Industrial wastewater refers to the wastewater, sewage, and waste liquid generated during the industrial production process, which contains industrial production materials, intermediate products, and products that are lost with water, as well as pollutants generated during the production process. Common types of industrial wastewater and their characteristics include:
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 adopt the flue gas limestone gypsum wet desulfurization process. This process mainly consists of a limestone slurry preparation system, a gypsum dewatering system, and a desulfurization wastewater treatment system. The water in the slurry of the desulfurization device will accumulate heavy metal elements and Cl - during continuous circulation, which will accelerate the corrosion of the desulfurization equipment and affect the quality of gypsum. Therefore, it is necessary to discharge the wastewater in a timely manner.
Power plant desulfurization wastewater treatment process
Process flow of desulfurization wastewater treatment in power plants: desulfurization wastewater → wastewater tank → wastewater pump → pH neutralization tank → settling tank → flocculation tank → clarifier → outlet tank → outlet pump → standard discharge
&bsp; The desulfurization wastewater treatment system includes three parts: wastewater treatment, dosing, and sludge treatment. The wastewater treatment system mainly consists of equipment such as wastewater tank, triple tank, clarification tank, sludge pump, outlet tank, clean water pump, fan, dewatering machine, etc. 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, etc. To meet the wastewater discharge standards, corresponding wastewater treatment devices need to be equipped.
2. Chemical industry wastewater
Chemical industry wastewater mainly comes from production wastewater discharged from industries such as petrochemicals, coal chemistry, acid alkali, fertilizer, plastics, pharmaceuticals, dyes, rubber, etc.
The main measures for preventing and controlling chemical wastewater pollution are: firstly, reforming production processes and equipment, reducing pollutants, preventing wastewater discharge, and conducting comprehensive utilization and recycling; The treatment level of wastewater that must be discharged should be selected according to water quality and requirements.
The primary treatment mainly separates suspended solids, colloids, floating oil or heavy oil in water. Water quality and quantity regulation, natural sedimentation, flotation, and oil separation methods can be used.
Secondary treatment mainly involves removing biodegradable organic solutes and some colloids, reducing the biochemical oxygen demand and some chemical oxygen demand in wastewater, and usually using biological methods for treatment. After biological treatment, there is still a considerable amount of COD remaining in the wastewater, sometimes with high color, odor, and taste, or due to high environmental hygiene standards, a three-level treatment method needs to be used for further purification.
The third level treatment mainly removes organic pollutants and dissolved inorganic pollutants that are difficult to biodegrade from wastewater. Common methods include activated carbon adsorption and ozone oxidation, as well as ion exchange and membrane separation techniques. Various chemical industry wastewater can be treated using different methods based on the requirements of water quality, quantity, and the quality of the discharged water after treatment.
3、 Printing and dyeing industry wastewater
The printing and dyeing industry consumes a large amount of water, usually 100-200 tons per ton of textile processed. 80% -90% of it is discharged as printing and dyeing wastewater. Common governance methods include recycling and harmless treatment.
Recycling:
Wastewater can be recycled and reused according to its water quality characteristics, such as the separation of bleaching and refining wastewater and dyeing and printing wastewater. The former can be washed by convection Multi use of water to reduce emissions;
Alkali recovery and utilization usually use evaporation method. If the amount of alkali is large, three effect evaporation can be used for recovery. If the amount of alkali is small, thin film evaporation can be used for recovery;
Dye recycling Shilin dye can be acidified to form aspartic acid, which appears as colloidal particles Suspended in the residual liquid, recovered and utilized after precipitation and filtration.
Harmless treatment:
There are physical processing methods such as precipitation and adsorption. The sedimentation method mainly removes suspended solids in wastewater; The adsorption method is mainly used to remove dissolved pollutants and decolorize wastewater.
Chemical treatment methods include neutralization, coagulation, and oxidation. The neutralization method is used to regulate the acidity and alkalinity of wastewater, and can also reduce the color of wastewater; The coagulation method is used to remove dispersed dyes and colloidal substances from wastewater; The oxidation method involves oxidizing reducing substances in wastewater to precipitate sulfide dyes and reducing dyes.
Biological treatment methods include activated sludge, biological turntable, biological drum, and biological contact oxidation method. In order to improve the effluent quality and meet discharge standards or recycling requirements Often, several methods need to be used in conjunction for processing.
4. Paper industry wastewater
Papermaking wastewater mainly comes from the two production processes of pulp and papermaking in the paper industry. Pulping is the process of separating fibers from plant materials, making pulp, and then bleaching it; Papermaking is the process of diluting, shaping, pressing, and drying pulp to produce paper. Both processes discharge a large amount of wastewater.
The wastewater generated from pulp production is the most severely polluted. The wastewater discharged during pulp washing is black brown in color, known as black water. Black water has a high concentration of pollutants, with a BOD of 5-40g/L, and contains a large amount of fibers, inorganic salts, and pigments. The wastewater discharged from the bleaching process also contains a large amount of acidic and alkaline substances. The wastewater discharged from the paper machine is called white water, which contains a large amount of fibers and fillers and adhesives added during the production process.
The treatment of wastewater in the paper industry should focus on improving the recycling rate, reducing water consumption and wastewater discharge, while actively exploring various reliable, economical, and effective treatment methods that can fully utilize the useful resources in the wastewater. For example, flotation can recover fibrous solid substances from white water with a recovery rate of up to 95%, and clarified water can be reused; The combustion method can recover sodium hydroxide, sodium sulfide, sodium sulfate, and other sodium salts combined with organic compounds from black water.
Neutralization method to adjust the pH value of wastewater; Coagulation precipitation or flotation methods can remove suspended solids from wastewater; Chemical precipitation method can decolorize; Biological treatment can remove BOD and is more effective for kraft paper wastewater; The wet oxidation method has been successful in treating sulfite pulp wastewater. In addition, there are also treatment methods such as reverse osmosis, ultrafiltration, and electrodialysis used both domestically and internationally.
5、 Dye production wastewater
Dye production wastewater contains acids, bases, salts, halogens, hydrocarbons, amines, nitro compounds, dyes and their intermediates, and some also contain pyridine, cyanide, phenol, benzidine, as well as heavy metals such as mercury, cadmium, chromium, etc. These wastewater components are complex Toxic and difficult to handle. Therefore, the treatment of dye production wastewater It should be based on the characteristics of wastewater and the requirements for its discharge Choose appropriate processing methods.
For example, to remove solid impurities and inorganic substances, coagulation and filtration methods can be used; The main methods for removing organic and toxic substances include chemical oxidation, biological methods, and reverse osmosis; Decolorization can generally be achieved through a process consisting of coagulation and adsorption, while removal of heavy metals can be achieved through methods such as ion exchange.
6、 Food industry wastewater
The food industry has a wide range of raw materials and a wide variety of products, resulting in significant differences in the amount and quality of wastewater discharged.
The main pollutants in wastewater are:
Solid substances floating in wastewater, such as vegetable leaves, fruit peels, minced meat, poultry feathers, etc; Substances suspended in wastewater include oil, protein, starch, colloidal substances, etc; Dissolved acids, bases, salts, sugars, etc. in wastewater; Mud, sand, and other organic matter carried by raw materials; Pathogenic bacteria and toxins, etc.
The characteristics of food industry wastewater are high organic matter and suspended solids content, easy to decompose, and generally not highly toxic. Its harm mainly lies in eutrophication of water bodies, leading to the death of aquatic animals and fish, causing organic matter deposited at the bottom of the water to produce odors, deteriorating water quality, and polluting the environment.
In addition to appropriate pretreatment based on water quality characteristics, biological treatment is generally recommended for the treatment of wastewater in the food industry. If high effluent quality is required or due to high organic content in wastewater, two-stage aeration tanks or two-stage biological filters, or multi-stage biological turntables can be used Alternatively, two biological treatment devices can be used in combination, or anaerobic aerobic series can be employed.
7. Pesticide wastewater
There are many types of pesticides, and the quality of pesticide wastewater is complex. Its main features are:
The concentration of pollutants is high, with a chemical oxygen demand (COD) of tens of thousands of mg per liter. The wastewater is highly toxic, containing not only pesticides and intermediates, but also toxic substances such as phenol, arsenic, mercury, and many substances that are difficult for organisms to degrade; It has a foul odor and is irritating to the respiratory tract and mucous membranes of humans; The water quality and quantity are unstable.
Therefore, pesticide wastewater causes serious environmental pollution. The purpose of pesticide wastewater treatment is to reduce the concentration of pollutants in pesticide production wastewater, improve the recycling rate, and strive for harmless treatment. The treatment methods for pesticide wastewater include activated carbon adsorption, wet oxidation, solvent extraction, distillation, and activated sludge process.
However, developing efficient, low toxicity, and low residue new pesticides is the direction of pesticide development. Some countries have banned the production of organochlorine and organic mercury pesticides such as hexachlorocyclohexane, 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 sectors such as electroplating, coal gas, coking, metallurgy, metal processing, chemical fiber, plastics, pesticides, and chemical industry.
Cyanide containing wastewater is a highly toxic industrial wastewater that is unstable in water and easy to decompose. Both inorganic cyanide and organic cyanide are highly toxic substances that 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 mass concentration of cyanide to fish in water is 0.04~0.1mg/L.
The main measures for treating cyanide containing wastewater include:
Reforming the process to reduce or eliminate the discharge of cyanide containing wastewater, such as using cyanide free electroplating method to eliminate industrial wastewater in electroplating workshops.
Wastewater with high cyanide content should be recycled, while wastewater with low cyanide content should be purified before discharge. The recycling methods include acidification aeration alkali absorption method, steam desorption method, etc.
The treatment methods include alkaline chlorination, electrolytic oxidation, pressure hydrolysis, biochemical method, biological iron method, ferrous sulfate method, air stripping method, etc. The alkaline chlorination method is widely used, while the ferrous sulfate method is not thorough and stable. The air stripping method not only pollutes the atmosphere, but also fails to meet the discharge standards for effluent. Less commonly used.
9、 Phenol containing wastewater
Phenol containing wastewater mainly comes from industrial sectors such as coking plants, gas plants, petrochemical plants, insulation material plants, as well as petroleum cracking to produce ethylene, synthetic phenol, polyamide fibers, synthetic dyes, organic pesticides, and phenolic resin production processes. Phenolic wastewater mainly contains phenolic compounds, which are a type of protoplasm toxin that can cause protein coagulation.
10. Mercury containing wastewater
Mercury containing wastewater mainly comes from non-ferrous metal smelters, chemical plants, pesticide factories, paper mills, dye factories, and thermal instrument factories. The toxicity of various mercury compounds varies greatly, such as methylmercury. Methylmercury is easily absorbed into the human body, not easily degraded, excreted slowly, and easily accumulates in the brain.
11. Heavy metal wastewater
Heavy metal wastewater mainly comes from wastewater discharged by mining, smelting, electrolysis, electroplating, pesticide, pharmaceutical, paint, pigment and other enterprises. The types, contents, and forms of heavy metals in wastewater vary among different production enterprises.
The principle of treating heavy metal wastewater is:
The most fundamental is to reform the production process and avoid or reduce the use of highly toxic heavy metals; Secondly, reasonable process flow, scientific management and operation should be adopted to reduce the amount of heavy metals used and the loss with wastewater flow, and minimize the amount of discharged wastewater as much as possible. Heavy metal wastewater should be treated on-site at the production site and mixed with other wastewater to avoid complicating the treatment process. It should not be directly discharged into urban sewers without treatment to avoid expanding heavy metal pollution.
The treatment of heavy metal wastewater can usually be divided into two categories:
One is to transform dissolved heavy metals in wastewater into insoluble metal compounds or elements, which are removed from the wastewater through precipitation and flotation. Applicable methods include neutralization precipitation, sulfide precipitation, flotation separation, electrolytic precipitation (or flotation), membrane electrolysis, etc;
The second method is to concentrate and separate heavy metals in wastewater without changing their chemical form. Applicable methods include reverse osmosis, electrodialysis, evaporation, and ion exchange. These methods should be used separately or in combination according to the quality and quantity of wastewater.
12. The main characteristics of metallurgical wastewater are large water volume, diverse types, and complex and variable water quality. According to the sources and characteristics of wastewater, it mainly includes cooling water, acid washing wastewater, washing wastewater (dust removal, gas or flue gas), slag flushing wastewater, coking wastewater, and wastewater from condensation, separation or overflow in production.
The development trend of metallurgical wastewater treatment is:
Develop and adopt new processes and technologies that do not require or use less water, and are pollution-free or have less pollution, such as dry quenching of coke, preheating of coking coal, and direct desulfurization and decyanation of coke oven gas; Developing comprehensive utilization technologies, such as recovering useful substances and heat energy from wastewater and exhaust gases, to reduce material and fuel loss; According to different water quality requirements, comprehensively balance and use in series, while improving water quality stability measures, continuously increasing the water recycling rate;
Develop new treatment processes and technologies suitable for the characteristics of metallurgical wastewater, such as using magnetic methods to treat steel wastewater It has the advantages of high efficiency, small footprint, and convenient operation and management.
13、 Acid alkali wastewater
Acidic wastewater mainly comes from steel plants, chemical plants, dye plants, electroplating plants, and mines, which contain various harmful substances or heavy metal salts. The quality fraction of acid varies greatly, ranging from less than 1% to over 10%.
Alkaline wastewater mainly comes from printing and dyeing factories, leather factories, paper mills, oil refineries, etc. Some of them contain organic bases or inorganic bases. The mass fraction of alkali is sometimes higher than 5% and sometimes lower than 1%. Acid alkali wastewater often contains acid salts, basic salts, and other inorganic and organic substances in addition to acid and alkali.
Acid alkali wastewater has strong corrosiveness and needs to be properly treated before being discharged.
The general principles for treating acid-base wastewater are:
High concentration acid-base wastewater should be prioritized for recycling and reuse. Based on water quality, quantity, and different process requirements, plant or regional scheduling should be carried out to maximize reuse. If reuse is difficult or the concentration is low and the water volume is large, concentrated methods can be used to recover acid-base.
Low concentration acid-base wastewater, such as cleaning water for acid pickling tanks and rinsing water for alkaline washing tanks, should be neutralized.
For neutralization treatment, the principle of treating waste with waste should be considered first. Neutralize acidic and alkaline wastewater with each other or use waste alkali (slag) to neutralize acidic wastewater, and use waste acid to neutralize alkaline wastewater. When these conditions are not met, neutralizing agents can be used for treatment.
14、 Mineral processing wastewater
Mineral processing wastewater has the characteristics of large water volume, high suspended solids content, and a variety of harmful substances. Its harmful substances are heavy metal ions and mineral processing agents. Heavy metal ions include copper, zinc, lead, nickel, barium, cadmium, as well as arsenic and rare elements.
There are several types of flotation agents added during the beneficiation process, including capture agents Such as yellow medicine (RocssMe), black medicine [(RO) 2PSSMe], white medicine [CS (NHC6H5) 2]; Suppression penalties, such as cyanide salts (KCN, NaCN) and sodium silicate (Na2SiO3); Foaming agents such as turpentine and cresol (C6H4CH30H); Active penalties, such as copper sulfate (CuS04) and heavy metal salts; Sulfurizing agents, such as sodium sulfide; Mineral slurry regulators, such as sulfuric acid, lime, etc.
Mineral processing wastewater can be effectively removed from suspended solids in the wastewater through tailings dams, and the content of heavy metals and flotation agents can also be reduced. If the emission requirements cannot be met, further treatment should be carried out. Common treatment methods include:
The removal of heavy metals can be achieved through lime neutralization and calcination of dolomite adsorption methods; The main flotation reagents can be obtained by ore adsorption method and activated carbon adsorption method; Cyanide containing wastewater can be treated by chemical oxidation method.
15. Oily wastewater
Oily wastewater mainly comes from industrial sectors such as petroleum, petrochemicals, steel, coking, gas generation stations, and mechanical processing. Oil pollutants in wastewater have a relative density of less than 1, except for heavy tar which has a relative density of 1.1 or higher. Oil substances usually exist in three states in wastewater.
Floating oil with droplet size greater than 100 μ m, easy to separate from wastewater. Disperse oil The oil droplet size ranges from 10 to 100 μ m and floats in water. Emulsified oil, with droplet size less than 10 μ m, is difficult to separate from wastewater.
Due to the significant differences in oil concentration in wastewater discharged from different industrial sectors, such as wastewater generated during oil refining with an oil content of about 150-1000mg/L, coking wastewater with a tar content of about 500-800mg/L, and wastewater discharged from gas generation stations with a tar content of up to 2000-3000mg/L.
Therefore, the treatment of oily wastewater should first use oil separators to recover floating oil or heavy oil, with a treatment efficiency of 60% to 80%, and an oil content of about 100-200mg/L in the effluent; Emulsified oil and dispersed oil in wastewater are difficult to treat, so emulsification should be prevented or reduced.
One method is to pay attention to reducing the emulsification of oil in wastewater during the production process; Secondly, during the treatment process, try to minimize the number of times a pump is used to lift the wastewater, in order to avoid increasing the degree of emulsification. The processing methods usually include air flotation and emulsion breaking.
