Zero discharge of industrial wastewater treatment methods
Release time：
2020-07-16
Industrial wastewater discharge is one of the important factors that cause water quality safety problems. Failure to meet the standards of industrial wastewater treatment will cause serious consequences. Here is a brief introduction to some industrial wastewater treatment methods.
Industrial wastewater discharge is one of the important factors that cause water quality safety problems. Failure to meet the standards of industrial wastewater treatment will cause serious consequences. Here is a brief introduction to some industrial wastewater treatment methods.
Phenolic wastewater
Phenol-containing wastewater mainly comes from industrial sectors such as coking plants, gas plants, petrochemical plants, insulating materials plants, and 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, such as phenol, cresol, xylenol and nitrocresol. Phenol-based compounds are a kind of protoplasmic poison that can coagulate proteins.
When the mass concentration of phenol in the water reaches 0.1-0.2mg/L, the fish will have a peculiar smell and cannot be eaten; increasing the mass concentration to 1mg/L will affect fish spawning. If the phenol content is 5-10mg/L, the fish will be large death. Phenol in drinking water can affect human health. Even if the mass concentration of phenol in water is only 0.002mg/L, disinfection with chlorine will produce chlorophenol stench. Usually, the phenol-containing wastewater with a mass concentration of 1000mg/L is called high-concentration phenol-containing wastewater. This kind of wastewater must be recycled after phenol is processed.
Phenol-containing wastewater with a mass concentration of less than 1000mg/L is called low-concentration phenol-containing wastewater. Usually this kind of waste water is recycled and phenol is concentrated and recycled for treatment. Methods of recovering phenol include solvent extraction, steam stripping, adsorption, and closed circulation. Wastewater with a mass concentration of phenol below 300 mg/L can be treated by biological oxidation, chemical oxidation, physical and chemical oxidation and other methods before being discharged or recycled.
Mercury wastewater
The mercury-containing wastewater mainly comes from non-ferrous metal smelters, chemical plants, pesticide plants, paper mills, dye plants and thermal instrumentation plants. Methods for removing inorganic mercury from wastewater include sulfide precipitation, chemical coagulation, activated carbon adsorption, metal reduction, ion exchange, and microbiological methods. Generally, alkaline mercury-containing wastewater is usually treated by chemical coagulation or sulfide precipitation. Acidic mercury-containing wastewater can be treated by metal reduction. Low-concentration mercury-containing wastewater can be treated by activated carbon adsorption, chemical coagulation, or activated sludge. Organic mercury wastewater is more difficult to treat. Generally, organic mercury is oxidized to inorganic mercury and then treated.
The toxicity of various mercury compounds varies greatly. Elemental mercury is basically non-toxic; mercury in inorganic mercury is a highly toxic substance, and phenyl mercury in organic mercury decomposes quickly and is not very toxic; methyl mercury is easily absorbed when entering the human body, not easily degraded, and excreted very slowly, especially It is easy to accumulate in the brain. Very toxic, such as Minamata disease is caused by methylmercury poisoning.
Oily wastewater treatment
Oily wastewater mainly comes from industrial sectors such as petroleum, petrochemical, iron and steel, coking, gas generating stations, and mechanical processing. For oily pollutants in wastewater, the relative density of heavy tar is less than 1.1 except for heavy tar. Oily substances usually exist in three states in wastewater. (1) The oil floats, and the particle size of the oil droplets is greater than 100 μm, which is easy to separate from the wastewater. (2) Dispersed oil. The particle size of the oil droplets is between 10 and 100 μm, and they float in water. (3) Emulsified oil. The particle size of the oil droplets is less than 10μm, which is not easy to separate from the wastewater.
Because the oil concentration in wastewater discharged from different industrial departments is very different, such as wastewater generated in the oil refining process, the oil content is about 150-1000mg/L, the tar content in the coking wastewater is about 500-800mg/L, and the wastewater discharged from the gas generating station The tar content can reach 2000-3000mg/L.
Therefore, the treatment of oily wastewater should first use an oil trap 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; emulsified oil and dispersed oil in wastewater are difficult Treatment, it should prevent or reduce emulsification. One of the methods is to reduce the emulsification of oil in the wastewater during the production process; the second is to minimize the number of pumps to lift the wastewater during the treatment process to avoid increasing the degree of emulsification. The treatment method usually adopts air flotation method and demulsification method.
Heavy metal wastewater
Heavy metal wastewater mainly comes from wastewater discharged from enterprises such as mining, smelting, electrolysis, electroplating, pesticides, medicine, paint, and pigments. The type, content and existing form of heavy metals in wastewater vary with different manufacturers. Since heavy metals cannot be decomposed and destroyed, they can only transfer their location and change their physical and chemical forms.
For example, after chemical precipitation treatment, heavy metals in wastewater are transformed from dissolved ionic forms into insoluble compounds and precipitated, and transferred from water to sludge; after ion exchange treatment, heavy metal ions in wastewater are transferred to ion exchange resin After regeneration, it is transferred from the ion exchange resin to the regeneration waste liquid. Therefore, the principle of heavy metal wastewater treatment is: first, the fundamental is to reform the production process. Do not use or use less toxic heavy metals; secondly, use reasonable process, scientific management and operation to reduce the amount of heavy metals and the amount of waste water lost. Reduce the amount of wastewater discharged outside.
Heavy metal wastewater should be treated on-site at the place where it is produced, and mixed with other wastewater to avoid complicating the treatment. Moreover, it should not be discharged directly 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 heavy metals in the dissolved state of the wastewater into insoluble metal compounds or elements, which are removed from the wastewater by precipitation and floating. The applicable methods are neutralization precipitation, 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 form. The applicable methods are reverse osmosis , Electrodialysis, evaporation and ion exchange, etc. These methods should be used alone or in combination according to the wastewater quality and water volume.
Cyanide wastewater
Cyanide-containing wastewater mainly comes from electroplating, gas, coking, metallurgy, metal processing, chemical fiber, plastics, pesticides, and chemical industries. Cyanide-containing wastewater is a highly toxic industrial wastewater, which is unstable in water and easier to decompose. Both inorganic cyanide and organic cyanide are highly toxic substances, and human ingestion can cause acute poisoning. The lethal dose of cyanide to human body is 0.18, potassium cyanide is 0.12g, and the mass concentration of cyanide to fish in water is 0.04 to 0.1mg/L.
Cyanide-containing wastewater treatment measures mainly include: (1) Reform the process to reduce or eliminate the cyanide-containing wastewater discharged out. For example, the non-cyanide electroplating method can eliminate the industrial wastewater of the electroplating workshop. (2) Wastewater with high cyanide content should be recycled, and wastewater with low cyanide content should be purified 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, and the ferrous sulfate method is incomplete and unstable. The air blow-off method pollutes the atmosphere and the effluent does not meet the emission standards. It is rarely used.
Paper industry wastewater
Papermaking wastewater mainly comes from the pulping and papermaking processes in the papermaking industry. Pulping is to separate the fibers from plant raw materials into a slurry, and then bleach; papermaking is to dilute, shape, press, and dry the slurry to make paper. Both processes discharge large amounts of waste water. The pollution of wastewater from pulping is serious. The waste water discharged during washing is dark brown, called black water. The concentration of pollutants in the 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 discharged from the paper machine is called white water, which contains a large amount of fibers and fillers and rubber materials added in the production process. The treatment of wastewater from the papermaking industry should focus on increasing the recycling rate, reducing water consumption and wastewater discharge, and actively exploring various reliable, economical, and capable of making full use of useful resources in wastewater treatment methods.
For example, the flotation method can recover fibrous solids in white water, the recovery rate can reach 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 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 for sulfite pulp wastewater treatment success. In addition, treatment methods such as reverse osmosis, ultrafiltration, and electrodialysis are also used at home and abroad.
Printing and dyeing industrial wastewater
The printing and dyeing industry consumes a lot of water, usually 100 to 200 tons of water per 1 ton of textiles during the printing and dyeing process. 80% to 90% of it is discharged as printing and dyeing wastewater. Commonly used treatment methods include recycling and harmless treatment.
Recycling: (1) Waste water can be recycled and reused according to water quality characteristics, such as the diversion of bleaching and smelting wastewater and dyeing and printing wastewater. The former can be washed by convection. One water is used for multiple purposes, reducing emissions; (2) Lye recycling, usually used Evaporation method recovery, if the amount of lye is large, it can be recovered by three-effect evaporation, and the amount of lye is small, and it can be recovered by thin film evaporation; (3) Dye recovery. For example, Shihlin dye can be acidified into cryptobolic acid, which is in the form of colloidal particles. The liquid is recovered and reused after precipitation and filtration.
The harmless treatment can be divided into: (1) The physical treatment method includes precipitation method and adsorption method. The precipitation method mainly removes suspended solids in wastewater; the adsorption method mainly removes dissolved pollutants and decolorization in wastewater. (2) Chemical treatment methods include neutralization method, coagulation method and oxidation method. The neutralization method is to adjust the acidity and alkalinity of the wastewater, and can also reduce the chromaticity of the wastewater; the coagulation method is to remove the disperse dyes and colloidal substances in the wastewater; the oxidation method is to oxidize the reducing substances in the wastewater to precipitate the sulfur dyes and vat dyes. (3) Biological treatment methods include activated sludge, biological turntable, biological rotary drum and biological contact oxidation method.
In order to improve the quality of effluent water and meet the discharge standards or recycling requirements, several methods are often used for joint treatment.
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, 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. Appropriate treatment methods should be selected.
For example: to remove solid impurities and inorganic substances, coagulation and filtration methods can be used; to remove organic and toxic substances, chemical oxidation, biological methods and reverse osmosis methods are mainly used; decolorization can generally use coagulation and adsorption processes. In the process, ion exchange method can be used to remove heavy metals.
Chemical industry wastewater
The chemical industry wastewater mainly comes from production wastewater discharged from the petrochemical industry, coal chemical industry, acid-base industry, fertilizer industry, plastic industry, pharmaceutical industry, dye industry, and rubber industry.
The main measures for the prevention and control of chemical wastewater pollution are: first, reform the production process and equipment, reduce pollutants, prevent the discharge of wastewater, and carry out comprehensive utilization and recycling; the treatment level of wastewater that must be discharged should be selected according to the water quality and requirements. The primary treatment mainly separates suspended solids, colloids, slick oil or heavy oil in water. Methods such as water quality and quantity adjustment, natural precipitation, floating and oil separation can be used. The secondary treatment is mainly to remove the biodegradable organic dissolved matter and part of colloids, reduce the biochemical oxygen demand and part of the chemical oxygen demand in the wastewater, and usually adopt biological treatment.
A considerable amount of COD remains in the biologically treated wastewater, sometimes with high color, smell, and taste, or because of high environmental sanitation standards, it needs to be further purified by a tertiary treatment method. The tertiary treatment is mainly to remove organic pollutants and soluble inorganic pollutants that are difficult to biodegrade in wastewater. Commonly used methods are activated carbon adsorption method and ozone oxidation method, ion exchange and membrane separation technology can also be used.
Various chemical industrial wastewater can be treated with different treatment methods according to different water quality, water quantity and requirements of external drainage quality after treatment.
Acid-base wastewater
Acidic wastewater mainly comes from steel plants, chemical plants, dye plants, electroplating plants and mines, etc., which contain various harmful substances or heavy metal salts. The mass fraction of acid varies greatly, the low is less than 1%, and the high is greater than 10%. Alkaline wastewater mainly comes from printing and dyeing factories, leather factories, paper mills, oil refineries, etc. Some of them contain organic alkali or inorganic alkali.
The mass fraction of alkali is higher than 5%, and some 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.
The general principles for the treatment of acid-base wastewater are: (1) High-concentration acid-base wastewater should be recycled and reused first. According to water quality, water volume and different process requirements, plant or regional scheduling should be carried out to reuse as much as possible: if it is difficult to reuse, Or the concentration is too low and the amount of water is large. Concentration and membrane methods can be used to recover acid and alkali. (2) Low-concentration acid and alkali wastewater, such as the cleaning water of the pickling tank and the rinsing water of the alkali tank, should be neutralized. For neutralization, the principle of treating waste with waste should be considered first. For example, acid and alkali wastewater are mutually neutralized or waste alkali (slag) is used to neutralize acidic wastewater, and waste acid is used to neutralize alkaline wastewater. In the absence of these conditions, a neutralizer can be used for treatment.
Metallurgical wastewater
The main characteristics of metallurgical wastewater are large amount of water, many types, and complex water quality. Classified by 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: (1) Develop and adopt new processes and technologies that do not use or use less water and are pollution-free or less polluting, such as dry quenching, preheating of coking coal, and direct desulfurization from coke oven gas Decyanation, etc.; (2) Develop comprehensive utilization technologies, such as recovering useful substances and heat energy from waste water and waste gas, reduce material and fuel loss, (3) According to different water quality requirements, comprehensively balance, use in series, and improve water quality stabilization measures. Improve the recycling rate of water; (4) Develop new treatment processes and technologies suitable for the characteristics of metallurgical wastewater, such as the treatment of iron and steel wastewater by magnetic methods. It has the advantages of high efficiency, less land occupation, and convenient operation and management.
