. If the discharge requirements are not met, further treatment should be carried out. Common treatment methods are: lime neutralization and roasted dolomite adsorption can be used to remove heavy metals; ore adsorption method and activated carbon adsorption method can be used as the main removal flotation agent; Cyanide wastewater can be chemically oxidized.

15. Oily wastewater

Oily wastewater mainly comes from industrial sectors such as petroleum, petrochemicals, iron and steel, coking, gas generation stations, and mechanical processing. Except for heavy tars with a relative density of 1.1 or higher, the remaining relative density of oily pollutants in the wastewater is less than 1. Oily substances usually exist in three states in wastewater.

Floating oil, the diameter of the oil droplets is larger than 100 μm, and it is easy to separate from the waste water.

Disperse the oil, the diameter of the oil droplets is between 10 and 100 μm, and float in water.

Emulsified oil, the diameter of the oil droplets is less than 10 μm, and it is not easy to separate from the wastewater.

Due to the large differences in oil concentration in wastewater discharged from different industrial sectors, such as wastewater generated during the refining process, the oil content is about 150 ~ 1000mg / L, the tar content in coking wastewater is about 500 ~ 800mg / L, and the wastewater from the gas generation station is discharged into the wastewater. The tar content can reach 2000 ~ 3000mg / L.

Therefore, the treatment of oily wastewater should first use an oil trap to recover oil slicks or heavy oil. The treatment efficiency is 60% to 80%, and the oil content in the effluent is about 100 to 200mg / L. Emulsified and dispersed oil in wastewater is difficult. Treatment, it should prevent or reduce the emulsification phenomenon.

The first is to reduce the emulsification of oil in wastewater during the production process;

The second is to minimize the number of times the pump is used to raise the wastewater during the treatment process, so as not to increase the degree of emulsification. Treatment methods usually use air flotation and demulsification.