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Key Treatment Technology and Typical Process Flow of High-difficulty Wastewater in 8 Major Industries
Time：
2022-09-28
Key treatment technologies and typical technological processes of difficult wastewater in 8 major industries, including pharmaceutical industry wastewater, paper industry wastewater, tanning industry wastewater, coking wastewater, electroplating wastewater, metallurgical wastewater, printing and dyeing wastewater, food processing wastewater, etc.
Pharmaceutical Industry Wastewater
1. Features
Pharmaceutical wastewater has the characteristics of large differences in composition, complex components, large amount of pollutants, high COD, low and fluctuating ratio of BOD5 and CODcr, poor biodegradability, many refractory substances, strong toxicity, intermittent discharge, water quality and pollutants. Types fluctuate and so on.
2. Composition
| Type | Source | Composition |
| Antibiotic production wastewater | Fermentation filtrate, extracted raffinate, still residue, adsorption waste and conduit waste, etc. | It mainly contains mycelium, residual nutrients, metabolites and organic solvents. The concentration of organic matter is very high, COD can reach 5000～20000mg/L, BOD can reach 2000～10000mg/L, SS concentration can reach 5000～23000mg/L, TN can reach 600～1000mg/L |
| Synthetic Drug Wastewater | In the synthesis process, the loss of raw materials, by-products, organic solvents, etc. caused by many steps and low product conversion rate | Contains a wide variety of toxic and harmful chemical substances, such as steroids, nitro compounds, aniline compounds, piperazines and fluorine, mercury, chromium copper and organic solvents ethanol, benzene, chloroform, petroleum ether and other organic compounds, metals and Pollutants such as waste acid and alkali |
| Chinese patent medicine production wastewater | Cleaning waste water, separated water, evaporation condensate water, liquid medicine loss water, etc. | Natural biological organics, such as organic acids, anthraquinones, lignin, alkaloids, tannins, tannins, proteins, carbohydrates, starches, etc. |
3. Processing technology
①Pretreatment: coagulation method, air flotation method, micro-electrolysis, Fenton reagent, catalytic oxidation, etc.;
②Anaerobic process: UASB, two-phase anaerobic digestion, EGSB, etc.;
③ Aerobic process: biological contact oxidation method, CASS, SBR, activated sludge method, etc.;
4. Typical process flow
Treatment of pharmaceutical wastewater by air flotation
Treatment of Pharmaceutical Wastewater by Membrane Separation
Combined Process for Pharmaceutical Wastewater Treatment
Paper Industry Wastewater
1. Features
Papermaking wastewater is very harmful, of which black water is the most harmful, and the pollutants it contains account for more than 90% of the total pollution discharge of the paper industry. It also consumes a large amount of dissolved oxygen in water, seriously pollutes water sources, and brings harm to the environment and human health.
The most serious environmental pollution of the middle water is the chlorine-containing wastewater generated during the bleaching process, such as chlorinated bleaching wastewater, hypochlorite bleaching wastewater, etc. In addition, bleaching waste liquor contains highly toxic carcinogen dioxin, which also poses a serious threat to the ecological environment and human health.
2. Composition
Pulp and papermaking wastewater is mainly divided into three types: black liquor, intermediate wastewater and white water.
Black liquor: cook plant fibers with alkaline agents containing NaOH or NaOH+sodium sulfate to dissolve lignin. ). Black liquor contains lignin, polypentose and total alkali, and is a high-concentration refractory wastewater.
Mid-stage wastewater: wastewater produced in the process of washing, screening and bleaching of pulp made by alkaline cooking, the COD load per ton of pulp is about 310kg. The BOD/COD is between 0.20 and 0.35, and the biodegradability is poor. The pollutants are mainly soluble COD such as lignin, cellulose, organic acids, etc. The most serious pollution is the chlorine-containing wastewater produced by bleaching.
White water: a large amount of water, mainly containing fine fibers, fillers, coatings and dissolved wood components, mainly insoluble COD, poor biodegradability, and the added preservatives are toxic.
3. Processing technology
Black liquor, middle-stage wastewater: alkali recovery, acid precipitation, LB-1 alkali precipitation, membrane separation, flocculation sedimentation, biofilm method, anaerobic biological treatment, mesh microfiltration, air flotation, advanced oxidation.
White water: filtration, flotation, sedimentation, sieving.
4. Typical process flow
Extraction of lignin from papermaking black liquor to make coal-water slurry
Shallow air flotation - oxidation pond
Coagulation air flotation - A/O process
Treatment of Alkaline Straw Pulp Wastewater by Oxidation Ditch Process
Hydrolysis and acidification - anaerobic - biological contact - coagulation and sedimentation
Air flotation treatment of paper machine white water
Tanning Industry Wastewater
1. Features
Tanning wastewater is the wastewater discharged from the tanning production process. Usually animal skins are salted or soaked in water to make them swell, limed, fleshed, dealkalized, then softened with tannin or chrome, tanned and fatliquored. Dyed to make leather. Tannery wastewater mainly comes from preparation, tanning and dyeing sections, which contain a large amount of protein, fat, inorganic salts, suspended solids, sulfides, chromium and vegetable tanning agents and other toxic and harmful substances, with high biochemical oxygen demand and high toxicity .
2. Composition
Sulfur-containing wastewater: refers to the liming wastewater and the corresponding washing process wastewater produced by the ash-alkali dehairing process in the tanning process;
Degreasing wastewater: refers to the waste liquid and the corresponding washing process wastewater formed by the use of surfactants to treat raw hide oil in the degreasing process of tanning and fur processing.
Chromium-containing wastewater: refers to the waste chrome liquid produced in the chrome tanning and chrome retanning processes and the corresponding wastewater from the washing process.
Comprehensive wastewater: refers to the collective name of various wastewaters (such as production process wastewater, factory domestic sewage, etc.) generated by tanning and fur processing enterprises or centralized processing areas and directly or indirectly discharged into comprehensive wastewater treatment projects.
3. Processing technology
single processing technology
a. Degreasing wastewater
The pollution indicators such as oil content, CODcr and BOD5 in the degreasing waste liquid are very high. Treatment methods include acid extraction, centrifugation or solvent extraction. The acid extraction method is widely used, adding H2SO4 to adjust the pH value to 3-4 for demulsification, stirring with steam and salt, and standing at 40-60 t for 2-3 hours, the oil gradually floats up to form an oil layer. The recovered oil can reach 95%, and the CODcr can be removed by more than 90%. Generally, the mass concentration of the influent oil is 8-10 g/L, and the mass concentration of the effluent oil is less than 0.1 g/L. The recovered oil is further processed and converted into mixed fatty acids, which can be used for soap making.
b, liming and dehairing wastewater
The liming and dehairing wastewater contains protein, lime, sodium sulfide, suspended solids, 28% of the total CODcr, 93% of the total S2-, and 70% of the total SS. Treatment methods include acidification, chemical precipitation and oxidation.
The acidification method is often used in production. Under negative pressure, H2SO4 is added to adjust the pH value to 4~4.5 to generate H2S gas, which is absorbed by NaOH solution to generate alkali sulfide for reuse. The soluble protein precipitated in the wastewater is filtered, washed and dried. become a product. The removal rate of sulfide can reach more than 90%, and CODcr and SS are reduced by 85% and 95%, respectively. The cost is low, the production operation is simple, the control is easy, and the production cycle is shortened.
c, chrome tanning wastewater
The main pollutant of chrome tanning wastewater is the heavy metal Ce3+, the mass concentration is about 3-4g/L, and the pH value is weakly acidic. The treatment methods include alkali precipitation and direct recycling. 90% of the domestic tanneries use the alkali precipitation method, adding lime, sodium hydroxide, magnesium oxide, etc. to the waste chromium solution, reacting and dehydrating to obtain chromium-containing sludge, which can be dissolved in sulfuric acid and then reused in the tanning section.
During the reaction, the pH value is 8.2-8.5, and the temperature is 40 °C for the best precipitation. The magnesium oxide is the best alkali precipitant, the recovery rate of chromium is 99%, and the mass concentration of chromium in the effluent is less than 1 mg/L. However, this method is suitable for large-scale tanneries, and the soluble oil, protein and other impurities in the recovery of chromium mud will affect the tanning effect.
Integrated processing technology
a. Pretreatment system: It mainly includes treatment facilities such as grille, regulating tank, sedimentation tank, and air flotation tank. The concentration of organic matter and suspended solids in the tannery wastewater is high, and the pretreatment system is used to adjust the water volume and water quality; remove SS and suspended solids; reduce part of the pollution load and create good conditions for subsequent biological treatment.
b. Biological treatment system: ρ(CODcr) of tannery wastewater is generally 3000-4000 mg/L, ρ(BOD5) is 1000-2000 mg/L, which belongs to high-concentration organic wastewater, m(BOD5)/m(CODcr) value It is 0.3-0.6, suitable for biological treatment. At present, the oxidation ditch, SBR and biological contact oxidation method are widely used in China, and the jet aeration method, batch biofilm reactor (SBBR), fluidized bed and up-flow anaerobic sludge bed ( UASB).
4. Typical process flow
Tannery Wastewater Treatment Process
Treatment process of tannery wastewater containing chromium
Coking Wastewater
1. Features
Coking wastewater is one of the main wastewater discharged from iron and steel enterprises. Coking wastewater has complex components and contains a large amount of toxic and harmful substances. It is a typical refractory organic wastewater. The removal rate of the refractory compounds in the conventional treatment method is low, so that the COD and chroma of the effluent are high and cannot meet the standard.
2. Composition
Coking wastewater is high-concentration organic wastewater produced in the process of coal coking, gas purification and coking product recovery. Coking wastewater mainly includes gas condensate in the initial cooling stage of gas, cold water at the end of gas, gas washing water and gas washing water in the gas generating station, purified benzene separation water, gas tank wastewater, coke oven water sealing water and sewage generated in other occasions.
3. Processing technology
Physical treatment method: adsorption method, coagulation and flocculation sedimentation method, Fenton reagent method
Biochemical treatment method: A/O and A2/O method, SBR method, oxidation ditch technology
Chemical treatment methods: catalytic wet oxidation technology, ozone oxidation, photocatalytic oxidation
4. Typical process flow
Coking Wastewater Treatment Process
Treatment of coking wastewater by nitrification and denitrification
Electroplating Wastewater
1. Features
The waste water produced by electroplating is highly toxic and harms the growth of soil, animals and plants. Therefore, it is necessary to strictly deal with the discharge of wastewater up to the standard, and to implement the recycling of wastewater treatment up to the standard in water-deficient areas. In terms of technical production, a certain amount of various chemicals must be added in the electroplating production process and wastewater treatment process. Electroplating wastewater can be recycled and reused after treatment. The reused water must be desalinated before it can be reused as water in the production line. The total salt content in the environment will not be reduced, and the concentrate from the resin exchange and reverse osmosis processes will still return to the ground.
2. Composition classification
According to the classification of heavy metal elements contained in heavy metal wastewater, it can generally be divided into chromium (Cr) wastewater, nickel (Ni) wastewater, cadmium (Cd) wastewater, copper (Cu) wastewater, zinc (Zn) wastewater, Gold (Au) wastewater, silver (Ag) wastewater, etc.
3. Processing technology
Air flotation method: The principle of air flotation method used to treat chrome-plating wastewater is: ferrous sulfate and hexavalent chromium undergo a redox reaction under acidic conditions, and then flocculate is formed under alkaline conditions, which are used under the action of countless fine bubbles. The flocs surfaced and the water became clear.
Ion exchange method: one of the effective means to treat electroplating wastewater and recover some metals, and it is also an important link to make some types of electroplating wastewater achieve closed-circuit circulation. However, the investment cost of the ion exchange method is very high, the system design and operation management are more complicated, and it is difficult for ordinary small and medium-sized enterprises to adapt to it, and the expected results are often not achieved due to poor maintenance and management. certain restrictions.
At present, it is more common to use ion exchange method to treat electroplating wastewater containing chromium and nickel in China, and there is relatively mature experience in design, operation and management. After treatment, the water can meet the discharge standard, and the quality of the effluent is good, and it can generally be recycled. The regenerated eluent after resin exchange adsorption saturation can be reused in the plating tank after adjusting and purifying the components of the electroplating process, basically realizing a closed-circuit circulation. In addition, the ion exchange method can also be used to treat wastewater containing copper, zinc and gold.
Electrolysis: Electrolysis treatment of electroplating wastewater is generally used in small and medium-sized factories. Its main features are that it does not need to add treatment chemicals, the process is simple, the operation is convenient, and it occupies less production space. At the same time, due to the high purity of recovered metals, it is used to recover valuable Metals have good economics. However, when the amount of water to be treated is large, the electrolysis method consumes a large amount of electricity and consumes a large amount of iron plates. At the same time, the separated sludge is as difficult to dispose of as the chemical treatment method, so it is less used.
Extraction method: The extraction method is to use a solvent that is insoluble in water but can dissolve a certain substance (called a solute or extract) in the water to be added to the wastewater, so that the solute is fully dissolved in the solvent, thereby separating and removing or recovering a certain substance from the wastewater. method of matter. The extraction operation process includes three main processes of mixing, separation and recovery.
4. Typical treatment process
Treatment of Electroplating Wastewater by Ion Exchange
Plastic electroplating wastewater treatment process
Chromium-containing wastewater treatment process
Electroplating wastewater treatment process
Electroplating wastewater treatment process
Metallurgical Wastewater
1. Features
Sewage acid wastewater is very acidic. After neutralization and removal of fluoride, the salinity of the wastewater increases, the hardness is high, and the pH value rises to 9-11. Wastewater contains zinc, copper, lead, cadmium, arsenic, nickel and other metal ions, as well as fluoride, nitrate, organic matter, colloidal particles and other pollutants. If the raw water directly enters the membrane system, the membrane will produce less water and be easily blocked. It must be softened first, and then the heavy metal ions and COD in the sewage must be removed. After the advanced membrane treatment system, the produced water can be reused.
2. Composition
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.
3. Processing technology
Treatment of pickling wastewater: A small amount of pickling wastewater can be neutralized and iron salts can be recovered; a larger amount can be recovered by freezing method, spray combustion method, diaphragm dialysis method and other methods to recover acid and iron salt or separate and recover iron oxide. If the iron oxide scale is removed by the neutral electrolysis process, there will be no pickling wastewater. However, the electrolyte must be filtered or treated by magnetic separation before it can be recycled.
Treatment of cooling water: The treatment method is to first pass through a coarse particle sedimentation tank or a hydrocyclone to remove particles with a particle size of more than 100 microns, and then send the wastewater to sedimentation to remove suspended particles; in order to improve the sedimentation effect, coagulation can be added. Agent and coagulant polyacrylamide; oil slick in water can be removed with scraper. The wastewater can be recycled after purification and cooling. The direct cooling water in the cold rolling workshop contains emulsified oil, which must first be destroyed by chemical coagulation, heating or pH adjustment to destroy the emulsified oil, and then float and separate, or directly separate by ultrafiltration. The collected waste oil can be regenerated and used as fuel.
Treatment of washing water: cyanide in wastewater can be oxidized to cyanide by chlorine, bleaching powder or ozone, etc., or ferrous sulfate can be added to make cyanide into non-toxic ferrocyanide, and tower type can also be used. Biological filter or aeration tank, etc. for biological treatment. The blast furnace gas washing water has a large amount of water, and it is very uneconomical to treat cyanide by the above method. Therefore, most of the wastewater is clarified by a sedimentation tank and then recycled.
Treatment of non-ferrous metallurgical wastewater: The treatment measures are: strengthen production management, reduce the amount of wastewater, and recover useful metals. The commonly used treatment method is the lime neutralization method, which mainly controls the pH value of the wastewater, so that the heavy metal ions become hydroxides to precipitate; After extracting the substance, harmful substances such as arsenic and fluorine can form insoluble compounds with calcium ions and precipitate and separate. In addition, ion exchange method, flotation method, reverse osmosis method, diaphragm electrolysis method, etc. can also be used to recover useful metals and purify wastewater.
4. Typical treatment process
fluidized precipitation
Coagulation/Membrane Method
Dyeing Wastewater
1. Features
Printing and dyeing wastewater is the wastewater discharged from printing and dyeing factories that process cotton, hemp, chemical fibers and their blended products. Printing and dyeing wastewater has a large amount of water, and 100-200 tons of water is consumed per ton of textile printing and dyeing, of which 80-90% becomes wastewater.
Textile printing and dyeing wastewater has the characteristics of large water volume, high content of organic pollutants, large alkalinity, and large changes in water quality, and is one of the difficult industrial wastewaters to treat. Wastewater contains dyes, pulp, additives, oils, acid and alkali, fiber impurities, sand-like substances, inorganic salts, etc.
2. Processing technology
The common treatment methods of printing and dyeing wastewater can be divided into three categories: physical method, chemical method and biological method. Physical methods mainly include grids and screens, adjustment, sedimentation, air flotation, filtration, membrane technology, etc.; chemical methods include neutralization, coagulation, electrolysis, oxidation, adsorption, disinfection, etc.; biological methods include anaerobic biological Oxygen biological method, facultative biological method.
3. Typical treatment process
Printing and dyeing wastewater treatment process
Food Processing Wastewater
1. Features
The production changes with the seasons, and the quality and quantity of wastewater also change with the seasons;
The amount of wastewater varies. The food industry ranges from small-scale domestic industries to large-scale factories. There are a wide variety of products. The raw materials, processes, and scales vary greatly. The amount of wastewater varies from a few m3/d to thousands of m3/d. ;
There are many degradable components in the food industry wastewater. For the general food industry, since the raw materials are derived from natural organic substances, the components in the wastewater are also mainly natural organic substances and do not contain toxic substances, so the biodegradability is good, and its BOD5/ COD up to 0.84;
There are many high-concentration wastewater;
The wastewater contains various microorganisms, including pathogenic microorganisms, and the wastewater is easily corrupted and smelly;
Nitrogen and phosphorus content in wastewater is high.
2. Processing technology
Physical treatment method: The physical treatment methods used for food industry sewage treatment include sieving, skimming, conditioning, sedimentation, air flotation, centrifugal separation, filtration, microfiltration, etc. The first five processes are mostly used for pretreatment or primary treatment, and the latter three are mainly used for advanced treatment.
Chemical treatment method: The chemical treatment methods for food industry sewage include neutralization, coagulation, electrolysis, redox, ion exchange, membrane separation, etc.
Biological treatment method: In food processing wastewater treatment, biological treatment process can be divided into aerobic process, anaerobic process, stabilization pond, land treatment and various combined processes formed by the combination of the above processes. Food sewage is organic sewage, and biological method is the main secondary treatment process, which aims to degrade COD and BOD5.
The aerobic biological treatment process is divided into activated sludge process and membrane process according to the growth form of the microorganisms used. The former includes traditional activated sludge method, stage aeration method, biological adsorption method, complete mixing method, delayed aeration method, oxidation ditch, batch activated sludge method (SBR), etc. The latter includes biological filters, tower biological filters, biological turntables, active biological filters, biological contact oxidation, and aerobic fluidized beds. Generally, aerobic treatment has better effect on low-concentration sewage.
The anaerobic biological treatment process is suitable for the treatment of food processing wastewater, mainly because the wastewater contains a high concentration of easily biodegradable organic matter and is non-toxic. In addition, the power consumption of anaerobic treatment is low, the generated biogas can be used as energy, and the amount of excess sludge generated is small. The anaerobic treatment system is completely closed, which is conducive to improving environmental sanitation. It can be operated seasonally or intermittently, and the sludge can be stored for a long time.
3. Typical treatment process
Treatment of food processing wastewater by CASS process
Biological treatment of food processing wastewater
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