Analysis on preparation technology of ultra pure w

2022-08-02
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Water treatment technology - Analysis on preparation technology of ultra pure water technology

1. Development process of ultra pure water preparation

in the early stage, the demand for ultra pure water mainly came from power generation, pharmaceutical and chemical industry, papermaking and other industries, and the water quality requirements were relatively low. As long as ion exchange was used for its preparation, the main disadvantage of this method was that the regeneration of chemical agents was troublesome and uneconomical, and the forced resin had poor removal effect on general organic molecules, The TOC content in the effluent is high. With the semiconductor industrial process, the quality of ultra pure water is required to be improved, which greatly promotes the development of pure water technology. By the end of the last century, membrane technology has been widely used. Advanced water treatment technologies such as microfiltration, ultrafiltration, electrodialysis and reverse osmosis have developed rapidly. The preparation of pure water by membrane method has replaced the traditional ion exchanger system and solved the TOC problem, It meets the requirements of the electronic industry for the quality of pure water

2. Ultra pure water preparation process

1. Traditional ultra pure water preparation process:

raw water - multi-media filter - activated carbon filter - primary desalination - mixed bed - ultra pure water

2. Membrane ultra pure water preparation process:

raw water - ultrafiltration - reverse osmosis - EDI - ultra pure water

in the membrane process, ultrafiltration, microfiltration replace clarification, quartz sand filter, Activated carbon filter can remove suspended solids, colloids and organic matters in the water, reduce turbidity, SDI, COD, etc., and realize the safe and efficient operation of reverse osmosis device for sewage reuse. Reverse osmosis can replace ion exchanger desalination to further remove organic matters, colloids, bacteria and other impurities, so as to ensure that the reverse osmosis effluent meets the requirements of EDI inflow, EDI can replace the deep desalination of mixed bed, and resin regeneration can be realized by electricity rather than acid and alkali, The secondary pollution is avoided

3. Introduction to raw water quality

direct gate or large section gate can reduce the shrinkage of impurities in the water according to the deposit, but the anisotropy is large, the shrinkage along the material flow direction is small, and the shrinkage along the vertical material flow direction is large; On the contrary, when the gate thickness is small, the gate part will set and harden prematurely, and the plastic in the mold cavity can not be supplemented in time after shrinkage. The different forms of shrinkage can be divided into suspended solids, colloids and soluble solids. The solid content is indicated by the total solid content, and a certain amount of water sample is dried to constant weight in the ° oven. The weight obtained is the total solid content

the first category refers to suspended substances in water with particle diameter of more than mm, such as sediment, clay, animal and plant debris, microorganisms. In case of abnormal conditions, it must immediately shut down and cut off the power supply, report to the laboratory director and the manufacturer for maintenance. It is not allowed to disassemble the machine organic substances, algae, etc.

the second category refers to colloids, which refer to charged colloids in water. For example, the particle diameter is between mm, Colloidal particles are a collection of many molecules or ions. Such small particles have a large specific surface area, which makes them have a special adsorption capacity. The adsorbed substances are often ions in water. Therefore, colloidal particles have a certain charge, such as silicon iron aluminum compounds, some high molecular organics such as humus, and some bacteria and viruses within this particle size range

the third category is solutes, solutes or gases in molecular or ionic state that are only dissolved by water, such as chloride, sulfate, etc

suspended solids and colloids are the main causes of turbidity in natural water

4. Pretreatment of raw water

reverse osmosis has certain requirements for influent water quality due to the relationship between membrane materials and components. The problems to be solved by pretreatment are gambling, structure, pollution and wave damage. Blocking refers to the blocking of the flow channel of membrane components by particles, suspended solids, colloids and iron oxide deposits in the water. Scaling refers to the concentration and thick crystallization of insoluble salts on the concentrated water side, which can be removed or added with scale inhibitor in advance. Pollution refers to the adsorption of oil and organic matter on the surface of the membrane, microbial reproduction, colloid adsorption, etc., which are solved by sterilization, oxidative damage, flocculation filtration, activated carbon adsorption, etc. wave damage refers to the destruction of membrane materials by free poplar, ozone and other oxidants, and the removal of organic matter by activated carbon adsorption or adding reductant

1. The traditional pretreatment method

multi-media filter mainly depends on flocculation, It is only effective for granular or colloidal macromolecular substances, but not for dissolved natural organic substances and many industrial organic pollutants.

activated carbon adsorption can partially remove small molecule organic substances through adsorption, and the removal rate of COD by activated carbon is%. Activated carbon is not used for filtration

2. Membrane pretreatment

membrane pretreatment provides a reliable guarantee of inlet water quality for the downstream delay system

filtration is a membrane separation process based on the separation principle of screening and driven by pressure potential. The two cylindricity of 40mm long filter are in the range of 0.005um-0.01um, which can effectively remove particles, colloids, bacteria and macromolecular organics in water. The ultrafiltration process has no phase transformation, and has good temperature resistance, acid-base resistance and oxidation resistance. Ultrafiltration adopts membrane materials with different molecular weight and process design, which can adapt to different water quality conditions and separation functions

5. Reverse osmosis

reverse osmosis is abbreviated as RO, which is mainly composed of high-pressure pump and reverse osmosis membrane. Under high pressure, water molecules are removed and other substances, minerals, hip-hop, microorganisms, etc. in the water, which are impacted by high-pressure water flow and permeated to the other side, even if it is safe, sanitary and pure water. The separation characteristics of reverse osmosis can be used to effectively remove dissolved salts, colloids, organics, bacteria, etc. reverse osmosis has the advantages of low energy consumption, no pollution, process traps, simple operation, etc. reverse osmosis technology can be used for softening and desalting of filtered make-up water, desalination of sea water and brackish water, preparation of purified drinking water, preparation of ultra pure water in electronic industry, separation, concentration and recovery in tiger's den and food industry, And other process water

influencing factors of reverse osmosis membrane

1. Recovery rate: too high recovery rate will cause membrane pollution or excessive dissolved salt precipitation in concentrated water, which leads to membrane scaling caused by the main supplier of modified nylon for high-speed rail in China

2. Temperature: temperature has an effect on osmotic pressure and water flux. Water flux is directly proportional to temperature, usually directly proportional to the viscosity of temperature change. Generally, the water temperature increases by one degree, and the membrane water yield increases by 3%

3. Pressure: for a given set of influent conditions, increasing the pressure will increase the water flow per unit membrane area. Although the salt flux is not affected by the pressure, the increase of water flow caused by increasing the pressure dilutes the passage of salt to the membrane, resulting in the decrease of the salt concentration of the permeate

6. EDI technology

edi is characterized by the integration of electrodialysis technology and ion exchange technology, which can continuously produce high-quality pure water without acid and alkali, and use electricity instead of acid and alkali to regenerate the resin. In short, Dei is a new technology for producing pure water without consuming acid and alkali, commonly known as electrodialysis of mixed bed and packed bed. Dei can continuously produce and continuously regenerate, with stable water quality, low operation cost and convenient operation and management, It has the advantages of small floor area, no waste water and chemical pollution discharge, which is conducive to water saving and environmental protection, and also saves sewage treatment investment and water treatment cost

7. Conclusion

a desalination system without acid and alkali is formed by using the membrane process composed of ultrafiltration, reverse osmosis, EDI and other membrane elements. The ultrafiltration system, as a pretreatment, realizes the efficient and safe operation of the reverse osmosis system. The reverse osmosis membrane with high desalination rate is used for treatment. The quality of reverse osmosis produced water in the century meets the inflow standard of EDI. The modular design of EDI membrane element can facilitate the combination of any water production scale, completely avoid acid and alkali, reduce the floor space, and apply to the desalination system for various purposes, which has raised the development of water treatment technology to a new height

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