Dry stuff! The sources and treatment methods of 21 common pollutants in sewage treatment!

1. Oxygen-consuming organic matter (easily biochemical)

The oxygen-consuming organic matter (easy to biochemical) in sewage mainly includes humic acid, protein, esters, Compounds such as sugars and amino acids exist in wastewater in a suspended or dissolved state. Under the action of microorganisms, these organic substances can be decomposed into simple inorganic substances such as CO2. However, because decomposition in natural water bodies requires the consumption of dissolved oxygen in the water, they are called oxygen-consuming organic substances.

Once sewage containing these substances enters the water body, it will reduce the dissolved oxygen content and cause the water body to turn black and smelly. Domestic sewage and industrial wastewater discharged by food, paper, petrochemical, chemical fiber, pharmaceutical, printing and dyeing and other enterprises contain large amounts of oxygen-consuming organic matter.

According to statistics, the oxygen-consuming organic matter discharged by my country's paper industry accounts for about 1/4 of the total industrial wastewater discharge. The concentration of organic matter in urban sewage is not high, but due to the large amount of water, urban sewage The total amount of oxygen-consuming organic matter emitted is also large. The key problem to be solved in secondary biological treatment of sewage is to remove most of these substances from sewage.

The composition of oxygen-consuming organic matter is complex and it is very difficult to measure the concentration of various gum organic matter. In actual work, cODCr, BOD5, TOC, TOD and other indicators are commonly used to express it. Generally speaking, the higher the above index value, the more dissolved oxygen is consumed in the water and the worse the water quality is. When the BOD5 in natural water bodies is lower than 3 mg/L, when the water quality is good and reaches 7.5 mg/L, the water quality is already poor and exceeds 10 mg/L, indicating that the water quality is already very poor and the dissolved oxygen in it is close to zero.

Easily degradable organic matter can be removed by biochemical methods, including push-flow activated sludge method (such as aeration tank), sequential batch activated sludge method (such as SBR, CASS process) , biofilm or MBR, etc.

2. Refractory organic matter

Refractory organic matter refers to organic matter that cannot be degraded by undomesticated activated sludge, and after a certain period of time Organic compounds that degrade to some extent after domestication. Some toxic macromolecules in wastewater (polycyclic and other long-chain organic compounds represented by organochlorides, organophosphorus pesticides, organic heavy metal compounds, aromatics) are organic substances that are difficult to be degraded by microorganisms, and some cannot be degraded by microorganisms at all. Microbial degradation can be called inert organic matter.

Wastewater containing such organic matter should be treated separately by cultivating special microorganisms, or treated with anaerobic and other special processes to convert part of the CODCr into BOD5, improve biodegradability, and then mix with other wastewater. Perform secondary biological treatment.

　3. Organic nitrogen and ammonia nitrogen

　Organic nitrogen mainly exists in the form of protein, as well as urea, muramic acid, fatty amines, uric acid and organic nitrogen. Alkali and other amino-containing and non-amino compounds, some organic nitrogen such as pectin, chitin and quaternary ammonium compounds are difficult to biodegrade. Wastewater discharged from industries that produce or use these organic nitrogens as raw materials will contain these organic nitrogens.

Industries such as steel, oil refining, fertilizers, inorganic chemicals, ferroalloys, glass manufacturing, meat processing and feed production discharge industrial wastewater containing ammonia nitrogen, and fresh wastewater such as leather and animal excrement The initial content of ammonia nitrogen is not high, but due to the deamination reaction of nitrogen in the wastewater, the concentration of ammonia nitrogen will increase rapidly after the wastewater is stored or stays in the drainage pipe for a period of time.

Organic nitrogen industrial wastewater can be treated biologically. While microorganisms remove organic carbon, oxidation converts the nitrogen in the wastewater into ammonia nitrogen through biological assimilation and biomineralization. Ammonia nitrogen wastewater treatment methods include steam stripping, air stripping, ion exchange, activated carbon adsorption, biological nitrification and denitrification.

　4. Phosphorus and organic phosphorus

　The main sources of phosphorus in domestic sewage are the use of phosphorus-containing washing products, human excrement, and domestic garbage. Washing products mainly use sodium phosphate and polymerized sodium phosphate. The phosphorus in the detergent flows into the water body with the sewage. Industrial wastewater is one of the main factors causing excessive phosphorus in water bodies. It has the characteristics of high concentration of pollutants, many types of pollutants, difficulty in degradation, and complex composition. If industrial wastewater is directly discharged without treatment, it will have a huge impact on water bodies and have adverse effects on the environment and residents' health.

Phosphorus removal generally involves biochemical methods using phosphorus-accumulating bacteria (AO, A2O, oxidation ditch, etc.) and chemical phosphorus removal (PAC, PFS, etc.), and some industrial wastewater contains Hypophosphorus and organic phosphorus must be oxidized for normal phosphorus removal.

5. Acid-alkali wastewater

High-concentration acid-alkali wastewater comes from a wide range of sources, such as chemical industry, chemical fiber, acid production, electroplating, oil refining and metal Processing plants, pickling workshops, etc. will discharge acidic wastewater. Some wastewater contains inorganic acids such as sulfuric acid and hydrochloric acid, while others contain organic acids such as formic acid and acetic acid, and some contain both.

The acid concentration of wastewater varies greatly, ranging from less than 1% to more than 10%. Production processes such as papermaking, printing and dyeing, tanning, and metal processing will discharge alkaline wastewater, which in most cases contains inorganic alkali, but also contains organic alkali. The alkali concentration of some wastewater can be as high as several percent. In addition to acids and alkalis, wastewater may also contain acid salts, basic salts, and other acidic or alkaline inorganic and organic substances.

Random discharge of wastewater containing acid and alkali will not only cause pollution and damage to the environment, but also a waste of resources. Therefore, recycling and comprehensive utilization of acid and alkali wastewater should be considered first.

When the concentration of acid and alkali wastewater is high, for example, when the acid content of acidic wastewater reaches more than 4% and the alkali content of alkali-containing wastewater reaches more than 2%, there will be recycling and synthesis The possibility of utilization can be used to make ferrous sulfate, gypsum, and fertilizers, and can also be reused or used in other factories. Acidic wastewater with a concentration lower than 4% and alkaline wastewater with a concentration lower than 2% will be neutralized since their recycling is of little significance.

6. Oil pollutants

The main industrial sources of high-concentration oily wastewater are the petroleum industry, petrochemical industry, textile industry, and metal processing industry and food processing industries. Petroleum pollutants will be produced during the process of oil extraction, refining, storage, transportation or use of petroleum products; wastewater discharged from meat processing, milk processing, laundry, car repair and other processes also contain oil or grease.

In general domestic sewage, grease accounts for about 10% of the total organic matter, and each person produces about 15g of grease every day. Except for heavy tar, which has a relative density of more than 1.1, the oils contained in the wastewater are all less than 1. Therefore, the focus of sewage treatment of oily wastewater is to remove oils with a relative density less than 1.

The types of oil pollutants in wastewater can be divided into 5 physical forms according to their existence forms.

　　(1) Free oil can quickly rise to the liquid surface to form an oil film or oil layer when it is stationary. The particle size of this oil droplet is larger, generally greater than 100μm, accounting for about the total amount of oil in wastewater. 60%-80% of the amount.

　(2) Mechanically dispersed oil, oil droplets with particle sizes generally ranging from 10 μm to 100 μm, are not very stable in wastewater and can often interact with each other after standing for a period of time. Combine to form an oil slick.

　　(3) Emulsified oil droplets, the particle size is less than 10μm, generally 0.1-2μm. This kind of oil droplets has a high degree of chemical stability, often due toWater contains surfactants to form stable emulsions.

　(4) The dissolved oil is extremely finely dispersed oil droplets. The particle size of the oil droplets is smaller than that of micro-electrolytic emulsified oil, and some can be as small as several nm, which is a chemical concept. Oil that actually dissolves in wastewater.

　(5) Solid attached oil, oil droplets adsorbed on the surface of solid particles in wastewater.

Oil in wastewater exists in different forms, and the degree of treatment is different. The treatment methods and devices used are also different. Commonly used oil and water separation methods include grease traps, ordinary oil removal tanks, coagulation oil removal tanks, coarse-grained coalescence oil removal methods, air flotation oil removal methods, etc.

7. Pathogenic microorganisms

It is generally believed that the pathogenic microorganisms in wastewater include bacteria, viruses, rickettsiae, protozoa and Five types of fungi. Rickettsia is between bacteria and viruses. Some microbiologists classify the pathogenic spirochetes represented by Pallidum as the sixth pathogenic microorganism, and spirochetes are between bacteria and protozoa. Some microorganisms that are higher than protozoa, such as nematodes, can also cause disease. Domestic sewage and industrial wastewater from slaughtering, biological products, hospitals, tanning, scouring, etc. often contain these pathogenic microorganisms that can transmit various diseases.

It is best to carry out separate disinfection treatment for sewage with relatively concentrated pathogenic pathogens and large content, and then carry out secondary biochemical treatment together with other sewage, which can reduce the consumption of disinfectants. Because pathogens survive in water for a long time, some viruses and parasite eggs are difficult to kill with ordinary disinfection methods.

Methods for disinfection and sterilization include chlorine, chlorine dioxide, ozone and other oxidation methods, lime treatment, ultraviolet irradiation, heat treatment, ultrasonic waves, etc. In addition, ultrafiltration treatment can also remove most of the pollutants in the water. bacteria. As far as the removal of bacteria and viruses is concerned, methods such as ozone oxidation and ultraviolet irradiation are very effective. However, there is no residual disinfectant similar to residual chlorine in the treated water, which cannot prevent the reproduction of microorganisms. It is usually necessary to add chlorine after treatment. deal with.

8. Nitrates and nitrites

Microelectrolytic filler fertilizer manufacturing, steel production, gunpowder manufacturing, feed production, meat processing, electronics Wastewater discharged from industries such as component and nuclear fuel production contains high concentrations of nitrates and nitrites. Some industrial wastewaters containing organic nitrogen or ammonia nitrogen may not initially contain these, but when these wastewaters are subjected to aerobic biological treatment, they may be converted into nitrates or nitrites.

Nitrite is an intermediate product of the nitrogen cycle and has poor stability in water.It can be oxidized to nitrate under the action of oxygen and microorganisms, and can be reduced to ammonia under anoxic or anaerobic conditions. Therefore, in clean water, the content of nitrite is very low. The representative product of the final stage of inorganic decomposition of nitrogen-containing organic matter is nitrate. Therefore, when the nitrogen in the water is mainly in the form of nitrate, it indicates that the content of nitrogen-containing organic matter in the water is very small and the water body has reached self-purification.

If the water contains more nitrates and various other nitrogen-containing compounds, it indicates that the self-purification process of the water body is ongoing or the water body is being polluted by nitrate wastewater. Simultaneously measuring three types of inorganic nitrogen such as ammonia nitrogen, nitrite nitrogen and nitrate nitrogen in the body and combining the analysis results of organic nitrogen and total nitrogen can analyze the degree of pollution of the water body by nitrogenous compounds and the self-purification status.

The analysis results of these nitrogen compounds can also be used to judge the effect of sewage treatment and guide the adjustment of the operation of the denitrification process. Nitrite can react with secondary ammonium in the stomach to form a strong carcinogen, and nitrate can be reduced to nitrite in the human body. Therefore, drinking water with a high nitrate concentration is also harmful to human health. Children drinking water with high nitrate content will increase the denatured hemoglobin in the blood and cause poisoning.

Therefore, relevant national standards stipulate the nitrate concentration in water bodies. Among them, the drinking water hygiene standard stipulates that the maximum allowable concentration is 20mg/L in N, and the surface water quality standard GB 3838-2002 It is stipulated that the maximum allowable concentration of nitrate in centralized domestic drinking water surface water sources is 10mg/L (calculated as N).

The conventional method for treating industrial wastewater containing nitrate or nitrite is micro-electrolytic filler biological denitrification and denitrification. For a small amount of industrial wastewater containing nitrate or nitrite, electrodialysis, reverse osmosis, ion exchange and other methods can also be used.

9. Fluoride

Manufacturing of fluorine-containing products, coke production, electronic component production, electroplating, glass and silicate production, steel Industrial wastewater containing fluoride will be discharged during processes such as aluminum manufacturing, metal processing, wood preservation, and pesticide and fertilizer production.

The treatment methods for fluoride-containing wastewater can be divided into two categories: precipitation and adsorption. The precipitation method is suitable for treating industrial wastewater with high fluoride content, but incomplete treatment by the precipitation method often requires secondary treatment. The chemicals required for treatment include lime, alum, dolomite, etc. The adsorption method is suitable for treating industrial wastewater with low fluoride content or wastewater whose fluoride concentration still cannot meet relevant regulations after precipitation treatment.

10. Sulfides

Oil refining and textilesIn the production process of printing and dyeing, coke, gas, pulp, leather and various chemical raw materials, industrial wastewater containing sulfide will be discharged. Wastewater containing sulfate can also be reduced to produce sulfide under anaerobic conditions and become sulfide-containing wastewater. of wastewater.

The treatment methods for sulfide-containing wastewater include converting sulfide into sulfide salt for flocculation and precipitation, and converting sulfide into hydrogen sulfide for stripping.

11. Cyanide

Natural waters generally do not contain cyanide. If hydrogen cyanide is found in the water, it must be caused by human activities. of.

The main source of cyanide in water is industrial pollution. Cyanide and hydrocyanic acid are widely used industrial raw materials. Mining and refining, photographic printing, electroplating, metal surface treatment, coke ovens, gas, dyes, tanning, plastics, synthetic fibers and industrial gas washing and other industries all discharge cyanide-containing wastewater. . In addition, the catalytic cracking and coking processes of petroleum will also discharge cyanide-containing wastewater, among which the electroplating industry is the industry that discharges the most cyanide-containing wastewater.

Commonly used treatment methods are chlorine oxidation, ozone oxidation and electrolytic oxidation. When treating cyanide-containing wastewater, a certain amount of oxidant sodium hypochlorite is usually added, which is first converted into cyanogen chloride and then hydrolyzed into cyanate. Then it is oxidized into carbon dioxide and nitrogen under alkaline conditions and converted into ammonium salt under acidic conditions.

12. Phenol

Industries such as oil refining, chemicals, explosives, resins, and coking will discharge phenol-containing wastewater, among which the wastewater discharged by indigenous coking methods The concentration of phenol in wastewater is high. In addition, industries such as machinery maintenance, foundry, papermaking, textile, ceramics, and coal-to-gas production also release large amounts of phenol-containing wastewater.

The treatment methods for high phenolic wastewater include extraction, activated carbon adsorption and incineration.

Methods for treating medium-concentrated water include biological methods, activated carbon adsorption methods, and chemical oxidation methods.

Low-concentration phenol-containing wastewater can also be treated by ozone oxidation or activated carbon adsorption.

13. Silver

Silver is a precious metal with a silvery white color. The soluble component of common silver salts is silver nitrate, which is also the main component of silver in wastewater. Silver nitrate is widely used in radio, chemical industry, machine manufacturing, ceramics, photography, electroplating, and ink manufacturing industries. The main sources of silver-containing wastewater are the electroplating industry and the photography industry.

The basic methods for removing silver from wastewater include precipitation, ionThere are four methods: exchange method, reduction substitution method and electrolytic recovery method. Adsorption method, reverse osmosis method and electrodialysis method are also used. Because the economic value of recovering silver from wastewater is high, in order to achieve a high recovery rate, multiple methods are often used in combination. For example, electroplating wastewater containing more silver can be more completely recovered through ion exchange, evaporation or electrolytic reduction.

　14. Nickel

Microelectrolytic nickel is a silver-white metal with good ductility and high magnetism. Nickel in wastewater mainly exists in the form of divalent ions, such as nickel sulfate, nickel nitrate, and nickel salts formed with many inorganic and organic complexes.

There are many industrial sources of nickel-containing wastewater, mainly the electroplating industry, in addition to mining, metallurgy, machine manufacturing, chemistry, instrumentation, petrochemicals, textiles and other industries, as well as steel plants and iron foundries. Wastewater discharged from , automobile, and aircraft manufacturing, printing, ink, ceramics, glass and other industries also contains nickel.

Methods for treating nickel-containing wastewater include micro-lime precipitation or sulfide precipitation, ion exchange, reverse osmosis, evaporation recovery, etc.

15. Lead

Pure lead is gray-white and is one of the non-ferrous metals widely used in industry. It is often used as raw material for batteries, electroplating, pigments, rubber, pesticides, fuels, paints, lead glass, explosives, matches and other manufacturing industries. The acidic wastewater discharged from the lead plate manufacturing process has a high lead concentration, and the wastewater produced by the electroplating industry dumping electroplating waste liquid has a high lead concentration.

Common methods for treating lead-containing wastewater include precipitation, coagulation, adsorption, galvanic iron oxidation, etc.

16. Chromium

Pure chromium is a steel-gray corrosion-resistant metal with relatively high hardness. With the development of industry, the application of chromium and its compounds is becoming more and more widespread, and the discharge of chromium-containing wastewater is increasing. Chromium-containing series corrosion inhibitors are one of the most effective agents in circulating cooling systems and have been used on a large scale.

The manufacturing of inks, dyes and paint pigments, as well as industries such as chromium leather tanning, electroplating, aluminum anodizing and other metal cleaning, are all inseparable from chromium compounds. Chromium compounds can also be used as wood fire retardants and fire retardants. The production wastewater discharged from these industries naturally contains different amounts of chromium. Chromium exists in the form of hexavalent (CrO42-) and trivalent (CrO2-) ions in the water. Industrial wastewater mainly exists in the hexavalent form.

The treatment method for chromium-containing wastewater is to first reduce hexavalent chromium to trivalent chromium.The trivalent chromium is then precipitated to generate hydroxide and then removed. Evaporation recovery of high-concentration chromium-containing wastewater is a technically and economically feasible method for high-concentration organic wastewater. The ion exchange method can reduce the discharge concentration of chromium-containing wastewater to a lower level.

17. Mercury

Mercury, also known as mercury, is a silver-white liquid metal with sublimation properties. Because mercury has some special physical and chemical properties, it is widely used in the production of chlor-alkali, electronics, petrochemicals, chemicals, smelting, instrumentation, papermaking, explosives, pesticides, textiles, printing and dyeing, fertilizers, electrical appliances, pharmaceuticals, paints, fur processing and other industries. in process. For example, in the chemical and petrochemical industries, mercury is used as a catalyst in plastic production and reactions such as hydrogenation, dehydrogenation, and sulfonation. The production wastewater discharged by these industries naturally contains varying amounts of mercury.

Common methods for treating mercury-containing wastewater include sulfide precipitation, micro-electrolysis ion exchange, adsorption coagulation, reduction filtration, activated carbon adsorption, and microbial concentration.

18. Organochlorines

Organochlorine compounds include chlorinated alkanes, chlorinated alkenes, chlorinated aromatic hydrocarbons and organochlorine pesticides, etc. Among them, organochlorine pesticides and polychlorinated biphenyls have a greater impact on the environment, mainly from wastewater discharged from pesticides, dyes, plastics, synthetic rubber, chemicals, chemical fibers and other industries.

Organochlorine wastewater is mainly treated by incineration. The incineration products are hydrogen chloride and carbon dioxide. In order to recover and treat the hydrogen chloride produced by incineration, the specific methods of incineration include incineration-flue gas alkali neutralization method, Incineration - recovery of anhydrous hydrogen chloride method and incineration - flue gas recovery of hydrochloric acid method.

19. Benzopyrene

Benzopyrene, referred to as BaP, is a representative strong carcinogenic condensed aromatic hydrocarbon among polycyclic aromatic hydrocarbons (PAH). The sources of BaP in natural water can be divided into artificial sources and natural sources. The former mainly comes from the incomplete combustion of organic matter, and the latter mainly comes from the biosynthesis of natural laws. Therefore, BaP exists to varying degrees in industries with incomplete combustion of organic matter, such as oil refining, coking, and other industrial wastewater, as well as wastewater discharged from ammonia plants, brick factories, airports, etc.

Although BaP is highly toxic, it is relatively simple and easy to remove. The oxidation of ozone, liquid chlorine, chlorine dioxide, activated carbon adsorption, flocculation sedimentation and activated sludge treatment can all be effective. Remove BaP from wastewater.

20. Cadmium

Cadmium is a gray-white metal.It mainly exists in bivalent form in nature. Cadmium electroplating can provide an anti-corrosion protective layer for steel, iron, etc. It has the characteristics of good adsorption and uniform and smooth coating. Therefore, 90% of cadmium in industry is used in electroplating, pigments, plastic stabilizers, alloys and batteries. In other industries, the sources of cadmium-containing wastewater also include the production processes of metal mining, smelting, electrolysis, pesticides, medicines, paints, alloys, ceramics and inorganic pigment manufacturing, electroplating, textile printing and dyeing and other industries.

The treatment methods for cadmium-containing wastewater include hydroxide or sulfide precipitation method, adsorption method, ion exchange method, redox method, ferrite method, membrane separation method and biochemical method, etc. For cadmium-containing wastewater with high concentration or concentration after ion exchange, electrolysis and evaporation recovery method is also a practical method.

　21. Arsenic

Arsenic has a gray metallic luster and is insoluble in water, but there are a variety of arsenic compounds that are easily soluble in water. Inorganic arsenic mainly exists in water in the form of arsenite ions and arsenate ions. In the presence of dissolved oxygen, arsenite can be oxidized into less toxic arsenate. Arsenic acid and arsenate are found in industrial wastewater from industries such as metallurgy, glassware, ceramics, leather, chemicals, fertilizers, petroleum refining, alloys, sulfuric acid, fur, dyes and pesticides.

Conventional treatment methods for arsenic include lime or sulfide precipitation, or co-precipitation with iron or aluminum hydroxides. The traditional flocculation process of wastewater treatment can also effectively remove arsenic in wastewater. In addition, the use of activated carbon or alumina adsorption and ion exchange to remove arsenic from wastewater has also achieved varying degrees of success.

In recent years, research on the use of biochemical methods to treat arsenic-containing wastewater has made progress. Experiments have proven that the activated sludge method can remove arsenic extremely quickly, and the total amount of arsenic can be removed within 0.5 hours. About 80%, reaching an equilibrium state in about 1 to 2 hours, that is, a large amount of arsenic removal effect can be achieved after a short time of contact with sludge. However, the removal rate of activated sludge for low-concentration arsenic is significantly higher than the removal rate for high-concentration arsenic, which also shows that the removal ability of sludge for arsenic is also limited.

　(Original title: Dry information! The sources and treatment methods of 21 common pollutants in sewage treatment!)