10 common water treatment methods
2021-02-05 12:20:53
1. Precipitation filtration method This is the most primitive filtration method. It relies on the self-weight sinking of particulate impurities in water to achieve separation. It is often used in places with large impurity particles in water, such as the initial Natural clarification filtration of rivers and lakes.
2. Distillation distillation is a method in which water is heated to become a gas, and a low-boiling component or a droplet component mixed in the gas phase is separated, and a low-boiling gas is placed in the atmosphere. The non-volatile impurities remain in the liquid phase and are discharged as a concentrate. The water is thus refined into high purity water.
This method consumes a lot of power and is used by some people when it is used. It is inconvenient to use and is rarely used.
3. Thin film microfiltration (MF) method The membrane micropore filtration method includes three forms: deep filtration, sieve filtration, and surface filtration.
Deep filtration is a matrix made of woven fiber or compressed material, which is retained by smear adsorption or capture, such as common multi-media filtration or sand filtration; deep filtration is a more economical way to remove 98 More than % of the suspended solids, while protecting the downstream purification unit from clogging, is usually used as a pretreatment.
The surface filtration is a multi-layer structure. When the solution passes through the membrane, particles larger than the pores inside the membrane will be left behind and mainly deposited on the surface of the membrane, such as the commonly used PP fiber filtration. Surface filtration removes more than 99.9% of suspended solids, so it can also be used as a pretreatment or clarification.
The mesh membrane is basically a uniform structure, like a sieve, leaving particles larger than the pore size on the surface (the pore size of this membrane is very accurate), such as the use of ultrapure water machine terminals. A point security filter; screen filtration microfiltration is typically placed at the end point of use in the purification system to remove the last remaining traces of resin tablets, carbon chips, colloids, and microorganisms.
4. Activated carbon adsorption method Activated carbon relies on adsorption and filtration to remove organic impurities such as color, odor, residual chlorine and residual disinfectants.
5. Electrodialysis dialysis is a physical phenomenon. For example, two different concentrations of brine are separated by a permeable membrane, and the solute such as inorganic salt ions in the high concentration brine is permeated through the membrane into the low concentration brine, which is dialysis. This dialysis is caused by the difference in the concentration of the salt, which is called concentration dialysis. Because the concentration difference is used as the driving force, the diffusion speed is always slow. If you want to speed up this speed, you can add a DC electrode on both sides of the membrane. Electrolytes, under the action of an electric field, accelerate the rate of migration, which is called electrodialysis.
Electrodialysis consumes a large amount of electricity, and the dialysis membrane is fragile, and has rarely been used after the emergence of reverse osmosis technology.
6. The principle of ion exchange (IX) ion exchange method is to exchange inorganic salt anion cations such as calcium ion Ca2+, magnesium ion Mg2+, sulfate SO42-, nitrate NO3-, etc. in raw water* with ion exchange resin. The anion and cation in the water are exchanged with the anion and cation in the resin to soften or purify the water.
Note 1: Raw water means that the water is called raw water relative to each filter unit.
Ion exchange resin* is divided into anionic resin (R-OH) and cationic resin (HR and Na-R), wherein the cationic resin is classified into sodium type resin (Na-R) and hydrogen type according to different reactive groups. Resin (HR). Sodium type resin is often used for water softening. Hydrogen type resin is often used together with anionic resin R-OH to remove inorganic salts and anions from water, and purify the water into ultrapure water.
Note 2: The ion exchange resin means that the polymer group of the ion exchange resin is usually represented by R.
Purification process:
For example, if HR stands for hydrogen-type cation resin, the exchange process of purified water quality is as follows:
2H-R+Ca2+ = R2Ca + 2H+
2R-OH+ SO42- = R2SO4 + 2OH-
The H+ and OH- generated in the above process are re-reacted:
H+ + OH- = H2O
That is, after the water is passed through the ion exchanger, the inorganic salt anion and cation in the water are replaced by H2O for purification purposes.
Softening process:
For example, Na-R represents a sodium type resin, and the exchange process is as follows:
2Na-R+Ca2+=R2Ca+2Na+
2Na-R+Mg2+=R2Mg+2Na+
That is, after the water is passed through the sodium ion exchanger, Ca2+ and Mg2+ in the water are replaced by Na+ to achieve the purpose of softening.
Regeneration process:
After the ion exchange resin is used for a period of time, the ions in the resin are completely exchanged, the saturation level is reached, and the ion exchange capacity is lost. At this time, the resin needs to be regenerated.
Softening the resin requires regeneration with a NaCl salt solution, and the chemical reaction during the regeneration process is exactly the opposite of the ion exchange reaction of the softening process described above.
The cation resin for purifying water needs to be regenerated with an acid, and the anion resin needs to be regenerated with a base. The chemical reaction of the regeneration process is exactly the opposite of the ion exchange reaction of the above purification process.
7. The ultrafiltration (UF) microporous membrane removes particles according to the size of the filter pore size, while the ultrafiltration (UF) membrane acts like a molecular sieve, which allows the solution to pass through the very fine pores to achieve the separation solution. The purpose of molecules of different sizes.
Ultrafiltration membrane is a tough, thin, selective membrane that is generally considered to have a filtration pore size of about 0.01 μm and can retain molecules of a certain size or above, including: colloids, microorganisms, and heat sources. Smaller molecules, such as water and ions, can pass through the filter.
Ultrafiltration is commonly used for juice concentration, Chinese herbal medicine extraction, reverse osmosis pretreatment, and ultra-pure water terminal security filtration.
8. Reverse osmosis (RO) method is a high-tech membrane separation technology. It is a separation process of pure water extracted from a water body containing various inorganic substances, organic substances and microorganisms by using pressure as a driving force and utilizing the reverse osmosis membrane to permeate only water and not to pass the solute. The reverse osmosis membrane has a pore diameter of less than 10 angstroms (1 angstrom is equal to 10-10 meters) and has a strong sieving effect, the salt rejection rate is as high as 99%, and the sterilization rate is greater than 99.5%. It can remove inorganic salts, sugars, amino acids, bacteria, viruses and other impurities in water. It has been widely used in the desalination treatment of seawater, the production of purified water, the preparation of ultrapure water, and other advanced processes for the removal of bacteria, pyrogens, colloids, particles and organic matter.
Based on raw water quality and water quality, RO is the most economical and effective method for purifying tap water. It is also the best pretreatment method for ultrapure water system.
9. Ultraviolet (UV), ozone sterilization UV light emitted by 254nm ultraviolet light is an effective sterilization method, because DNA and protein in bacteria will absorb ultraviolet rays and cause death.
UV sterilization method Ozone sterilization method: ozone generator is used to generate ozone, added to pure water, and the sterilization effect is excellent.
10. EDI method A new method of deionized water treatment. Also known as continuous electric desalination technology, an EDI device encloses an ion exchange resin between an anion/cation exchange membrane to form an EDI unit. This method does not need to regenerate the resin with acid and alkali, and has good environmental protection. Now widely used
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