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Industrial Wastewater Treatment Section 1

Upload time:2021-06-30

Industrial wastewater contains many toxic and harmful substances, which not only pollute the environment, but also endanger human health. Industrial wastewater treatment has always been concerned by people and social. Industrial wastewater is divided into phenol wastewater, mercury-containing wastewater, oil-containing wastewater, heavy metal wastewater, cyanide-containing wastewater, paper mill wastewater, printing and dyeing wastewater, chemical industry wastewater, metallurgical wastewater, acid-base wastewater, etc., different wastewater has different treatment methods.

Industrial waste water refers to waste water, sewage and waste liquid produced in the industrial production process, which contains industrial production materials, intermediate products and finished products that are lost with water, and pollutants generated in the production process. With the rapid development of industry, the types and quantities of waste water have increased rapidly, and the pollution of water bodies has become increasingly widespread and serious, threatening human health and safety. Therefore, for the protection of the environment, the treatment of industrial wastewater is more important than the treatment of urban sewage.

The Hazards and Treatment of Phenol-containing Wastewater

Phenol-containing wastewater mainly comes from coking plants, gas plants, petrochemical plants, insulating materials plants and other industrial sectors, 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, 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 and when the mass concentration is increased to 1mg/L, the spawning of fish will be affected, and if the phenol content is 5-10mg/L, the fish will be large death. Phenol in domestic water can affect human health. Even if the mass concentration of phenol in water is only 0.002mg/L, it will produce chlorophenol stench during disinfection with chlorine.
Usually, the phenol-containing wastewater with a mass concentration of 1000 mg/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 wastewater is recycled and phenol is concentrated and recycled for treatment. Methods of recovering phenol include solvent extraction, steam stripping, adsorption, and closed loop methods. Wastewater with a mass concentration of phenol below 300mg/L can be treated by biological oxidation, chemical oxidation, physical and chemical oxidation and other methods before being discharged or recycled.

The characteristics and Treatment of Mercury-containing Compounds 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 to remove 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 method or sulfide precipitation method. Acidic mercury-containing wastewater can be treated by metal reduction. Low-concentration mercury-containing wastewater can be treated by activated charcoal adsorption, chemical coagulation or activated sludge method. Organic mercury wastewater is more difficult to treat. Generally, organic mercury is oxidized to inorganic mercury and then treated.
What are the characteristics of oily wastewater and how to treat it?
Oily wastewater mainly comes from industrial sectors such as petroleum, petrochemical, iron and steel, coking, gas generating stations, and mechanical processing. The oil pollutants in the wastewater have a relative density of less than 1, except for the relative density of heavy tar which is above 1.1.
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, suspended in water. (3) Emulsified oil, the particle size of the oil droplets is less than 10μm, and it is not easy to separate from the wastewater. Because the oil concentration in wastewater discharged from different industrial sectors is very different, such as wastewater generated in the oil refining process, the oil content is about 150-1000 mg/L, the tar content in the coking wastewater is about 500-800 mg/L, and the waste water 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 slick 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 more difficult. Therefore, the emulsification phenomenon should be prevented or reduced. One of the methods is to reduce the emulsification of the 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, so as not to increase the degree of emulsification. The treatment method usually adopts air flotation method and demulsification method.
What are the sources of heavy metal wastewater and its treatment principles?
Heavy metal wastewater mainly comes from wastewater discharged from mining, smelting, electrolysis, electroplating, pesticides, medicine, paint, pigments and other enterprises. 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 ions 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 resins. After regeneration, it is transferred from the ion exchange resin to the regeneration waste liquid. Therefore, the principles of heavy metal wastewater treatment are: first, the most fundamental is to reform the production process, avoid or use less toxic heavy metals, and secondly, use reasonable process, scientific management and operation to reduce the amount of heavy metals and the amount of waste water lost. Minimize 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 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.
How to treat cyanide-containing 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. It 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 the human body is 0.18, potassium cyanide is 0.12g, and the mass concentration of cyanide to fish in the 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 from the outside. If the non-cyanide electroplating method is adopted, the industrial wastewater of the electroplating workshop can be eliminated. (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 and so on. 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, so it is rarely used.
What are the characteristics of pesticide wastewater and its treatment methods?
There are many varieties of pesticides, and the quality of pesticide wastewater is complex. Its main characteristics are (1) high concentration of pollutants, chemical oxygen demand (COD) can reach tens of thousands of mg per liter; (2) high toxicity, in addition to pesticides and intermediates in wastewater In vitro, it also contains toxic substances such as phenol, arsenic and mercury, as well as many difficult-to-degrade substances: (3) It has a foul smell and is irritating to the human respiratory tract and mucous membranes; (4) Water quality and volume 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 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 residues is the direction of pesticide development. Some countries have banned the production of organic chlorine and organic mercury pesticides such as BHC and actively researched and used microbial pesticides. This is a new way to fundamentally prevent pesticide wastewater from polluting the environment.


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