2. How to treat mercury-containing wastewater and what are the characteristics of mercury-containing compounds?
Mercury-containing wastewater mainly comes from nonferrous metal smelters, chemical plants, pesticide plant, paper mills, dye factories and thermal instrumentation factories. The methods of removing inorganic mercury from wastewater include sulfide precipitation, chemical coagulation, activated carbon adsorption, metal reduction, ion exchange and microbial method. Generally, alkaline mercury-containing wastewater is usually treated by chemical coagulation or sulfide precipitation. Acidic wastewater containing mercury can be treated by metal reduction. Low-concentration mercury-containing wastewater can be treated by activated carbon adsorption, chemical coagulation or activated sludge process, while organic mercury wastewater is difficult to treat. Usually, organic mercury is oxidized to inorganic mercury first, and then treated.
the toxicity of various mercury compounds varies greatly. Elemental mercury is basically non-toxic; Mercury mercuric chloride in inorganic mercury is a highly toxic substance, while phenylmercury in organic mercury decomposes quickly and has little toxicity. Methylmercury is easily absorbed into human body, not easily degraded and excreted slowly, especially easily accumulated in brain. The most toxic, such as Minamata disease is caused by methyl mercury poisoning.
3. What are the characteristics of oily wastewater and how to treat it?
oily wastewater mainly comes from petroleum, petrochemical, steel, coking, gas generating station, mechanical processing and other industrial sectors. The relative density of oily pollutants in wastewater is less than 1 except that of heavy tar is above 1.1. Oils usually exist in three States in wastewater. (1) oil is floated, and the oil droplet size is greater than 1? M, which is easy to be separated from wastewater. (2) Dispersed oil. The oil droplet size is between 1 and 1? M, floating in the water. (3) emulsified oil, the oil droplet size is less than 1? M is not easy to be separated from wastewater. Because of the great difference of oil concentration in wastewater discharged from different industrial sectors, for example, the oil content in wastewater produced during oil refining is about 15-1mg/L, the tar content in coking wastewater is about 5-8mg/L, and the tar content in wastewater discharged from gas generating stations can reach 2-3mg/L.. Therefore, the treatment of oily wastewater should first use the grease trap to recover the floating oil or heavy oil, the treatment efficiency is 6%-8%, and the oil content in the effluent is about 1-2 mg/L; Emulsified oil and dispersed oil in wastewater are difficult to treat, so emulsifying phenomenon should be prevented or reduced. One of the methods is to pay attention to reducing the emulsification of oil in wastewater during production; Secondly, in the process of treatment, try to reduce the number of times of pumping wastewater to avoid increasing the degree of emulsification. Treatment methods usually adopt air flotation and demulsification.
4. What are the sources of heavy metal wastewater and its treatment principles?
The heavy metal wastewater mainly comes from the wastewater discharged by enterprises such as mines, smelting, electrolysis, electroplating, pesticides, medicines, paints and pigments. The types, contents and existing forms of heavy metals in wastewater vary with different production enterprises. Because heavy metals cannot be decomposed and destroyed, they can only transfer their existing positions and transform their physical and chemical forms. For example, after chemical precipitation treatment, heavy metals in wastewater are transformed from dissolved ions to insoluble substances and precipitated, and then transferred from water to sludge; After ion exchange treatment, heavy metal ions in wastewater are transferred to ion exchange resin, and then transferred from ion exchange resin to regenerated waste liquid after regeneration. Therefore, the principles of heavy metal wastewater treatment are as follows: firstly, the most fundamental thing is to reform the production process, not to use or use less toxic heavy metals; Secondly, reasonable technological process, scientific management and operation are adopted to reduce the amount of heavy metals and the amount lost with wastewater and minimize the amount of discharged wastewater. Heavy metal wastewater should be treated on the spot where it is produced, and it should not be mixed with other wastewater to avoid complicating the treatment. It should not be discharged directly into urban sewers without treatment, so as not to expand heavy metal pollution. The treatment of heavy metal wastewater can usually be divided into two categories; Firstly, the dissolved heavy metals in wastewater are transformed into insoluble metal compounds or elements, which are removed from wastewater by precipitation and floating. The methods can be applied, such as neutralization precipitation, sulfide precipitation, floating separation, electrolytic precipitation (or floating) and diaphragm electrolysis. The second is to concentrate and separate the heavy metals in wastewater without changing their chemical forms. The applicable methods include reverse osmosis, electrodialysis, evaporation and ion exchange. These methods should be used alone or in combination according to the quality and quantity of wastewater.
5. How to treat cyanide-containing wastewater?
cyanide-containing wastewater mainly comes from electroplating, gas, coking, metallurgy, metal processing, chemical fiber, plastics, pesticides, chemical industry and other departments. Cyanide-containing wastewater is a kind of industrial wastewater with great toxicity, which is unstable in water and easy to decompose. Inorganic cyanide and organic cyanide are highly toxic substances, which can cause acute poisoning if ingested by people. The lethal dose of cyanide to human body is .18, potassium cyanide is .12 g, and the lethal concentration of cyanide to fish in water is .4-.1 mg/L. The treatment measures of cyanide-containing wastewater mainly include: (1) reforming the process to reduce or eliminate cyanide-containing wastewater, such as cyanide-free electroplating, which can eliminate industrial wastewater in electroplating workshop. (2) Waste water with high cyanide content should be recycled, and waste water with low cyanide content should be purified before being discharged. Recovery methods include acidification aeration-alkali absorption method, steam desorption method, etc. Treatment methods include alkaline chlorination, electrolytic oxidation, pressure hydrolysis, biochemistry, bio-iron, ferrous sulfate, air stripping and so on. Among them, the basic chlorination method is widely used, the ferrous sulfate method is not thorough and unstable, and the air stripping method not only pollutes the atmosphere, but also fails to meet the discharge standard.
6. What are the characteristics of pesticide wastewater and its treatment methods?
There are many kinds of pesticides, and the quality of pesticide wastewater is complicated. Its main characteristics are: (1) the concentration of pollutants is high, and the chemical oxygen demand (COD) can reach tens of thousands of mg per liter; (2) It is highly toxic. Besides pesticides and intermediates, the wastewater also contains toxic substances such as phenol, arsenic and mercury, as well as many biodegradable substances. (3) It has a foul smell and is irritating to human respiratory tract and mucous membrane; (4) The water quality and quantity are unstable. Therefore, the pollution of pesticide wastewater to the environment is very serious. The purpose of pesticide wastewater treatment is to reduce the concentration of pollutants in pesticide production wastewater, improve the recycling rate, and strive to achieve harmlessness. The treatment methods of pesticide wastewater include activated carbon adsorption, wet oxidation, solvent extraction, distillation and activated sludge. However, developing 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 organomercury pesticides such as HCH, and actively studied and used microbial pesticides, which is a new way to fundamentally prevent pesticide wastewater from polluting the environment.
7. What are the characteristics of wastewater pollution in food industry and its treatment methods?
The food industry has a wide range of raw materials and products, and the quantity and quality of wastewater discharged are quite different. The main pollutants in wastewater are (1) solid substances floating in wastewater, such as vegetable leaves, peels, minced meat, poultry feathers, etc. (2) The substances suspended in the waste water include grease, protein, starch, colloidal substances, etc. (3) Acid, alkali, salt, sugar, etc. dissolved in wastewater: (4) Mud, sand and other organic matters entrained in raw materials; (5) Pathogenic bacteria and viruses. The wastewater from food industry is characterized by high content of organic matter and suspended solids, easy to rot and generally non-toxic. Its harm is mainly to make the water body eutrophic, so as to cause the death of aquatic animals and fish, promote the odor of organic matter deposited at the bottom of the water, worsen the water quality and pollute the environment.
besides proper pretreatment according to the characteristics of water quality, biological treatment is generally suitable for food industry wastewater treatment. If the effluent quality is very high or the organic matter content in wastewater is high, two-stage aeration tank or two-stage biofilter, or multi-stage biological turntable can be used, or two biological treatment devices can be used in combination, or an anaerobic-aerobic biological treatment system can be used in series.
8. How to treat the wastewater from paper industry?
papermaking wastewater mainly comes from two production processes: pulping and papermaking. Pulping is to separate fibers from plant raw materials, make them into pulp, and then bleach them; Papermaking is to dilute, shape, press and dry the pulp to make paper. Both processes discharge a lot of wastewater. The wastewater from pulping is the most polluted. The wastewater discharged during pulp washing is dark brown, which is called black water. The concentration of pollutants in black water is very high, with BOD as high as 5-4g/L, containing a lot of fibers, inorganic salts and pigments. The wastewater discharged from bleaching process also contains a lot of acid and alkali substances. The waste water discharged from papermaking machine is called white water, which contains a lot of fibers and fillers and rubber compounds added in the production process. The treatment of wastewater from papermaking industry should focus on improving the recycling rate, reducing the water consumption and wastewater discharge, and at the same time, we should actively explore various reliable, economical and effective treatment methods that can make full use of useful resources in wastewater. For example, the flotation method can recover fibrous solid substances from white water, and the recovery rate can reach 95%, and the clarified water can be reused; Sodium hydroxide, sodium sulfide, sodium sulfate and other sodium salts combined with organic matter can be recovered from black water by combustion method. Neutralization method adjusts pH value of wastewater; Coagulation sedimentation or flotation can remove suspended solids from wastewater; Chemical precipitation method can decolorize; Biological treatment can remove BOD, which is effective for kraft paper wastewater; Wet oxidation process is successful in treating sulfite pulp wastewater. In addition, reverse osmosis, ultrafiltration and electrodialysis are also used at home and abroad.
9. How to treat printing and dyeing wastewater?
The printing and dyeing industry consumes a lot of water, usually 1-2 t per 1t of textile processing, of which 8-9% is discharged by printing and dyeing wastewater. Commonly used treatment methods include recycling and harmless treatment.
Recycling:
(1) Wastewater can be recycled according to the water quality characteristics, such as the separation of bleaching and boiling wastewater and dyeing and printing wastewater. The former can be washed by convection, which can reduce the discharge.
(2) The alkali liquor is usually recovered by evaporation. If the alkali liquor is large, it can be recovered by triple-effect evaporation, and if the alkali liquor is small, it can be recovered by film evaporation.
(3) dye recovery. For example, the schilling dye can be acidified into cryptobutyric acid in colloidal particles, suspended in the residual liquid, and recycled after precipitation and filtration.
Harmless treatment can be divided into:
(1) Physical treatment methods include precipitation and adsorption. Precipitation mainly removes suspended solids from wastewater; Adsorption is mainly used to remove dissolved pollutants and decolorize wastewater.
(2) Chemical treatment methods include neutralization, coagulation and oxidation. Neutralization is to adjust the pH value of wastewater and reduce the chromaticity of wastewater. Coagulation method is to remove dispersed dyes and colloidal substances from wastewater; The oxidation method is to oxidize the reducing substances in wastewater, so that sulfide dyes and vat dyes can be precipitated.
(3) Biological treatment methods include activated sludge, biological rotary table, biological rotary drum and biological contact oxidation. In order to improve the effluent quality and meet the discharge standards or recovery requirements, it is often necessary to adopt several methods for joint treatment.
1. How to treat dye production wastewater?
Wastewater from dye production contains acids, bases, salts, halogens, hydrocarbons, amines, nitro compounds, dyes and their intermediates, and some also contain pyridine, cyanide, phenol, benzidine and heavy metals such as mercury, cadmium and chromium. These wastewater are complex and toxic, so it is difficult to treat. Therefore, the treatment of dye production wastewater should be based on the characteristics of wastewater and its discharge requirements, and appropriate treatment methods should be selected. For example, coagulation and filtration can be used to remove solid impurities and inorganic substances; Chemical oxidation, biological method and reverse osmosis are mainly used to remove organic matter and toxic substances. Generally, decoloration can be carried out by coagulation and adsorption, and heavy metals can be removed by ion exchange.
11. how to treat chemical industry wastewater?
Chemical industrial wastewater mainly comes from production wastewater discharged from petrochemical industry, coal chemical industry, acid-base industry, fertilizer industry, plastic industry, pharmaceutical industry, dye industry and rubber industry. The main measures for the prevention and control of chemical wastewater pollution are as follows: firstly, we should reform the production technology and equipment, reduce pollutants, prevent wastewater from being discharged, and comprehensively utilize and recycle it; The treatment degree of wastewater that must be discharged should be selected according to the water quality and requirements. The primary treatment mainly separates suspended solids, colloids, oil slick or heavy oil from water. Methods such as water quality and quantity adjustment, natural sedimentation, floating and oil separation can be adopted. Secondary treatment is mainly to remove biodegradable organic dissolved substances and some colloids, reduce biochemical oxygen demand and some chemical oxygen demand in wastewater, and usually adopts biological treatment. After biological treatment, there is still a considerable amount of COD in the wastewater, sometimes with high color, smell and taste, or because of the high requirements of environmental hygiene standards, it is necessary to adopt the three-stage treatment method for further purification. 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 industrial wastewater can be treated by different methods according to different water quality and quantity and the requirements of treated effluent quality.
12. What are the characteristics of acid-base wastewater and its treatment principles?
Acid wastewater mainly comes from iron and steel plants, chemical plants, dye plants, electroplating plants and mines, etc., which contains various harmful substances or heavy metal salts. The mass fraction of acid varies greatly, ranging from less than 1% to more than 1%. Alkaline wastewater mainly comes from printing and dyeing factories, leather factories, paper mills and oil refineries. Some of them contain organic alkali or inorganic alkali. The mass fraction of alkali is higher than 5% and lower 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 has strong corrosiveness, and can only be discharged after proper treatment. The first principle of treating acid-base wastewater is as follows: (1) High-concentration acid-base wastewater should be given priority to recycling. According to water quality, water quantity and different process requirements, plant or regional scheduling should be carried out to reuse it as much as possible. If it is difficult to reuse it, or the concentration is low and the water quantity is large, the acid-base can be recycled by concentration. (2) Low-concentration acid-base wastewater, such as washing water in pickling tank and rinsing water in alkali washing tank, should be neutralized.
for neutralization treatment, the principle of treating waste with waste should be considered first. For example, acid and alkali wastewater neutralize each other or use waste alkali (slag)