Introduction to commonly used water treatment equipment treatment methods and functions
Water treatment is the process of removing some substances in the water that are not necessary for production and life through physical and chemical means. The process of water quality conditioning such as sedimentation, filtration, coagulation, flocculation, corrosion inhibition, and scale inhibition in order to suit specific purposes. Since social production and life are closely related to water, the field of water treatment involves a wide range of applications and constitutes a huge industrial application. Commonly mentioned water treatment equipment includes: sewage treatment and drinking water treatment. Commonly used water treatment chemicals include: polyaluminum chloride, polyaluminum ferric chloride, basic aluminum chloride, polyacrylamide, activated carbon and various filter materials. Commonly used water treatment methods include: (1) sediment filtration method, (2) hard water softening method, (3) activated carbon adsorption method, (4) deionization method, (5) reverse osmosis method, (6) ultrafiltration method, (7) Distillation method, (8) Ultraviolet disinfection method, etc. Now the principles and functions of these treatment methods are explained here one by one.
1. Sediment filtration method
The purpose of the sediment filtration method is to remove suspended particulate matter or colloidal matter in the water source. If these particulate matter is not removed, it will cause damage to other precision filter membranes of dialysis water or even block the waterway. This is the oldest and simplest water purification method, so this step is often used in the preliminary treatment of water purification. If necessary, several more filters will be added to the pipeline to remove larger impurities. There are many types of filters used to filter suspended particulate matter, such as mesh filters, sand filters (such as quartz sand, etc.) or membrane filters. As long as the particle size is larger than the size of these holes, it will be blocked. For ions dissolved in water, it cannot be blocked. If the filter has not been replaced or cleaned for a long time, more and more particulate matter will accumulate on the filter, and the water flow and water pressure will gradually decrease. People use the difference between the inlet water pressure and the outlet water pressure to judge the degree of blockage of the filter. Therefore, the filter must be backflushed regularly to remove impurities accumulated on it, and the filter must also be replaced within a fixed period of time. There is another problem worth noting with the sediment filtration method. Because particulate matter is constantly blocked and accumulated, bacteria may breed on these materials and release toxic substances through the filter, causing pyrogen reactions. Therefore, the filter must be replaced frequently. In principle When the pressure difference between the upper inlet and outlet water increases to five times the original value, the filter needs to be replaced.
2. Hard water softening method
The softening of hard water requires the use of ion exchange method. Its purpose is to use cation exchange resin to exchange calcium and magnesium ions in hard water with sodium ions.* This reduces the concentration of calcium and magnesium ions in the water source. The softening reaction formula is as follows: Ca2++2Na-EX→Ca-EX2+2Na+1Mg2++2Na-EX→Mg-EX2+2Na+1 EX in the formula represents ion exchange resin. These ion exchange resins combine Ca2+ After removing Mg2+, the Na+ ions originally contained in it are released.
The ion exchange resin currently on the market is a spherical synthetic organic polymer electrolyte. The resin matrix contains sodium chloride. During the hard water softening process, sodium ions will be gradually used up, and the softening effect of the exchange resin will gradually decrease. At this time, regeneration work is required. That is to say, a specific concentration of salt water is added at regular intervals, usually 10%. The reaction method is as follows: Ca-EX2+2Na+ (concentrated salt water) → 2Na-EX+Ca2+Mg-EX2+2Na+ (concentrated salt water) → 2Na- EX+Mg2+ If there is no softening of cations during the water treatment process, not only will calcium and magnesium be deposited on the reverse osmosis membrane, which will reduce the efficiency or even destroy the reverse osmosis membrane, but patients will also be prone to hard water syndrome. Hard water softeners can also cause bacterial growth problems, so the equipment needs to have a backflush function. It must be backflushed after a period of time to prevent too many impurities from adsorbing on it. Another issue worth noting is hypernatremia, because the softening and re-reduction process of dialysis water is controlled by a timer. Under normal circumstances, the reduction occurs mostly in the middle of the night. This is controlled by the *valve. If a failure occurs, a large amount of saline water will be released. Water will flow into the water source, causing the patient's hypernatremia.
3. Activated carbon
Activated carbon is made by carbonization of wood, residual sawdust, fruit cores, coconut shells, coal or petroleum bottom residue at high temperatures. After completion, it needs to be activated with hot air or water vapor. Its main function is to remove chlorine, chlorine, ammonia and other dissolved organic substances with a molecular weight of 60 to 300 Daltons. The surface of activated carbon is granular, and the interior is porous. There are many capillaries in the pores with a size of about 1Onm~1A. The internal surface area of ??1g of activated carbon is as high as 700-1400m2, and the inner surface of these capillaries and the surface of the particles are where the adsorption occurs. Factors that affect the ability of activated carbon to remove organic matter include the area of ??the activated carbon itself, the size of the pores, the molecular weight of the organic matter to be removed, and its polarity (Polarity). It mainly relies on physical adsorption capacity to remove impurities. When the adsorption capacity reaches saturation, , excessive adsorbed impurities will fall down and pollute the water quality downstream, so backflushing must be used regularly to remove the adsorbed impurities. If the adsorption capacity of this activated carbon filter decreases significantly, it must be replaced. Measuring the TOC concentration difference (or bacterial count difference) between the incoming water and the outgoing water is one of the basis for considering replacing activated carbon. Some reverse osmosis membranes have poor tolerance to chlorine, so they must be treated with activated carbon before reverse osmosis so that chlorine can be effectively adsorbed by the activated carbon. However, bacteria adsorbed by the holes on the activated carbon are easy to multiply and grow. At the same time, for For the removal of organic matter with larger molecules, activated carbon has limited effectiveness, so a reverse osmosis membrane must be used to reinforce it behind.
IV. Deionization method
The purpose of the deionization method is to remove inorganic ions dissolved in the water. Like the hard water softener, it also uses the principle of ion exchange resin. Two types of resins are used here - cation exchange resin and anion exchange resin. Cation exchange resin uses hydrogen ions (H+) to exchange cations; while anion exchange resin uses hydroxide ions (OH-) to exchange anions. Hydrogen ions and hydroxyl ions combine with each other to form neutral water. The reaction equation is as follows: M+x+xH-Re→M-M-Rex+xH+1A-z+zOH-Re→A-Rez+zOH-1 In the above formula, M+x represents the cation, x represents the electric valence, and the M+x cation and The hydrogen ion exchange of H-Re on the cation resin, A-z represents the anion, z represents the electric valence. After A-z combines with the anion exchange resin, OH- ions are released. H+ ions and OH- ions combine to form neutral water.
These resins also need to be reduced after their adsorption capacity is exhausted. Cation exchange resins require strong acids to reduce; conversely, anions require strong alkalis to reduce. Cation exchange resins have different adsorption capacities for various cations. Their strength and relative relationship are as follows: Ba2+>Pb2+>Sr2+>Ca2+>Ni2+>Cd2+>CU2+>Co2+>Zn2+>Mg2+>Ag1+>Cs1+>K1+> The affinity strength of NH41+>Na1+>H1+ anion exchange resin and each anion is as follows: S02-4+>I->NO3->NO2->Cl->HCO3->OH->F-If the anion exchange resin is exhausted and Without reduction, fluorine with the weakest adsorption force will gradually appear in the dialysis water, causing rickets, osteoporosis and other bone diseases; if the cation exchange resin is exhausted, hydrogen ions will also appear in the dialysis water. , resulting in an increase in water acidity, so whether the deionization function is effective requires constant monitoring. Generally, it is judged by the resistivity or conductivity of water quality. The ion exchange resin used in the deionization method can also cause bacterial reproduction and cause bacteremia, which is worth noting.
5. Reverse osmosis method
Reverse osmosis method can effectively remove inorganic substances, organic substances, bacteria, pyrogens and other particles dissolved in water. It is an important part of the treatment of dialysis water. The most important part. Before understanding the principle of "reverse osmosis", we must first explain the concept of "osmosis".
The so-called osmosis refers to the separation of two solutions of different concentrations by a semipermeable membrane. The solute cannot pass through the semipermeable membrane, so the water molecules on the side with a lower concentration will pass through the semipermeable membrane to the other side with a higher concentration. until the concentrations are equal. Before reaching equilibrium, you can gradually apply pressure on the side with higher concentration, and the aforementioned moving state of water molecules will temporarily stop. The pressure required at this time is called "osmotic pressure". If the force applied When the osmotic pressure is greater than the osmotic pressure, the movement of water will go in the opposite direction, that is, from the high concentration side to the low concentration side. This phenomenon is called "reverse osmosis". The purification effect of reverse osmosis can reach the ion level. The rejection rate of monovalent ions can reach 90%-98%, while the rejection rate of divalent ions can reach 95%-99%. About (can prevent substances with a molecular weight greater than 200 daltons from passing through). Commonly used semipermeable membrane materials for reverse osmosis water treatment include cellulosic membrane, aromatic polyamides, polyimide or polyfuranes, etc. As for its structural shape, there are spiral wound and hollow fiber type. (hollow fiber) and tubular type (tubular), etc. As for the advantage of cellulose membrane among these materials, it has high chlorine resistance, but under alkaline conditions (pH ≥8.0) or in the presence of bacteria, the service life will be shortened. The disadvantage of polyamide is its poor tolerance to chlorine and chloramine. As for which material is better, there is no conclusion yet. If pretreatment is not done before reverse osmosis, dirt will easily accumulate on the permeable membrane, such as calcium, magnesium, iron, etc., resulting in a decline in reverse osmosis function; some membranes (such as polyamide) are easily damaged by chlorine and chlorine ammonia. Therefore, there must be pre-treatment such as activated carbon and softener before the reverse osmosis membrane. Although reverse osmosis is more expensive, because the pore size of the general reverse osmosis membrane is about 10A or less, it can eliminate bacteria, viruses, pyrogens and even various dissolved ions, so it is best to prepare this step when preparing hemodialysis water. .
6. Ultrafiltration method
Ultrafiltration method is similar to reverse osmosis method. It also uses a semipermeable membrane, but it cannot control the removal of ions because the pore size of the membrane is larger, about Between 10-200A. It can only exclude bacteria, viruses, pyrogens and particulate matter, but cannot filter water-soluble ions. The main function of ultrafiltration is to act as pre-treatment for reverse osmosis to prevent the reverse osmosis membrane from being contaminated by bacteria. It can also be used in the final step of water treatment to prevent bacterial contamination of upstream water in the pipeline. Generally, the difference between the inlet water pressure and the outlet water pressure is used to judge whether the ultrafiltration membrane is effective. Similar to activated carbon, the backwash method is usually used to remove impurities attached to it.
7. Distillation
Distillation is an ancient but effective water treatment method. It can remove any non-volatile impurities, but it cannot eliminate volatile pollutants. It requires a large storage tank to store it. This storage tank and delivery pipe are important causes of pollution. Currently, hemodialysis water is not treated in this way.
8. Ultraviolet Disinfection Method
Ultraviolet disinfection method is one of the commonly used methods at present. Its sterilization mechanism is to destroy the genetic material of bacterial nucleic acid, making it impossible to reproduce. Among them, The most significant reaction is the transformation of the pyrimidine base within the nucleic acid molecule into a dimer. Generally, artificial 253.7nm wavelength ultraviolet energy is used from a low-pressure mercury discharge lamp (sterilizing lamp). The principle of ultraviolet germicidal lamps is the same as that of fluorescent lamps, except that the inside of the lamp tube is not coated with fluorescent substances. The material of the lamp tube is quartz glass with high ultraviolet transmittance. Generally, UV devices are divided into irradiation type, immersion type and flow type according to their uses. The ultraviolet rays used by water treatment ultraviolet germicidal lamps to dilute hemodialysis water are placed on the pipeline between the water storage tank and the dialysis machine. That is, all dialysis water must be irradiated with ultraviolet rays before use to achieve complete sterilization. Effect. The most sensitive ones to ultraviolet rays are Pseudomonas aeruginosa and Escherichia coli; on the contrary, the ones that are more tolerant are Bacillus subtilis spores.
Because the ultraviolet disinfection method is safe, economical, less selective for bacterial species, and the water quality will not change, this method has been widely used in recent years. For example, this disinfection method is often used for drinking water on ships. It can kill all Egola, Basella, Salmonella, etc. in the water. It can dive into the center of the water for 360-degree sterilization, and its efficacy is three times that of surface germicidal lamps. It can eliminate algae in water, has significant effect and is easy to use. Ultraviolet germicidal lamp is suitable for: filtration of various sizes of fishing grounds, water treatment, large and small pools, swimming pools, and hot springs. The sterilization efficiency can reach 99%-99.99%.
9. Biochemical method
[1] Biochemical water treatment method uses various bacterial microorganisms existing in nature to decompose and convert organic matter in wastewater into harmless substances, making the wastewater be purified. Biochemical water treatment methods can be divided into activated sludge methods, biofilm methods, biological oxidation towers, land treatment systems, and anaerobic biological water treatment methods. The process of biochemical water treatment method: raw water→grill→regulating tank→contact oxidation tank→sedimentation ground→filtration→disinfection→water outlet.
1. Activated sludge water treatment method (1) Blast aeration: that is, drainage aeration, which continuously blows compressed air into the wastewater to ensure that there is a certain amount of dissolved oxygen in the water to maintain The life activities of microorganisms decompose organic matter in the water to achieve the purification effect of water treatment. (2) Mechanical aeration: that is, surface aeration, which uses a mechanical impeller installed in the aeration tank to rotate and violently stir the water surface, so that oxygen in the air dissolves in the water, allowing microorganisms to move and perform biochemical effects to achieve the purification of water treatment. Effect. (3) Pure oxygen aeration: It blows pure oxygen into the water according to the blast aeration method to improve the oxygenation efficiency and thereby speed up the purification speed of water treatment.
2. Biofilm water treatment method (1) Biological filter: The wastewater flows through the biofilm growing on the surface of the filter material, and the organic matter in the wastewater is degraded through material exchange and biochemical effects between the two sides. Achieve the purification purpose of water treatment. (2) Biological turntable: It consists of several closely spaced discs fixed on a horizontal axis. A layer of biofilm grows on the surface of the constantly rotating discs to achieve water treatment and purification effects. (3) Biological contact oxidation: All the fillers for microorganisms to inhabit are immersed in the wastewater, and mechanical equipment is used to fill the wastewater with air to degrade the organic matter in the wastewater to purify the wastewater.
3. Land treatment system (1) Land infiltration: Use the ability of microorganisms and plant roots in the soil film to purify pollutants to treat domestic sewage, and use the water and fertilizer in the sewage to promote Crops, pasture, and trees grow. (2) Sewage irrigation: The main purpose of this water treatment method is irrigation to make full use of the purified sewage.
4. Anaerobic biological water treatment method: Use anaerobic microorganisms to decompose organic matter in sewage to achieve the purpose of water treatment and purification, and at the same time produce methane, CO2 and other gases.
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