Water treatment is through physical and chemical means, to remove the water some of the production, life does not need the material process. In order to be suitable for specific purposes and water settlement, filtration, coagulation, flocculation, as well as corrosion inhibition, scale inhibition and other water quality conditioning process. Because social production, life and water are closely related, therefore, the field of water treatment involves a wide range of applications, constituting a huge industrial applications. Often said water treatment equipment includes: sewage treatment and drinking water treatment of two kinds. Often used water treatment chemicals are: polymerized aluminum chloride, polymerized aluminum chloride iron, alkaline aluminum chloride, polyacrylamide, activated carbon and a variety of filter media. Commonly used water treatment methods are: (a) sediment filtration, (b) hard water softening, (c) activated carbon adsorption, (d) deionization, (e) reverse osmosis, (f) over-filtration, (g) distillation, (h) ultraviolet disinfection, and so on, and now the principle of these treatments and the function of the method is explained here.
A, sediment filtration method
Sediment filtration method is the purpose of the water source of suspended particulate matter or colloidal material to remove the clean. These particles, if not removed, will cause damage to the dialysis water and other delicate filter membrane or even blockage of the waterway. This is the oldest and simplest method of water purification, so it is often used in the initial stages of water purification or, if necessary, a few additional filters are added to the piping to remove larger contaminants. There are many types of filters used to filter floating particulate matter, such as mesh filters, sand filters (e.g., quartz sand, etc.) or membrane filters, etc. As long as the size of the particles is greater than the size of the holes in the filter, it is possible to remove the particles from the filter. As long as the size of the particles is larger than the size of the holes, they will be blocked. Ions dissolved in water cannot be blocked. If the filter is not changed or cleaned for a long time, more and more particles will accumulate on the filter, and the water flow rate and water pressure will gradually decrease. People use the difference between the inlet pressure and outlet pressure to determine the degree of blockage of the filter. Therefore, the filter should be backflushed regularly to remove the impurities that have accumulated on it, and the filter should be replaced at regular intervals. Sediment filtration method is also worth noting that there is a problem, because the particulate matter is constantly blocked and build up, the surface of these substances may be bacteria in the breeding, and release toxic substances through the filter, resulting in pyrogenic reactions, so it is necessary to change the filter often, in principle, the water inlet and outlet water pressure difference rises to five times the original, it is necessary to change out of the filter.
Two, hard water softening method
Softening of hard water needs to use ion exchange method, its purpose is to use cation exchange resin to sodium ions to exchange hard water calcium and magnesium ions, * this to reduce the concentration of calcium and magnesium ions within the water source. The softening reaction formula is as follows: Ca2++2Na-EX→Ca-EX2+2Na+1Mg2+++2Na-EX→Mg-EX2+2Na+1The EX in the formula indicates the ion-exchange resins, which release the Na+ ions that were originally contained in the ion-exchange resins after combining Ca2+ and Mg2+.
The ion exchange resins available on the market today are spherical, synthetic organic polymer electrolytes. The resin matrix (resin matrix) contains sodium chloride, in the process of hard water softening, sodium ions will gradually be used up, the softening effect of the exchange resin will gradually reduce, then need to do the work of reduction (regeneration), that is, every fixed period of time to add a specific concentration of brine, generally 10% of the reaction is as follows: Ca-EX2+ (concentrated salt water) 2Na+ (concentrated brine) → 2Na-EX+Ca2+Mg-EX2+2Na+ (concentrated brine) → 2Na-EX+Mg2+If there is no cation softening in the process of water treatment, not only will there be calcium and magnesium deposits on the reverse osmosis membrane, thereby reducing the efficacy of the reverse osmosis membrane or even destroying the reverse osmosis membrane, and at the same time, patients will be susceptible to the hard water syndrome. Hard water softeners can also cause bacterial growth problems, so the equipment needs to have a backwash function, after a period of time should be backwashed to prevent too many impurities adsorbed on it. Another problem that deserves attention is hypernatremia, because the softening and reduction process of dialysis water is controlled by a timer. Under normal circumstances, most of the reduction occurs in the middle of the night, and this is controlled by a valve, so if there is a malfunction, a large amount of brine will pour into the water supply, which will cause hypernatremia in the patient.
Three, activated carbon
Activated carbon is made of wood, wood chips, fruit kernels, coconut shells, coal or petroleum residue and other substances at high temperatures in the dry distillation of carbonization, made after the need for hot air or water vapor to activate. Its main function is to remove chlorine and chlorine-ammonia as well as other dissolved organic substances with a molecular weight of 60 to 300 daltons. The surface of activated carbon is granular, the interior is porous, and there are many capillary tubes of about 1Onm~lA size in the pores. 1g of activated carbon has an internal surface area as high as 700-1400m2, and the internal surface of these capillary tubes and the surface of the particles is where the adsorption is. Factors affecting the ability of activated carbon to remove organic matter are the area of the activated carbon itself, the size of the pore and the molecular weight of the organic matter to be removed and its polarity (Polarity), which is mainly * physical adsorption capacity to exclude debris, when the adsorption capacity up to the saturation of the adsorption of excessive impurities will fall down to contaminate the downstream of the water, so it must be timed to use the backwash to remove the impurities adsorbed on the way. If the adsorption capacity of this activated carbon filter decreases significantly, it must be renewed. Measuring the difference in TOC concentration (or bacterial count) between the influent and effluent is one of the bases for considering the replacement of activated carbon. Some reverse osmosis membrane chlorine tolerance is not good, so before reverse osmosis to have active carbon treatment, so that chlorine can be effectively adsorbed by the activated carbon, but the pores on the activated carbon adsorption of bacteria are easy to reproduce and grow, at the same time for the removal of molecules of larger organic matter, the activated carbon is limited in efficacy, so it must be * reverse osmosis membrane in the back of the reinforcement.
Four, deionization method
Deionization method aims to dissolve inorganic ions in the water to exclude the same as hard water softeners, but also the use of the principle of ion exchange resins. There are two types of resins used - cation exchange resins and anion exchange resins. The cation exchange resin utilizes hydrogen ions (H+) to exchange cations; while the anion exchange resin utilizes hydroxide ions (OH-) to exchange anions, and the hydrogen ions and hydroxide ions combine with each other to form neutral water, and 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 equation, M+x+x is cation and x is valence. In the above formula, M+x is the cation, x is the valence, M+x cation exchanges with the hydrogen ion of H-Re on the cation resin, A-z is the anion, z is the valence, and A-z releases OH- ions when it combines with the anion exchange resin, and the H+ ions combine with the OH- ions to form neutral water.
The adsorption capacity of these resins need to be restored after depletion. Cation exchange resins need strong acid to be restored; on the contrary, anions need strong alkaline to be restored. The adsorption capacity of cation exchange resin for various cations is different, and their strength and relative relationship are as follows: Ba2+>Pb2+>Sr2+>Ca2+>Ni2+>Cd2+>CU2+>Co2+>Zn2+>Mg2+>Ag1+>Cs1+>K1+>K1+>K1+>K1+>K1+>K1+>K1+>K1+>K1+>K1+>Cs1+> gt;K1+>NH41+>Na1+>H1+The strength of affinity between the anion exchange resin and each anion is as follows:S02-4+>I->NO3->NO2->Cl->HCO3->OH->F-If the anion exchange resin is consumed without reduction, the If the anion exchange resin is consumed without reduction, fluorine, which has the weakest adsorption, will gradually appear in the dialysis water, resulting in chondropathy, osteoporosis and other bone diseases; if the cation exchange resin is consumed, hydrogen ions will also appear in the dialysis water, resulting in an increase in the acidity of the water, so whether the deionization function is effective or not, it is necessary to monitor it from time to time. Therefore, the effectiveness of the deionization function requires constant monitoring. Generally, it is judged by the resistivity or conductivity of the water. The ion exchange resin used in the deionization method can also cause bacteria to multiply and cause bacteremia, which is worth noting.
Fifth, reverse osmosis
Reverse osmosis can effectively remove inorganic substances dissolved in the water, organic matter, bacteria, pyrogens and other particles, is the most important part of the treatment of dialysis water. To understand the principle of reverse osmosis, we should first explain the concept of osmosis. The so-called osmosis refers to a semi-permeable membrane separating two different concentrations of solution, in which the solutes can not pass through the semi-permeable membrane, the lower concentration of water molecules will pass through the semi-permeable membrane to reach the higher concentration of the other side, until both sides of the concentration of the two sides are equal. Before equilibrium is reached, the concentration of the higher side of the gradual application of pressure, the aforementioned water molecules will temporarily stop the state of movement, the pressure required at this time is called "osmotic pressure (osmotic pressure)", if the force applied to the osmotic pressure is greater than that of the movement of water will be in the opposite direction, that is, from the high concentration of a case of flow to the other side of the membrane, the water molecules will pass through the semi-permeable membrane to the other side of the higher concentration. If the force applied is greater than the osmotic pressure, the water will move in the opposite direction, i.e., from a high concentration to a low concentration, a phenomenon called "reverse osmosis". The purification effect of reverse osmosis can reach the level of ions, for monovalent ions (monovalent ions) exclusion rate (rejection rate) up to 90%-98%, and bivalent ions (divalent ions) up to 95%-99% or so (molecular weight of the material can be prevented from passing through the more than 200 daltons). Reverse osmosis water treatment commonly used semi-permeable membrane materials are fiber membrane (cellulosic), aromatic polycellulose amines (aromatic polyamides), polyimide or polyfuranes, etc., as for the structure of the shape of the spiral (spiral wound), hollow fiber (hollow fiber) and tubular (tubular). As for its structural shape, there are spiral wound, hollow fiber and tubular. Among these materials, cellulose membrane has the advantage of high chlorine resistance, but its service life will be shortened under alkaline conditions (pH ≥ 8.0) or the presence of bacteria, while polyamide has the disadvantage of poor resistance to chlorine and chloramines. No conclusions have been reached as to which material is preferred. If the reverse osmosis is not properly pre-treatment before the permeate membrane is prone to dirt accumulation, such as calcium, magnesium, iron and other ions, resulting in the decline of reverse osmosis function; some membranes (e.g., polyamide) are easy to be destroyed by chlorine and chlorine ammonia, so before the reverse osmosis membrane should be activated carbon and softeners and other pre-treatment. Although the price of reverse osmosis is higher, because the pore size of reverse osmosis membrane is below l0A, it can exclude bacteria, viruses and pyrogens, and even a variety of dissolved ions, so it is best to prepare this step in the preparation of hemodialysis dialysis water.
Sixth, over filtration method
Over filtration method is similar to reverse osmosis method, also use semi-permeable membrane, but it can not control the removal of ions, because the pore size of the membrane is large, about 10-200A. It can only remove bacteria, viruses, pyrogens, and particulate matter, but not water-soluble ions. The main function of ultrafiltration is to act as a 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 the upstream water in the piping. Generally, it uses the difference between the inlet and outlet water pressure to determine whether the membrane is effective or not. Similar to activated carbon, it is usually used to remove the impurities attached to it by reverse osmosis method.
Seven, distillation method
Distillation method is an ancient but effective water treatment method, it can remove any non-volatile impurities, but can not exclude volatile pollutants, it requires a large water tank to store the water tank and pipeline is an important cause of contamination, hemodialysis water is not used to deal with this way.
Eight, ultraviolet disinfection method
Ultraviolet disinfection method is one of the commonly used methods, its sterilization mechanism is to destroy the bacterial nucleic acid life of the genetic material, so that it can not reproduce, the most important reaction is the nucleic acid molecules within the pyrimidine salt group into a double (dimer). The most important reaction is that the pyrimidine salt group in the nucleic acid molecule becomes a dimer. Generally, the artificial 253.7nm wavelength of ultraviolet energy is used in low-pressure mercury discharge lamps (germicidal lamps). The principle of UV germicidal lamps is the same as that of fluorescent lamps, except that the inside of the lamp is not coated with fluorescent material, and the material of the lamp is quartz glass with a high UV penetration rate. General ultraviolet device according to the use of irradiation, immersion type and water type. The ultraviolet germicidal lamps used in the dilution of water for hemodialysis are placed in the pipeline between the water tank and the dialysis machine, that is, all the dialysis water should be irradiated with ultraviolet rays before use, in order to achieve the effect of complete sterilization. The most sensitive to UV light are Pseudomonas aeruginosa and E. coli; on the other hand, the more tolerant are Bacillus subtilis. Because the ultraviolet disinfection method is safe, economical, less selective of bacteria, water quality will not change, so in recent years has been widely used in this way, such as the ship's drinking water is often used in this disinfection method. The water of Angora, Basella, Salmonella and so on all killed, can be submerged in the water center 360 degrees sterilization, efficacy is equal to the surface of the germicidal lamp of three times. Can eliminate the water Loc algae, the effect is remarkable, easy to use, ultraviolet germicidal lamps are suitable for: various sizes of fisheries filtration, water treatment, large and small pools, swimming pools, hot springs. Sterilization efficiency up to 99%-99.99%.
Nine, biochemical method
[1] Biochemical water treatment methods using nature survives a variety of bacterial microorganisms, the decomposition of wastewater organic matter into harmless substances, so that wastewater can be purified. Biochemical water treatment method can be divided into activated sludge method, biofilm method, biological oxidation tower, land treatment system, anaerobic biological water treatment method. The flow of biochemical water treatment method: raw water → grating → regulating pool → contact oxidation pool → sedimentation land → filtration → disinfection → effluent.
1, activated sludge water treatment method (1) drum aeration: that is, exhaust aeration, the compressed air is constantly drummed into the wastewater to ensure that there is a certain amount of dissolved oxygen in the water to maintain microbial life activities, decomposition of organic matter in the water, in order to achieve purification effect of water treatment. (2) mechanical aeration: that is, surface aeration, the use of mechanical impellers installed in the aeration tank rotating, stirring the water surface, so that the oxygen in the air dissolved in the water for microbial life activities, biochemical effects to achieve the purification effect of water treatment. (3) Oxygen aeration: it is according to the blower aeration method into the water blowing pure oxygen, in order to improve the oxygenation efficiency, so as to speed up the purification rate of water treatment.
2, biofilm water treatment methods (1) biofilter: so that the wastewater flows through the growth of biofilm on the surface of the filter media, through the exchange of substances between the two surfaces and biochemical effects, so that the degradation of organic matter in the wastewater to achieve the purification purpose of water treatment. (2) biological turntable: fixed on a horizontal axis of a number of closely spaced discs, constantly rotating disc surface growth of a layer of biofilm to achieve the purification effect of water treatment. (3) biological contact oxidation: for microorganisms attached to the filler all immersed in wastewater, and the use of mechanical equipment to the wastewater filled with air, so that the wastewater in the degradation of organic matter, in order to purify wastewater.
3, land treatment system (1) land infiltration: the use of microorganisms in the soil membrane and plant roots on the purification of pollutants to carry out domestic sewage treatment, while the use of sewage in the water, fertilizer to promote the growth of crops, pasture, trees. (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 methods: the use of anaerobic microorganisms to decompose organic matter in sewage, to achieve the purpose of water treatment and purification, and at the same time produce methane gas, CO2 and other gases.
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