What are the water treatment methods

Commonly used water treatment methods are: (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 (9) Biochemical method, etc.,

 Sediment filtration method The purpose of the sediment filtration method is to remove suspended particulate matter or colloidal matter from the water source. If these particulate matter is not removed, it will damage the other delicate filter membranes of the 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, or if necessary, several more filters are 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. The ions dissolved in the water cannot be blocked. If the filter is not replaced or cleaned for too long, 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 clogging of the filter. Therefore, the filter should be backwashed regularly to remove impurities accumulated on it, and the filter should be replaced within a fixed time. There is also a problem with the sediment filtration method that is worth noting. Because particulate matter is constantly blocked and accumulated, bacteria may multiply here and release toxic substances through the filter, causing pyrogen reaction. Therefore, the filter should be replaced frequently. Principle When the pressure drop between the upper inlet and outlet water rises five times the original, the filter needs to be replaced.

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,* to reduce the concentration of calcium and magnesium ions in the water source. The softening reaction formula is as follows: Ca2++2Na-EX→Ca-EX2+2Na+1 Mg2++2Na-EX→Mg-EX2+2Na+1 where EX stands for ion exchange resin, these ion exchange resins combine After Ca2+ and Mg2+, the Na+ ions originally contained in them are released. The ion exchange resins currently on the market are spherical synthetic organic polymer electrolytes. The resin matrix contains sodium chloride. In the process of hard water softening, the sodium ions will gradually be used up, and the softening effect of the exchange resin will gradually decrease. At this time, regeneration is required. That is, add brine of a specific concentration at regular intervals, usually 10%, and the reaction method is as follows: Ca-EX2+2Na+ (concentrated brine) → 2Na-EX+Ca2+ Mg-EX2+2Na+ (concentrated brine) → 2Na-EX +Mg2+ If there is no cationic softening during the water treatment process, not only will calcium and magnesium bodies be deposited on the reverse osmosis membrane, which will reduce the efficiency or even destroy the reverse osmosis membrane, but the patient will also easily get hard water syndrome. Hard water softeners can also cause the problem of bacterial reproduction, so the equipment needs to have a backwash function. After a period of time, it must be backwashed once to prevent too much impurities from adsorbing on it. Another noteworthy problem is hypernatremia, because the softening and re-reduction process of dialysis water is controlled by a timer. Normally, the reduction effect mostly occurs in the middle of the night. This is because the valve is in control. If it fails, a lot of salt water It will flood into the water source and cause hypernatremia in the patient.

Activated carbon adsorption method. Activated carbon is carbonized by dry distillation of wood, wood chips, fruit cores, coconut shells, coal or petroleum bottom residue at high temperature, and it needs to be activated with hot air or water vapor. Its main function is to remove chlorine and chloramines and other dissolved organic substances with a molecular weight of 60 to 300 Daltons. The surface of activated carbon is granular and the inside is porous. There are many capillaries of about 10nm~1A in the pores. 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 is. The factors that affect the ability of activated carbon to remove organic matter include the area of activated carbon itself, the size of the pores, and the molecular weight and polarity of the removed organic matter (Polarity). It is mainly * physical adsorption capacity to exclude impurities. When the adsorption capacity reaches saturation, adsorption Excessive impurities will fall down and pollute the downstream water quality, so it is necessary to regularly use the method of thrust to remove the impurities adsorbed on it. If the adsorption capacity of this activated carbon filter decreases significantly, it must be replaced. Measuring the TOC concentration difference (or the difference in the number of bacteria) between the inlet and outlet water is one of the basis for considering the replacement of activated carbon. Some reverse osmosis membranes have poor tolerance to chlorine, so activated carbon must be treated before reverse osmosis, so that chlorine can be effectively adsorbed by the activated carbon, but the bacteria adsorbed by the holes on the activated carbon are easy to multiply and grow. The effect of activated carbon is limited for the removal of relatively large organic matter, so it must be reinforced with a reverse osmosis membrane.

Deionization method The purpose of the deionization method is to remove inorganic ions dissolved in water. Like the hard water softener, it also uses the principle of ion exchange resin. Two resins are used here-cation exchange resin and anion exchange resin. Cation exchange resins use hydrogen ions (H+) to exchange cations; while anion exchange resins use hydroxide ions (OH-) to exchange anions. Hydrogen ions and hydroxide ions combine to form neutral water. The reaction equation is as follows: M+x+xH-Re→MM-Rex+xH+1 A-z+zOH-Re→A-Rez+zOH-1 In the above formula, M+x means cation, x means electricity value, M+x cation Exchange with the hydrogen ion of H-Re on the cationic resin, Az represents the anion, z represents the valence number, after Az is combined with the anion exchange resin, OH- ions are released. The combination of H+ ions and OH- ions becomes neutral water. These resins also need to be reduced after their adsorption capacity is exhausted. Cation exchange resins need strong acids to reduce; on the contrary, anions need 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 with each anion is as follows: S02-4+>I->NO3->NO2->Cl->HCO3->OH->F- If the anion exchange resin is exhausted Without reduction, the weakest fluorine 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 the acidity of the water, so whether the deionization function is effective requires frequent monitoring. It is generally judged by the resistance coefficient (resistivity) or conductivity (conductivity) of the water quality. The ion exchange resin used in the deionization method can also cause bacteria to multiply and cause bacteremia, which is worth noting.

Reverse osmosis method Reverse osmosis method can effectively remove inorganic substances, organic substances, bacteria, pyrogens and other particles dissolved in water. It is the most important part of the treatment of dialysis water. To understand 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 semi-permeable membrane, where the solute cannot penetrate the semi-permeable membrane, and the lower concentration One side of the water molecules will pass through the semi-permeable membrane to reach the other with a higher concentration until the concentrations on both sides are equal. Before reaching the equilibrium, you can gradually apply pressure on the side with the higher concentration, and the aforementioned water molecule movement state will be Stop temporarily, the pressure required at this time is called "osmotic pressure". If the applied force is greater than the osmotic pressure, the water will move in the opposite direction, that is, from a high concentration to a low concentration. On the other side, this phenomenon is called "reverse osmosis." The purification effect of reverse osmosis can reach the level of ions, and the rejection rate for monovalent ions can reach 90%-98%, and Divalent ions can reach about 95%-99% (which can prevent substances with a molecular weight greater than 200 daltons from passing). The commonly used semi-permeable membrane materials for reverse osmosis water treatment include cellulosic, aromatic poly Aromatic polyamides, polyimide or polyfuranes, etc. As for its structural shapes, spiral wound, hollow fiber and tubular, etc. As for the advantages of cellulose membranes in these materials It is highly resistant to chlorine, 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 used It is better, but there is no final conclusion. If there is no pre-treatment before reverse osmosis, there will be dirt accumulation on the permeable membrane, such as calcium, magnesium, iron plasma, which will cause the decline of reverse osmosis; some membranes (such as polyamide) It is easily destroyed by chlorine and chloramines, so it is necessary to have activated carbon and softener before the reverse osmosis membrane. Although the price of reverse osmosis is higher, because the pore size of the general reverse osmosis membrane is about 10A or less, it can eliminate bacteria , Viruses, pyrogens, and even various soluble ions, so it is best to prepare this step when preparing the water for hemodialysis.