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Industrial Wastewater Treatment Section 2

Upload time:2021-07-07

What are the characteristics of food industry waste sewage pollution and its treatment methods?
The food industry has a wide range of raw materials and a wide variety of products, and the amount and quality of discharged waste water vary greatly. The main pollutants in the wastewater include:
(1) solid substances floating in the wastewater, such as vegetable leaves, peels, minced meat, poultry feathers, etc.;
(2) substances suspended in the wastewater include oil, protein, starch, colloidal substances, etc.;
(3) Acids, alkalis, salts, sugars, etc. dissolved in wastewater;
(4) Mud, sand and other organic matter entrained in raw materials;
(5) Pathogenic bacteria, etc.
Food industry wastewater is characterized by high content of organic matter and suspended solids, perishable, and generally no large toxicity.
The main harm is to make the water body eutrophication, causing the death of aquatic animals and fish, and promoting the organic matter deposited on the bottom to produce odor, deteriorating water quality and polluting the environment.
In addition to proper pretreatment according to the characteristics of water quality, the wastewater treatment in the food industry should generally adopt biological treatment. If the effluent quality is very high or the organic matter content in the wastewater is high, a two-stage aeration tank or a two-stage biological filter, or a multi-stage biological turntable can be used. Or a combination of two biological treatment devices can also be used anaerobic -Aerobic series connection. 
How to treat wastewater from the paper industry?    Papermaking wastewater mainly comes from the two production processes of pulping and papermaking in the papermaking industry. Pulping is to separate the fibers from plant raw materials into a slurry, and then bleach it; papermaking is to dilute, shape, squeeze, and dry the slurry to make paper. Both processes discharge large amounts of waste water.    Wastewater from pulping is the most polluted. The waste water discharged during washing is dark brown, called black water. The concentration of pollutants in the black water is very high, the BOD is as high as 5-40g/L, and it contains a lot of fibers, inorganic salts and pigments.
The wastewater discharged from the bleaching process also contains a large amount of acid and alkali substances. The waste water discharged from the paper machine is called white water, which contains a large amount of fibers and fillers and rubber materials added during the production process.
The treatment of wastewater from the paper industry should focus on increasing the recycling rate, reducing water consumption and wastewater discharge, and actively exploring various reliable, economical, and capable of making full use of useful resources in wastewater treatment methods.
For example, the flotation method can recover fibrous solids in white water, the recovery rate can reach 95%, and the clarified water can be reused; the combustion method can recover sodium hydroxide, sodium sulfide, sodium sulfate and other sodium salts combined with organic matter in black water. Neutralization method adjusts the pH value of wastewater; coagulation sedimentation or flotation method can remove suspended solids in wastewater; chemical precipitation method can decolorize; biological treatment method can remove BOD, which is more effective for kraft paper wastewater; wet oxidation method is more effective for sulfite pulp wastewater treatment success. In addition, treatment methods such as reverse osmosis, ultrafiltration, and electrodialysis are also used at home and abroad.
How to treat wastewater from printing and dyeing industry?
The printing and dyeing industry consumes a lot of water, usually 100 to 200 tons of water per 1 ton of textiles during printing and dyeing. 80% to 90% of it is discharged as printing and dyeing wastewater. Commonly used treatment methods include recycling and harmless treatment.
Recycling:
(1) Waste water can be recycled according to water quality characteristics, such as the diversion of bleaching and smelting wastewater and dyeing and printing wastewater. The former can be washed by convection. One water is used for multiple purposes, reducing emissions;
(2) Lye recycling, usually used Evaporation method recovery, if the amount of lye is large, it can be recovered by three-effect evaporation, and the amount of lye is small, and it can be recovered by thin film evaporation;
(3) Dye recovery. For example, Shihlin dye can be acidified into cryptopic acid, which is colloidal particles. Suspended in the residue The liquid is recovered and reused after precipitation and filtration.
The harmless treatment can be divided into:
(1) The physical treatment methods include precipitation method and adsorption method. The precipitation method mainly removes suspended solids in wastewater; the adsorption method mainly removes dissolved pollutants and decolorization in wastewater.
(2) Chemical treatment methods include neutralization method, coagulation method and oxidation method. The neutralization method is to adjust the pH in the wastewater, and can also reduce the chromaticity of the wastewater; the coagulation method is to remove the disperse dyes and colloidal substances in the wastewater; the oxidation method is to oxidize the reducing substances in the wastewater to precipitate the sulfur dyes and vat dyes.
(3) Biological treatment methods include activated sludge, biological turntable, biological rotary drum and biological contact oxidation method. In order to improve the quality of effluent water, it is often necessary to adopt several methods for joint treatment to meet discharge standards or recycling requirements.
How to treat dye production wastewater?
Dye production wastewater contains acids, alkalis, 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 components are complex and toxic, and difficult to treat. Therefore, the treatment of dye production wastewater should select appropriate treatment methods according to the characteristics of the wastewater and its discharge requirements. For example: to remove solid impurities and inorganic substances, coagulation and filtration methods can be used; to remove organic and toxic substances, chemical oxidation, biological methods and reverse osmosis methods are mainly used; decolorization can generally use coagulation and adsorption processes. In the process, the ion exchange method can be used to remove heavy metals.
How to treat chemical industry wastewater?
The chemical industry wastewater mainly comes from the production wastewater discharged from the 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: first of all, the production process and equipment should be reformed, pollutants should be reduced, wastewater should be prevented from being discharged, and comprehensive utilization and recycling should be carried out; the treatment level of wastewater that must be discharged should be selected according to the water quality and requirements.
The primary treatment mainly separates suspended solids, colloids, slick oil or heavy oil in the water. Methods such as water quality and quantity adjustment, natural precipitation, floating and oil separation can be used. The secondary treatment is mainly to remove the biodegradable organic dissolved matter and part of colloids, and reduce the biochemical oxygen demand and part of the chemical oxygen demand in the wastewater, usually by biological treatment. A considerable amount of COD remains in the biologically treated wastewater, sometimes with high color, smell, and taste, or because of high environmental sanitation standards, a tertiary treatment method is required for further purification. The tertiary treatment is mainly to remove organic pollutants and soluble inorganic pollutants that are difficult to biodegrade in wastewater. Commonly used methods are activated carbon adsorption method and ozone oxidation method, ion exchange and membrane separation technology can also be used. Various chemical industrial wastewater can be treated with different treatment methods according to different water quality, water volume, and external drainage quality requirements after treatment.
What are the characteristics of acid-base wastewater and its treatment principles?
Acidic wastewater mainly comes from steel plants, chemical plants, dye plants, electroplating plants and mines, etc., which contain various harmful substances or heavy metal salts. The mass fraction of acid varies greatly, the low is less than 1%, and the high is greater than 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 higher than 5%, and some 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 is highly corrosive and needs to be properly treated before it can be discharged.
The general principles for the treatment of acid-base wastewater are: (1) High-concentration acid-base wastewater should be recycled and reused first. According to water quality, water volume and different process requirements, plant or regional scheduling should be carried out to reuse as much as possible: if it is difficult to reuse, Or the concentration is low and the amount of water is large, so the concentration method can be used to recover the acid and alkali. (2) Low-concentration acid and alkali wastewater, such as the cleaning water of the pickling tank and the rinsing water of the alkali cleaning tank, should be neutralized. For disposal, the principle of waste-to-waste should be considered first. For example, acid and alkali wastewater are mutually neutralized or waste alkali (slag) is used to neutralize acidic wastewater, and waste acid is used to neutralize alkaline wastewater. In the absence of these conditions, a neutralizer can be used for treatment.
What flotation reagents are contained in the beneficiation wastewater and how to deal with them?
The beneficiation wastewater has the characteristics of large water volume, high suspended solids content, and many types of harmful substances. The harmful substances are heavy metal ions and beneficiation agents. Heavy metal ions include copper, zinc, lead, nickel, barium, cadmium, arsenic and rare elements.
The flotation reagents added in the beneficiation process are as follows:
(1) Collecting agents: such as xanthate (RocssMe), black medicine [(RO)2PSSMe], baiyao [CS(NHC6H5)2];
(2) inhibitors: such as cyanide (KCN, NaCN), water glass ( Na2SiO3);
(3) Foaming agent: such as turpentine, cresol (C6H4CH30H);
(4) Active agent: such as copper sulfate (CuS04), heavy metal salts;
(5) Vulcanizing agent: such as sodium sulfide;
(6) Mineral Regulators: such as sulfuric acid, lime, etc.
The beneficiation wastewater mainly passes through the tailing dam to effectively remove suspended solids in the wastewater, and the content of heavy metals and flotation reagents can also be reduced. If the emission requirements are not met, further treatment should be carried out. Common treatment methods are:
(1) To remove heavy metals, use lime neutralization and roasting dolomite adsorption;
(2) In addition to flotation reagents, use ore adsorption, Activated carbon adsorption method;
(3) Chemical oxidation method can be used for cyanide-containing wastewater.
Metallurgical wastewater can be divided into several categories. What is the development trend of its treatment?
The main characteristics of metallurgical wastewater are large amount of water, many types, and complex and changeable water quality. Classified according to the source and characteristics of wastewater, there are mainly cooling water, pickling wastewater, washing wastewater (dust removal, gas or flue gas), slag washing wastewater, coking wastewater, and wastewater that is condensed, separated or overflowed from production.
The development trend of metallurgical wastewater treatment is:
(1) Develop and adopt new processes and new technologies that do not use or use less water, and are pollution-free or less polluting, such as dry quenching, preheating of coking coal, and direct desulfurization from coke oven gas Decyanation, etc.;
(2) Develop comprehensive utilization technologies, such as recovering useful substances and heat energy from waste water and waste gas, and reduce material and fuel loss;
(3) According to different water quality requirements, comprehensively balance, use in series, and improve water quality stabilization measures. Improve the recycling rate of water;
(4) Develop new treatment processes and technologies suitable for the characteristics of metallurgical wastewater, such as the treatment of iron and steel wastewater by magnetic methods, which have the advantages of high efficiency, less land occupation, and convenient operation and management.

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