Industrial wastewater refers to wastewater, sewage and waste liquid produced in industrial production processes, which contain industrial production materials, intermediate products and products that are lost with water, and pollutants produced during the production process, summarizing chemical industrial wastewater, printing and dyeing industrial wastewater. 15 kinds of industrial wastewater treatment processes such as paper industry wastewater, dye production wastewater, food industry wastewater and pesticide wastewater.

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

Characteristics of desulfurization wastewater from power plants:

Most desulfurization devices in power plants use flue gas limestone-gypsum wet desulfurization process. The process mainly consists 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, the corrosion of the desulfurization equipment is accelerated, and on the other hand, the quality of the gypsum is affected, and the wastewater needs to be discharged in time.

Power plant desulfurization wastewater treatment process

Power plant desulfurization wastewater treatment process: desulfurization wastewater → waste water tank → wastewater pump → pH neutralization tank → settling tank → flocculation tank → clarifier → water tank → water pump → discharge standard
The desulfurization wastewater treatment system includes three parts: wastewater treatment, dosing and sludge treatment. The wastewater treatment system is mainly composed of waste water tank, triple tank, clarification tank, mud pump, water outlet tank, clean water pump, fan and dewatering machine. In addition to a large amount of Cl-, Mg2+, the impurities in the desulfurization wastewater 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, a corresponding wastewater treatment device is required.

2. Chemical industry wastewater

The chemical industry wastewater mainly comes from the production wastewater discharged from the petrochemical industry, the coal chemical industry, the acid and alkali industry, the fertilizer industry, the plastics industry, the pharmaceutical industry, the dye industry, and the 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 wastewater discharge, comprehensive utilization and recycling;

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

The secondary treatment mainly removes the biodegradable organic solute and some colloids, reduces the biochemical oxygen demand and part of the chemical oxygen demand in the wastewater, and is usually treated by biological methods. A considerable amount of COD remains in the biologically treated wastewater, sometimes with a high color, smell, taste, or high environmental sanitation standards, and further purification is required by a three-stage treatment.

The tertiary treatment is mainly to remove organic pollutants and dissolved inorganic pollutants that are difficult to biodegrade in wastewater. Commonly used methods include activated carbon adsorption and ozone oxidation, and ion exchange and membrane separation techniques can also be used. Various chemical industry wastewaters can be selected according to different water quality, water quantity and post-treatment external drainage quality.

3. Printing and dyeing industrial wastewater

The printing and dyeing industry uses a large amount of water, and usually consumes 100 to 200 tons of water per 1 t of textiles. 80%~90% of them are discharged by printing and dyeing wastewater. Commonly used treatment methods are recycling and harmless treatment.

Recycle and re-use:

Waste water can be recycled separately according to the characteristics of water quality, such as the separation of bleaching and smelting wastewater and dyeing printing wastewater. The former can be used for convection washing. One water is used to reduce emissions;

The recovery and utilization of lye is usually carried out by evaporation method. If the amount of lye is large, it can be recovered by three-effect evaporation. The amount of lye is small, and it can be recovered by evaporation of the film;

Dye recovery, such as Shilin dye can be acidified into cryptic acid, as colloidal particles. Suspended in the residual liquid, filtered by precipitation and recycled.

Harmless treatment can be divided into:

The physical treatment methods include a precipitation method and an adsorption method. The precipitation method mainly removes suspended matter in the wastewater; the adsorption method mainly removes dissolved pollutants and discoloration in the wastewater.

The chemical treatment methods include a neutralization method, a coagulation method, and an oxidation method. The neutralization method is to adjust the pH in the wastewater, and also to reduce the color 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 the vat dyes.

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

4. Paper industry wastewater

The papermaking wastewater mainly comes from the two production processes of pulping and papermaking in the paper industry. Pulping is to separate the fibers in the plant material, make a slurry, and then bleach; papermaking is to dilute, shape, press, and dry the slurry to make paper. Both processes discharge large amounts of wastewater.
The wastewater produced by pulping is the most polluted. The waste water discharged during 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, which contains a lot of fiber, inorganic salt and pigment. 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, called white water, contains a large amount of fibers and fillers and rubbers added during the production process.

The treatment of paper industry wastewater should focus on increasing the recycling rate, reducing water consumption and wastewater discharge, and actively exploring various reliable, economical and adequate treatment methods for utilizing useful resources in wastewater. For example, the flotation method can recover fibrous solid materials 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 substances in black water.

The neutralization method adjusts the pH value of the wastewater; the coagulation sedimentation or flotation method can remove the suspended solids in the wastewater; the chemical precipitation method can decolorize; the biological treatment method can remove the BOD, and is effective for the kraft paper wastewater; the wet oxidation treatment of the sulfite pulp wastewater success. In addition, reverse osmosis, ultrafiltration, electrodialysis and other treatment methods are also used at home and abroad.

5. Dye production wastewater

Dye production wastewater contains acids, bases, salts, halogens, hydrocarbons, amines, nitros and dyes and their intermediates, and some also contain pyridine, cyanide, phenol, benzidine and heavy metals such as mercury, cadmium, chromium and so on. These wastewater components are complex, 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. Choose the appropriate treatment.
For example, the removal of solid impurities and inorganic substances, coagulation method and filtration method can be used; the removal of organic matter and toxic substances mainly adopts chemical oxidation method, biological method and reverse osmosis method; decolorization can generally adopt a process composed of coagulation method and adsorption method. In the process, the heavy metal can be removed by ion exchange or the like.

6. Food industry wastewater

The food industry has a wide range of raw materials and a wide variety of products. The amount of water and water quality discharged from wastewater are very different.
The main pollutants in the wastewater are: solid materials floating in the wastewater, such as vegetable leaves, peels, minced meat, bird feathers, etc.; substances suspended in the wastewater are oils, proteins, starches, colloids, etc.; acids dissolved in the wastewater , alkali, salt, sugar, etc.; mud and other organic matter entrained in raw materials; pathogenic bacteria and so on.

The waste water of the food industry is characterized by high content of organic substances and suspended solids, easy to be spoiled, and generally no major toxicity. The hazard is mainly to make the water body eutrophication, causing the death of aquatic animals and fish, causing the organic matter deposited on the bottom to produce odor, deteriorating water quality and polluting the environment.

In addition to proper pretreatment according to the characteristics of water quality, wastewater treatment in food industry should generally adopt biological treatment. If the effluent water quality is very high or because the organic matter 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 can be used. – Aerobic series.

7. Pesticide wastewater

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

The concentration of pollutants is high, and the chemical oxygen demand (COD) can reach tens of thousands of milligrams per liter. It is highly toxic. In addition to pesticides and intermediates, wastewater contains toxic substances such as phenol, arsenic and mercury, as well as many substances that are difficult to degrade. It has a foul smell and is irritating to the human respiratory tract and mucous membranes; water quality and water 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 the wastewater of pesticide production, improve the recycling rate, and strive to achieve harmlessness. The treatment methods of the pesticide wastewater 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. Some countries have banned the production of organochlorine and organic mercury pesticides such as 666, and actively researched and used microbial pesticides. This 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, plastics, pesticides, and chemical industries.

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

The main treatment measures for cyanide-containing wastewater are:

Reform the process to reduce or eliminate the effluent containing cyanide. If the cyanide-free plating method is used, the industrial wastewater in the electroplating workshop can be eliminated.

Waste water with high cyanide content should be recycled, and waste water with low cyanide content should be purified before being discharged. The recovery methods include acidification aeration-alkali absorption method, steam desorption method, and the like.

The treatment methods include alkaline chlorination method, electrolytic oxidation method, pressurized hydrolysis method, biochemical method, bio-iron method, ferrous sulfate method, air stripping method, and the like. Among them, the alkaline chlorination method is widely used, the ferrous sulfate method is not thorough and unstable, and the air blowing method not only pollutes the atmosphere, but also fails to meet the discharge standard. Less used.

9. Phenol wastewater

The phenol-containing wastewater mainly comes from the industrial sectors such as coking plants, gas plants, petrochemical plants, and insulating materials plants, as well as the production process of petroleum cracking to ethylene, synthetic phenol, polyamide fiber, synthetic dyes, organic pesticides and phenolic resins. The phenol-containing wastewater mainly contains a phenol-based compound, which is a protoplasmic poison that can coagulate the protein.

10. Mercury-containing wastewater

Mercury-containing wastewater mainly comes from non-ferrous metal smelters, chemical plants, pesticide plants, paper mills, dye factories and thermal instrumentation plants. The toxicity of various mercury compounds varies greatly. For example, methylmercury, methylmercury is easily absorbed into the human body, is not easily degraded, and excretion is slow and easily accumulates in the brain.

11. Heavy metal wastewater

Heavy metal wastewater mainly comes from wastewater discharged from mines, smelting, electrolysis, electroplating, pesticides, medicine, paints, pigments and other enterprises. The type, content and form of heavy metals in wastewater vary with different production companies.

The principle of heavy metal wastewater treatment is:

The most fundamental is to reform the production process, no need to use less heavy metals; secondly, use reasonable process, scientific management and operation, reduce the amount of heavy metals and the amount of waste water, and minimize the amount of wastewater discharged. Heavy metal wastewater should be treated in situ at the place of production, and different other wastewaters should be mixed to avoid complicating the treatment. It should not be discharged directly into urban sewers without treatment, so as to avoid the expansion of heavy metal pollution.

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

The first is to convert the heavy metal in the dissolved state into an insoluble metal compound or element, which is 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 the heavy metals in the wastewater without changing the chemical form. The applicable methods include reverse osmosis, electrodialysis, evaporation and ion exchange. These methods should be used singly or in combination depending on the quality of the wastewater, the amount of water, and the like.

12. Metallurgical wastewater

The main features of metallurgical wastewater are large water volume, various types, and complex and variable water quality. Classified according to the source and characteristics of wastewater, there are mainly cooling water, pickling wastewater, washing wastewater (dust removal, gas or flue gas), slag wastewater, coking wastewater, and wastewater that is condensed, separated or overflowed from production.

The trend of metallurgical wastewater treatment development is:

Develop and adopt new technologies and technologies that use no or little water and no pollution or less pollution, such as dry quenching, coking coal preheating, direct desulfurization and denitrification from coke oven gas, etc.; Recycling useful materials and heat energy in waste water and waste, reducing material fuel loss; comprehensively balancing and streamlined use according to different water quality requirements, improving water quality stabilization measures, continuously improving water recycling rate; developing new treatment process suitable for metallurgical wastewater characteristics And technology, such as the use of magnetic treatment of steel wastewater. It has the advantages of high efficiency, small footprint, convenient operation and management.

13. Acid and alkali wastewater

Acidic wastewater mainly comes from steel plants, chemical plants, dye factories, electroplating plants and mines, which contain various harmful substances or heavy metal salts. The acid mass fraction varies widely, from less than 1% at low and greater than 10% at high.

Alkaline wastewater mainly comes from printing and dyeing factories, leather factories, paper mills, oil refineries and so on. Some of them contain organic bases or inorganic bases. The mass fraction of the base is higher than 5%, and some are less 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 principle of treating acid and alkali wastewater is:

High-concentration acid-base wastewater should be recycled in priority. According to water quality, water quantity and different process requirements, plant or regional scheduling should be carried out as much as possible. If it is difficult to reuse, or the concentration is low, the water volume is large. The method of recovering acid and alkali.

Low-concentration acid-base wastewater, such as washing water in the acid washing tank and rinsing water in the alkali washing tank, should be neutralized.

For neutralization treatment, the principle of waste treatment should be considered first. For example, acid or alkali wastewater neutralizes each other or neutralizes acidic wastewater with waste alkali (slag), and neutralizes alkaline wastewater with waste acid. In the absence of these conditions, a neutralizing agent treatment can be employed.

14. Mineral processing wastewater

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

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

The ore dressing wastewater can effectively remove suspended solids from the wastewater through the tailings dam, and the content of heavy metals and flotation reagents can also be reduced. If the emission requirements are not met, further treatment should be carried out. Commonly used treatment methods include lime neutralization method and roasting dolomite adsorption method for heavy metals removal; ore adsorption method and activated carbon adsorption method for main flotation reagents; The cyanide wastewater can be chemically oxidized.

15. Oily wastewater

Oily wastewater mainly comes from petroleum, petrochemical, steel, coking, gas generating stations, mechanical processing and other industrial sectors. The oil-contaminated substances in the wastewater have a relative density of less than 1 except for the relative density of heavy tar of 1.1 or more. Oils are usually present in three states in wastewater.

Floating oil, oil droplets larger than 100μm, easy to separate from the wastewater.

Disperse the oil, the oil droplets have a particle size between 10 and 100 μm, and float in water.

Emulsified oil, oil droplet size less than 10μm, difficult to separate from wastewater.

Because the oil concentration in the wastewater discharged by different industrial sectors varies greatly, such as wastewater generated during the refining process, the oil content is about 150~1000mg/L, the tar content in the coking wastewater is about 500~800mg/L, and the gas is discharged from the gas station. The tar content can reach 2000~3000mg/L.

Therefore, the treatment of oily wastewater should first use the grease trap to recover the oil or heavy oil. The treatment efficiency is 60%~80%, and the oil content in the effluent is about 100~200mg/L. The emulsified oil and dispersed oil in the wastewater are difficult. Treatment should prevent or mitigate emulsification.

First, pay attention to reduce the emulsification of oil in wastewater during the production process;

Second, in the process of treatment, minimize the number of times the pump is used to lift the wastewater, so as not to increase the degree of emulsification. The treatment method usually uses air flotation and demulsification.