Do you know the characteristics and treatment methods of industrial wastewater?

Industrial waste

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 lost with water, as well as pollutants generated in the production process. Common industrial wastewater and its characteristics are as follows: Category:

 

1. Characteristics and treatment process of desulfurization wastewater from coal-fired power plants

Features of desulfurization wastewater from power plants:

Most desulfurization devices in power plants use flue gas limestone-gypsum wet desulfurization process. The process is mainly composed of limestone slurry preparation system, gypsum dehydration system and desulfurization wastewater treatment system. In the process of continuous circulation, the water in the slurry of the desulfurization unit will be enriched with heavy metal elements and Cl-, etc., on the one hand, it will accelerate the corrosion of the desulfurization equipment, and on the other hand, it will affect the quality of gypsum, and the wastewater needs to be discharged in time.

 

Power plant desulfurization wastewater treatment process

Power plant desulfurization wastewater treatment process: desulfurization wastewater→wastewater tank→wastewater pump→pH neutralization tank→settling tank→flocculation tank→clarifier→outlet tank→outlet pump→standard discharge

 

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 tank, triple box, clarifier, mud pump, water outlet tank, clean water pump, fan, dehydrator and other equipment. In addition to a large amount of Cl- and Mg2+, impurities in 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: production wastewater discharged from petrochemical industry, coal chemical industry, acid and alkali industry, fertilizer industry, plastic industry, pharmaceutical industry, dye industry, rubber industry, etc.

 

The main measures for the prevention and control of chemical wastewater pollution are: first, the production process and equipment should be reformed, pollutants should be reduced, waste water should be prevented from being discharged, and comprehensive utilization and recycling should be carried out; the treatment level of waste water that must be discharged should be selected according to the water quality and requirements.

 

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

 

Secondary treatment is mainly to remove biodegradable organic dissolved substances and some colloidal substances, and reduce the biochemical oxygen demand and part of the chemical oxygen demand in wastewater, usually by biological treatment. A considerable amount of COD remains in the biologically treated wastewater, sometimes with high color, smell and taste, or due to high environmental sanitation standards, tertiary treatment methods are required for further purification.

 

The tertiary treatment is mainly to remove organic pollutants and dissolved inorganic pollutants that are difficult to biodegrade in wastewater. Commonly used methods are activated carbon adsorption method and ozone oxidation method, and ion exchange and membrane separation technology can also be used. Various chemical industry wastewater can choose different treatment methods according to the requirements of different water quality, water quantity and external drainage quality after treatment.

 

3. Printing and dyeing industrial wastewater

The printing and dyeing industry consumes a lot of water, usually 100-200t of water per 1t of printing and dyeing textiles. Of which 80%-90% is discharged as printing and dyeing wastewater. Commonly used treatment methods include recycling and harmless treatment.

 

recycle and re-use:

Wastewater can be recycled according to the characteristics of water quality, such as the diversion of bleaching and refining wastewater and dyeing and printing wastewater. The former can be washed by convection. One water is used for multiple purposes, reducing discharge;

 

The recovery and utilization of lye is usually recovered 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;

 

Recycling of dyes. For example, Shihlin dyes can be acidified into cryptic acid in the form of colloidal particles. They are suspended in the residual liquid and recycled after precipitation and filtration.

 

Harmless treatment:

Physical treatment methods include precipitation method and adsorption method. The precipitation method mainly removes the suspended solids in the wastewater; the adsorption method mainly removes the dissolved pollutants and decolorization in the wastewater.

 

Chemical treatment methods include neutralization, coagulation and oxidation. The neutralization method is to adjust the acidity and alkalinity in the wastewater, and it can also reduce the chromaticity of the wastewater; the coagulation method is to remove disperse dyes and colloidal substances in the wastewater; the oxidation method is to oxidize the reducing substances in the wastewater to precipitate sulfur dyes and vat dyes.

 

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

 

4. Paper industry wastewater

Papermaking wastewater mainly comes from the two production processes of pulping and papermaking in the papermaking industry. Pulping is to separate the fibers from plant raw materials to make pulp, which is then bleached; papermaking is to dilute, shape, press, and dry the pulp to make paper. Both processes discharge large amounts of wastewater.

The wastewater produced by pulping is the most polluted. The wastewater discharged during pulp washing is dark brown, called black water. The concentration of pollutants in black water is very high, the BOD is as high as 5-40g/L, and it contains a lot of fibers, inorganic salts and pigments. The wastewater discharged from the bleaching process also contains a large amount of acid and alkali substances. The waste water from paper machines, known as white water, contains a lot of fibers and fillers and sizing materials added during the production process.

The treatment of paper industry wastewater should focus on increasing the rate of recycled water, reducing water consumption and wastewater discharge, and at the same time actively exploring various reliable, economical and fully utilizing the useful resources in wastewater treatment methods. For example, flotation method can recover fibrous solid matter in white water, the recovery rate can reach 95%, and clarified water can be reused; combustion method can recover sodium hydroxide, sodium sulfide, sodium sulfate and other sodium salts combined with organic matter in black water.

Neutralization method adjusts 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 in treating sulfite pulp wastewater success. In addition, there are also treatment methods such as reverse osmosis, ultrafiltration, and electrodialysis at home and abroad.

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 such as mercury, cadmium, and chromium. The composition of these wastewater is complex. It is toxic and difficult to handle. Therefore, the treatment of dye production wastewater should be based on the characteristics of the wastewater and its discharge requirements. An appropriate treatment method should be selected.

For example, to remove solid impurities and inorganic substances, coagulation and filtration methods can be used; to remove organic substances and toxic substances, chemical oxidation, biological and reverse osmosis methods are mainly used; decolorization can generally be composed of coagulation and adsorption methods. Process, the removal of heavy metals can use ion exchange method, etc.

6. Food industry wastewater

The food industry has a wide range of raw materials and a wide variety of products, and the amount and quality of discharged wastewater vary greatly.

The main pollutants in wastewater are:

Solid substances floating in wastewater, such as vegetable leaves, peels, minced meat, poultry feathers, etc.; substances suspended in wastewater include oil, protein, starch, colloidal substances, etc.; acids, alkalis, salts, sugars dissolved in wastewater etc.; silt and other organic matter entrained by raw materials; pathogenic bacteria, etc.

 

Food industry wastewater is characterized by high content of organic substances and suspended solids, easy to spoil, and generally not toxic. Its harm is mainly to make the water eutrophication, resulting in the death of aquatic animals and fish, and 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 the characteristics of water quality, biological treatment should generally be adopted in the treatment of food industry wastewater. If the quality of the effluent is very high or the organic content in the wastewater is very high, a two-stage aeration tank or a two-stage biological filter, or a multi-stage biological turntable, or a combination of two biological treatment devices, or an anaerobic treatment device can be used. - aerobic tandem.

 

7. Pesticide wastewater

There are many kinds of pesticides, and the water quality of pesticide wastewater is complex. Its main features are:

The concentration of pollutants is high, and the chemical oxygen demand (COD) can reach tens of thousands of mg per liter; the toxicity is high. In addition to pesticides and intermediates, the wastewater also contains toxic substances such as phenol, arsenic, mercury, and many substances that are difficult to degrade by organisms. ; odorous, irritating to human respiratory tract and mucous membranes; unstable water quality and quantity.

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, wet oxidation, solvent extraction, distillation and activated sludge.

However, the development of new pesticides with high efficiency, low toxicity and low residues is the development direction of pesticides. Some countries have banned the production of organochlorine and organomercury pesticides such as 666, and actively researched and used microbial pesticides, which is a new way to fundamentally prevent pesticide wastewater from polluting the environment.

8. Cyanide-containing wastewater

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

Cyanide-containing wastewater is a highly toxic industrial wastewater. It is unstable in water and easy to decompose. Both inorganic cyanide and organic cyanide are highly toxic substances, which can cause acute poisoning when ingested by humans. The lethal dose of cyanide to human body is 0.18, potassium cyanide is 0.12g, and the lethal mass concentration of cyanide to fish in water is 0.04~0.1mg/L.

The main treatment measures for cyanide-containing wastewater are:

Reform the process to reduce or eliminate the discharge of cyanide-containing wastewater. For example, the use of cyanide-free electroplating method can eliminate industrial wastewater from electroplating workshops.

Wastewater with high cyanide content should be recycled, and wastewater with low cyanide content should be purified and treated before being discharged. Recovery methods include acidification aeration - lye absorption method, steam desorption method, etc.

Treatment methods include alkaline chlorination method, electrolytic oxidation method, pressurized hydrolysis method, biochemical method, biological iron method, ferrous sulfate method, air stripping method, etc. Among them, the alkaline chlorination method is widely used, the ferrous sulfate method is not completely and unstable, and the air stripping method pollutes the atmosphere, and the effluent does not meet the emission standards. Less used.

9. Phenol-containing wastewater

Phenol-containing wastewater mainly comes from industrial sectors such as coking plants, gas plants, petrochemical plants, and insulating material plants, as well as the production process of petroleum cracking to produce ethylene, synthetic phenol, polyamide fibers, synthetic dyes, organic pesticides and phenolic resins. Phenol-containing wastewater mainly contains phenol-based compounds, which are protoplasmic poisons that can coagulate 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 varies greatly, such as methylmercury, which is easily absorbed into the human body, not easily degraded, excreted slowly, and easily accumulated in the brain.

11. Heavy metal wastewater

Heavy metal wastewater mainly comes from wastewater discharged 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 principles of heavy metal wastewater treatment are:

The most fundamental is to reform the production process and use no or less toxic heavy metals; the second is to adopt a reasonable process flow, scientific management and operation, reduce the amount of heavy metals and the loss with wastewater, and minimize the amount of wastewater discharged. Heavy metal wastewater should be treated on-site at the point of production and not mixed with other wastewater to avoid complicating treatment. It should not be directly discharged into urban sewers without treatment, so as not to expand heavy metal pollution.

The treatment of heavy metal wastewater can usually be divided into two categories:

One is to convert the dissolved heavy metals in the wastewater into insoluble metal compounds or elements, which are removed 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.;

The second is to concentrate and separate heavy metals in wastewater without changing their chemical forms. The applicable methods include reverse osmosis, electrodialysis, evaporation and ion exchange. These methods should be used individually or in combination according to the quality and quantity of wastewater.

12. Metallurgical wastewater

The main characteristics of metallurgical wastewater are large amount of water, many types, and complex and changeable 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 that is condensed, separated or overflowed from production.

The development trend of metallurgical wastewater treatment is:

Develop and adopt new processes and technologies with no or less water and no or less pollution, such as dry quenching, coking coal preheating, desulfurization and decyanation directly from coke oven gas, etc.; develop comprehensive utilization technologies, such as from Recover useful substances and heat energy from waste water and waste gas to reduce the loss of material and fuel; according to different water quality requirements, comprehensive balance, use in series, improve water quality stabilization measures, and continuously improve the recycling rate of water;

Develop new treatment processes and technologies suitable for the characteristics of metallurgical wastewater, such as magnetic treatment of iron and steel wastewater. It has the advantages of high efficiency, small footprint, and convenient operation and management.

13. Acid-base wastewater

Acid wastewater mainly comes from iron and steel plants, chemical plants, dye plants, electroplating plants and mines, etc., and contains various harmful substances or heavy metal salts. The mass fraction of acid varies widely, with lows less than 1% and highs greater than 10%.

Alkaline wastewater mainly comes from printing and dyeing factories, tanneries, paper mills, oil refineries, etc. Some of them contain organic bases or inorganic bases. The mass fraction of alkali is higher than 5%, and some is lower than 1%. In addition to acid and alkali, acid-base wastewater often contains acid salts, basic salts, and other inorganic and organic substances.

Acid-base wastewater is highly corrosive and needs to be properly treated before it can be discharged.

A general principle for the treatment of acid-base wastewater is:

High-concentration acid-base wastewater should be recycled and reused first. According to water quality, water volume and different process requirements, factory or regional scheduling should be carried out and reused as much as possible: if it is difficult to reuse, or the concentration is low and the water volume is large, concentration can be used. method to recover acid and alkali.

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

For neutralization treatment, the principle of treating waste with waste should be considered first. For example, acid and alkali waste water are neutralized with each other, or waste alkali (slag) is used to neutralize acid waste water, and waste acid is used to neutralize alkaline waste water. In the absence of these conditions, a neutralizing agent treatment can be employed.

14. Mineral processing wastewater

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

The flotation reagents added in the beneficiation process are as follows: collectors, such as xanthate (RocssMe), black medicine [(RO)2PSSMe], white medicine [CS(NHC6H5)2]; inhibitory agents, such as cyanide ( KCN, NaCN), water glass (Na2SiO3); foaming agent, such as turpentine, cresol (C6H4CH30H); active punishment, such as copper sulfate (CuS04), heavy metal salts; vulcanizing agent, such as sodium sulfide; mineral paddle conditioner, Such as sulfuric acid, lime, etc.

The beneficiation wastewater mainly passes through the tailings dam, which can effectively remove the suspended solids 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. The commonly used treatment methods are:

To remove heavy metals, lime neutralization method and roasting dolomite adsorption method can be used; ore adsorption method and activated carbon adsorption method can be used for the main removal flotation agent; chemical oxidation method can be used for cyanide-containing wastewater.

15. Oily wastewater

Oily wastewater mainly comes from petroleum, petrochemical, iron and steel, coking, gas generating stations, mechanical processing and other industrial sectors. The relative density of oil pollutants in wastewater is less than 1 except for heavy tar whose relative density is above 1.1. Oil substances generally exist in three states in wastewater.

When oil floats on the surface, the particle size of oil droplets is larger than 100 μm, which is easy to separate from wastewater. Dispersed oil. The particle size of oil droplets is between 10 and 100 μm, and they float in water. Emulsified oil, the particle size of oil droplets is less than 10μm, and it is not easy to separate from wastewater.

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

Therefore, the treatment of oily wastewater should first use the oil separator to recover floating oil or heavy oil. The treatment efficiency is 60% to 80%, and the oil content in the effluent is about 100 to 200 mg/L; the emulsified oil and dispersed oil in the wastewater are difficult Therefore, emulsification should be prevented or reduced.

One of the methods is to pay attention to reducing the emulsification of oil in the wastewater during the production process; the second is to minimize the number of times the wastewater is lifted with a pump during the treatment process, so as not to increase the degree of emulsification. The treatment methods are usually air flotation and demulsification.