What are the disinfectants commonly used in microbial limit check

Microbiological limit checks commonly used disinfectants which

According to research, can contaminate drinking water pathogenic microorganisms have hundreds of species, in order to prevent the occurrence of waterborne infectious diseases and epidemics, to ensure human health, drinking water must be disinfected for drinking. At present, China's drinking water disinfection methods mainly used for chlorination, chlorine dioxide disinfection, ultraviolet disinfection and ozone disinfection. Chlorination disinfection 1.1 commonly used types of chlorine disinfectant 1.1 Chlorine Molecular Formula for Cl2, molecular weight is 70.91. Chlorine is a strong oxidizing substance, at room temperature and pressure is a yellowish-green gas, chlorine gas is heavier than the air 2.5 times, with a strong irritating and chlorine odor. When pressurized to 6-7 atmospheric pressure can be liquefied, the volume is reduced by 457 times, can be poured into a cylinder for storage, it is also known as liquid chlorine. Liquid chlorine is 1.5 times heavier than water, liquid chlorine in the atmosphere, immediately become gas, chlorine gas into the water can be chlorine water. Chlorine added to water can be changed into hydrochloric acid and hypochlorous acid. 1.2 Bleaching powder Bleaching powder is also called chlorinated lime and chlorinated lime. It is a mixture made by passing chlorine gas into slaked lime, the main component is calcium hypochlorite (32%-36%), and also contains calcium chloride (29%), calcium oxide (10%-18%), calcium hydroxide (15%) and water (10%), and Ca0Cl2 is usually used to represent its molecular formula. Bleaching powder is a white granular powder with a chlorine odor, soluble in water, alkaline solution, and a large amount of sediment. Bleaching powder stability is poor, in the general preservation process, the effective chlorine can be reduced by 1-3% per month, so it is not advisable to save too long. 1.3 Bleaching powder will be chlorinated lime milk after crystallization and separation, and then dissolved in spray drying that is made of bleaching powder, bleaching powder containing calcium hypochlorite about 80%, also contains a small amount of calcium chloride (2.74%), calcium hydroxide (1.9%). Bleaching powder is a white powder, chlorine odor, soluble in water, alkaline solution, with a small amount of slag, stability is better than bleach, the effective chlorine content is double that of bleach. 1.4 Organic chlorine disinfectant Currently the most commonly used in a variety of items disinfection is sodium dichloroisocyanurate (euclid), sodium dichloroisocyanurate is a white powder, chlorine odor, chlorine content of 60% -64%, stable, soluble in water, the solution is weakly acidic. However, according to the study reported that the degree of toxicity of organic chlorine hazards than inorganic chlorine, and may have a carcinogenic effect, therefore, the use of organic chlorine disinfectant for long-term disinfection of drinking water is not appropriate. 1.5 Sodium hypochlorite Electrolysis of salt chlorine and sodium hydroxide generated sodium hypochlorite, molecular formula NaOCl, molecular weight of 74.44. Sodium hypochlorite is a light yellow liquid, chlorine odor, chlorine content of 12-14%, soluble in water, poor stability, heat and sunlight irradiation of the effective chlorine is easy to lose, so it is not suitable for long time to save. 2. The basic principle of chlorination disinfection 2.1 Chlorine sterilization mechanism Chlorine sterilization is due to hypochlorite small size, neutral charge, easy to pass through the cell wall; at the same time, it is a strong oxidizing agent that can damage the cell membrane, so that proteins, RNA and DNA and other substances released, and affects a variety of enzyme systems (mainly phosphoglucose dehydrogenase sulfhydryl group is oxidized and destroyed), thus causing the death of bacteria. The effect of chlorine on viruses lies in the lethal damage to nucleic acids. It has been pointed out that the resistance of viruses to chlorine is stronger than that of bacteria, which may be due to the lack of a series of viral metabolic enzymes; chlorine is easier to destroy the -SH bond, and it is more difficult to denature proteins. 2.2 Factors affecting the disinfection effect The effect of chlorination disinfection is affected by the following factors: the amount of chlorine, contact time, PH value, water temperature, water turbidity and the type and number of microorganisms. 2.2.1 Chlorination: Chlorine and chlorine-containing compounds to disinfect drinking water, chlorine not only with the role of bacteria in the water, but also oxidize the organic matter in the water and reducing inorganic substances, the total amount of chlorine needed is called "chlorine demand". In order to ensure the effect of disinfection, the amount of chlorine must exceed the chlorine demand of water, so that after the oxidation and sterilization can remain some effective chlorine, known as "residual chlorine". General requirements of chlorine added to the water, contact 30 minutes, the water should remain at least free residual chlorine 0.3mg / l. In the distribution network end, free residual chlorine should not be less than 0.05mg / l. Residual chlorine is divided into free residual chlorine and chemical residual chlorine two kinds of free HOCl, OCl- and Cl2; chemical compounds, such as NH2Cl and NHCl2. the former is more powerful bactericidal, the latter is weaker bactericidal. Weaker. 2.2.2 contact time: chlorine added to the water, must ensure that there is a certain contact time with the water, in order to give full play to the disinfection effect. With free chlorine (refers to HOCl and OCl-) disinfection, contact time should be at least 30 minutes, free residual chlorine up to 0.3-0.5mg / l; using chloramines (refers to NH2C1 and NHCl2) disinfection, contact time should be l-2 hours, the chemical residual chlorine up to 1-2mg / l. 2.2.2 Contact time: Chlorine added to the water must ensure that the water has a certain contact time to give full play to the role. -2.2.3 PH value of water: hypochlorite is a weak electrolyte, the degree of dissociation depends on the water temperature and water PH value. When the PH value <5.0, HOCL is 100% form in the water, with the increase of PH value, HOCl gradually reduce and OCL - gradually increased. PH value in 6.0, HOCl in more than 95%; PH value > 7.0 value, H0CL content is sharply reduced; PH = 7.5, HOCl and OCl - roughly equal; PH value > 9, OCl - close to 100%. 100%. According to the experiment on E. coli, the sterilization efficiency of hypochlorous acid (HOCl) is about 80 times higher than hypochlorite ion (OCL-). Therefore, disinfection should pay attention to control the pH value of the water, not too high, so as not to generate more OCl-, H0CL less and affect the sterilization efficiency. Disinfection with bleach, because at the same time produce Ca (OH) 2, can make the PH value rise. Therefore, when bleach is improperly preserved or placed for too long so that the effective chlorine content is low, the disinfection effect will be affected. The sterilization effect of dichloramine is higher than that of monochloramine, while trichloramine has almost no sterilization effect. The ratio between their production depends on factors such as the relative concentration of ammonia and chlorine, pH value and temperature. Generally speaking, when the PH value > 7, the generation of monochloramine is more; PH = 7.0, monochloramine and dichloramine are approximately equal; PH value <6.5, mainly dichloramine; trichloramine only when the PH value <4.4 exists. 2.2.4 Water temperature: high water temperature, good sterilization effect. Every 10 ℃ increase in water temperature, bacteria kill rate increased by about 2-3 times. 2.2.5 water turbidity: chlorine disinfection, must make the generation of hypochlorous acid (HOC1) and hypochlorite ions (OCl-) in direct contact with bacteria in the water, in order to achieve the sterilization effect. If the turbidity of the water is very high, more suspended substances, bacteria more attached to these suspended particles, the role of chlorine can not reach the bacteria themselves, so that the bactericidal effect is reduced. This shows the necessity of coagulation and precipitation and filtration treatment before disinfection. The effect of suspended particles on disinfection, depending on the nature of the particles, microbial species and different. Such as clay particles adsorption of microorganisms, the effect on the disinfection effect is very small, while the cellular debris in feces and urine, or organic particles in sewage and microorganisms combined, will make microorganisms to obtain significant protection. Virus due to small size, large surface area, easy to be adsorbed into a group, and thus the particles of viruses have a greater protective effect than bacteria. 2.2.6 Types and number of microorganisms in water Different microorganisms do not have the same tolerance to chlorine, except for adenovirus, enterovirus is more tolerant to chlorine than enteropathogenic bacteria. Disinfection is often less than 100% of the killing effect, often 99%, 99.9% or 99.99% of the effect as a parameter. Therefore, if too much bacteria in the water before disinfection, the number of bacteria in the water after disinfection is not easy to meet the requirements of health standards. 3. Chlorine disinfection of several methods 3.1 General chlorination disinfection When the water chlorine demand is low, and basically no ammonia (<0.3mg / L), add a small amount of chlorine to achieve the purpose of disinfection a disinfection method. This method produces mainly free residual chlorine, the required contact time is short, the effect is reliable; but the requirements of the source water is less polluted, and basically no phenolics (chlorine and phenol can be formed with the smell of chlorophenol); free residual chlorine is less stable, not easy to keep in the longer network to the end of the pipe network. 3.2 Folding point chlorine disinfection method using more than the folding point of the amount of chlorine, so that the formation of the right amount of free residual chlorine in the water, known as folding point chlorine disinfection method. The advantages of this method are: reliable disinfection; can significantly reduce manganese, iron, phenol and organic content; and has the effect of reducing odor and color. Disadvantages are more chlorine consumption, which may produce more chlorination by-products of trihalomethanes; need to find out in advance the amount of chlorine folding point, more trouble, and sometimes the water samples folding point is not obvious; will make the water PH value is too low, so it is necessary to add alkali adjustments to the fashion. 3.3 Chloramine disinfection method in the water by adding ammonia (liquid ammonia, sulfuric acid amine or amine chloride), the chlorine generated by a chloramine and dichloramine, this method for chloramine disinfection. The ratio of ammonia and chlorine should be determined by test, the range is generally 1:3-1:6. The advantages of this method are: the formation of trihalomethanes is significantly lower than ordinary chlorination; such as adding ammonia and then add chlorine, it can prevent chlorophenol odor, the chemical residual chlorine is more stable, can be maintained for a longer period of time in the pipeline network, so that the end of the network residual chlorine to be guaranteed. Disadvantages are: the disinfection effect of chloramine is not as strong as hypochlorite, the requirement to ensure a long enough contact time (2 hours) and a high residual chlorine (1-2mg / l), so the contact time is long, expensive; need to add ammonia and complex operation; the killing effect on the virus is poor. 3.4 excess chlorine disinfection When the water source by organic and bacterial contamination is more serious, or in the field work, marching and other conditions, the need to achieve disinfection in a short period of time, you can add excess chlorine in the water, so that the residual chlorine up to l-5mg / l. Disinfection of water need to be dechlorinated with sodium sulfite, sodium bisulfite, sodium thiosulfate) or activated carbon. 4.1 Chlorination and chlorination equipment 4.1 Chlorination in the water purification process, chlorination can be selected for the location of: 4.1.1 Chlorination before filtration refers to the coagulation and precipitation before the addition of chlorine, the main purpose is to improve the coagulation and precipitation and to prevent the growth of algae, but prone to generate a large number of chlorinated byproducts. 4.1.2 Chlorination after filtration means adding chlorine to the water after filtration, the purpose of which is to kill pathogenic microorganisms in the water, which is the most commonly used disinfection method. Can also take the second chlorination, that is, before coagulation and precipitation and filtration of each added once. 4.1.3 chlorination in the middle of the pipeline is long, in the middle of the network of pressurized pumping station or reservoir pumping station of the supplemental chlorine. The use of this method can ensure that the end of the residual chlorine, but does not lead to the water plant near the network water containing residual chlorine is too high. 4.2 Chlorination equipment Large and medium-sized water plants generally use liquid chlorine disinfection. Liquid chlorine and dry chlorine on copper, iron and steel and other metals have no corrosive properties, but when in contact with water or moisture, chemical activity to enhance the corrosiveness of the metal is very large, so in order to avoid chlorine bottles into the water, chlorine bottles in the chlorine can not be added directly to the water with the pipeline, it must be chlorinated after the machine to be added. There are many kinds of chlorine dosing equipment, commonly used vacuum chlorinator and rotor chlorinator. Vacuum chlorinator upper part of a glass cover, immersed in the water dish, the cover of the larger pressure gas pressure is low. Liquid chlorine cylinders of chlorine after depressurization gasification suction glass cover, by another pipe hole to the water injector, and pressure water mixing sent to the chlorination point. Chlorine in the cylinder of the rotor chlorinator first enters the cyclone separator, removes rust, oil and then through the spring membrane valve, control valve to the rotor flowmeter and the transit glass cover, in the water jet suction, chlorine and pressure water mixing and dissolution, chlorine concentration of more than 1%, through the chlorine pipeline to the chlorination point. Chlorination point should be selected in the unpressurized pipe canal. Recently, some domestic water plants have introduced more advanced foreign vacuum chlorination system, according to the flow of raw water and chlorine chlorine residual chlorine amount for automatic operation. Small water plants can be disinfected with bleach. The bleach used in its effective chlorine should reach 25%. Modulation and adding bleach solution should be two buckets, in order to take turns using. The solution barrel can be formulated into a concentration of 1% -2% of the bleach clarifier standby. Some water plants also use bleach concentrate tablets or sodium hypochlorite for disinfection. 5. Chlorination disinfection safety issues 5.1 Chlorination by-products of the formation and harm in the chlorination of disinfection to kill pathogenic microorganisms in the water at the same time, chlorine and organic matter in the water to react, resulting in a series of chlorine by-products. Usually, the organic matter in the water can form chlorination by-products with chlorine is called organic precursors. Natural water organic precursors to humus (humic acid and fulvic acid) as the main component, followed by algae and their metabolites, proteins and so on. Humus is the main precursor material for the formation of trihalomethanes, a chlorination by-product, in the process of chlorination disinfection. Trihalomethanes are volatile halogenated organic compounds, of which there are four main types: chloroform, monobromodichloromethane, dibromo monochloromethane and bromoform. Among them, chloroform has the highest content. According to studies, chloroform is mutagenic and carcinogenic to animals. Non-volatile halogenated organic by-products of chlorination include haloacetonitrile, haloacetic acid, halogenated phenols, halogenated ketones and halogenated aldehydes. These substances are difficult to be detected by the existing instruments, but they still have certain mutagenicity and carcinogenicity. 5.2 Preventive and curative measures For the prevention and control of chlorination by-products, the following measures can be taken according to the situation: selecting water sources with low content of organic precursors as far as possible; strengthening purification measures such as coagulation and precipitation and filtration; preventing the growth of algae in water-making structures to reduce the content of organic precursors; improving chlorination and disinfection methods such as canceling pre-chlorination and avoiding chlorine disinfection of the folding point, and adopting the chlorination of pipeline network halfway, etc., so as to reduce the formation of chlorination by-products; adopting granular activated carbon filtration; and using granular activated carbon filtration. The formation of chlorination by-products; the use of granular activated carbon filtration, in order to remove the formation of chlorinated by-products; in addition to consider the use of chlorine dioxide or ozone as an oxidizing agent / disinfectant, but also can be changed to chloramine disinfection. 6. Chlorine preparation effect determination for drinking water disinfection of chlorine-containing preparations are liquid chlorine, bleach, bleach tablets and sodium hypochlorite, etc., the disinfection effect depends on the content of effective chlorine, liquid chlorine containing effective chlorine in more than 99%; fresh bleach containing effective chlorine in 30% -35%; bleach tablets containing effective chlorine up to 60% -70%; just produced sodium hypochlorite in the effective chlorine of the chlorine. The effective chlorine content of the freshly produced sodium hypochlorite is 13%-14%. The effective chlorine content of bleach must be more than 25%, and the effective chlorine content of sodium hypochlorite should be more than 10% to be used as drinking water disinfectant. Determination of effective chlorine can be used iodometric method. The principle is: chlorine in acidic solution and potassium iodide oxidation, release a considerable amount of iodine, and then sodium thiosulfate standard solution to titrate the iodine, and then according to the dosage of sodium thiosulfate standard solution to calculate the content of effective chlorine in chlorine-containing compounds. Determination of effective chlorine in bleaching powder can also be simpler blue ink rapid determination method. Because the blue ink can be bleached by the effective chlorine, so it can be calculated according to the volume of blue ink consumption of effective chlorine content in bleaching powder. When chlorination is used to disinfect drinking water, three indicators will be involved: chlorination, chlorine demand and residual chlorine. Chlorination is the amount of chlorine added to the water. Chlorine demand is the amount of chlorine needed to disinfect drinking water. Residual chlorine is the amount of chlorine remaining in the water after the water has been exposed to chlorine disinfection for a certain period of time. Subtracting the amount of residual chlorine from the amount of chlorine added to the water is the amount of chlorine required by the water body. The role of residual chlorine in drinking water is to demonstrate the disinfection effect and to prevent recontamination of drinking water. Residual chlorine has three forms: total residual chlorine, chemical residual chlorine, free residual chlorine. China's drinking water health standards for centralized water supply water free residual chlorine content shall not be less than 0.3mg / L. Residual chlorine determination methods are: iodine amount of total residual chlorine, the principle of the same determination of effective chlorine; o-toluidine colorimetric method to determine the total residual chlorine and free residual chlorine, the principle of its PH less than 1.3 in acidic solutions, residual chlorine and o-toluidine reaction to generate yellow quinone compound, with visual colorimetric method. Compounds, with visual colorimetric method for colorimetric quantification; o-toluidine - arsenite colorimetric method can be determined in three forms of residual chlorine and interference with false color, its principle is that when the residual chlorine and o-toluidine to generate yellow compounds, and then add arsenite and its color no longer changes, such as the first to add arsenite to reduce the residual chlorine to chloride, the residual chlorine can not be with the o-toluidine role in the production of If the chlorine residual is reduced to chloride by adding arsenite first, the chlorine residual cannot interact with o-toluidine to produce yellow compound, and the color of the solution is the false color of the interfering substance. According to the order of addition of arsenite and o-toluidine and control of different color development time, free residual chlorine, compound residual chlorine and total residual chlorine content can be measured, and can remove false color interference. Due to the carcinogenicity of o-toluidine, this colorimetric method has been abolished internationally, and the DPD method is used to determine the residual chlorine (including free chlorine, compound residual chlorine and total residual chlorine) content in water. The principle is: chlorine and D.P.D in the acidic conditions, the generation of peach-colored product, the color of the color is proportional to the content of residual chlorine in the water. According to the different order of adding reagents, three different residual chlorine can be measured. Two other disinfection 1. Chlorine dioxide disinfection in the 1940s, some European countries found that chlorine dioxide (C102) for water disinfection has a very good effect, but because of the complexity of the manufacture, the price is more expensive, in the past has not been attached importance. In recent years, foreign countries to avoid the harmful effects caused by chlorine disinfection and looking for new disinfectants, it is increasing research and application, according to statistics, in 1977 the use of chlorine dioxide in Europe, thousands of water plants, the United States has 103 water plants using chlorine dioxide disinfection. China in the past two years there are also the use of chlorine dioxide disinfection of drinking water plant appeared. 1.1 physical and chemical properties of chlorine dioxide chlorine dioxide at room temperature for the orange-yellow gas, melting point -59.5 ℃, boiling point of 11 ℃, solubility in cold water 2.9 g / l (that is, 4 ℃ solubility), hot water in the decomposition of HCl02, C12 and O2. Chlorine dioxide is easily soluble in water, but does not react with the water chemical reaction in water is very easy to volatility in the water, the solution in water is yellowish-green, open for storage by the light. Decomposition. Therefore, it is not suitable for storage, must be used in the field while producing; stored in closed, light-proof conditions, it is very stable, if mildly acidified (PH6) is more stable. Chlorine dioxide is easy to explode, when the concentration in the air is more than 10% or the concentration in the water is more than 30%, are explosive. Therefore, it is common to use air to talk about chlorine dioxide gas during production, so that its concentration is lower than 8%-10%. When this gas is dissolved in water, the concentration of chlorine dioxide in water is about 6-8mg/L. Chlorine dioxide has strong oxidizing property under acidic condition. 1.2 Chlorine dioxide disinfection from the research data show that chlorine dioxide on bacteria, viruses and fungal spores are very strong killing ability, due to CLO2 is an unstable compound, does not contain H0Cl and H0Cl- form of chlorine, however, its concentration is often expressed in terms of effective chlorine. cl02 chlorine atom for the positive 4 valence, the reduction of chlorine into chloride will be able to get 5 electrons, so its oxidizing power is equivalent to chlorine 5 times, effective chlorine. Equivalent to 5 times the chlorine, effective chlorine content of 263%. Therefore, chlorine dioxide is extremely effective drinking water disinfectant. Chlorine dioxide on the killing principle of microorganisms is: chlorine dioxide on the cell wall has a good adsorption and permeability properties, can effectively oxidize the cell containing hydrophobic enzymes; can react with cysteine, tryptophan and free fatty acids, rapid control of biological protein synthesis, so that the membrane permeability increases; and can change the virus coat protein, resulting in viral inactivation. 1.3 Toxicity of chlorine dioxide Chlorine dioxide and its disproportionation of the formation of chlorite and chlorate have a certain degree of toxicity. C1O2- can cause hemolytic anemia and degenerative hemoglobinemia in animals, CLO2 also has the effect of lowering serum thyroxine. It has been proved by animal experiments that only when exposed to high concentrations of chlorine dioxide and the disproportionation product chlorite, adverse effects will occur; low-dose exposure generally does not affect their health. For example: some people use mice for experiments, drinking water containing chlorite 100mg / l, can make their hemoglobin content significantly reduced; drinking content of 10mg / l of water did not cause such changes. Let the rats drink chlorine dioxide 10mg / l of water for a long time, two years later also did not check the role of animal health hazards. 1.4 Chlorine dioxide disinfection CLO2 in the drinking water disinfection in addition to can be used alone, can also be used in conjunction with other disinfectants. Such as CL02 for water pre-treatment, and then add chlorine in the post-filtration water, which can prevent the formation of excess trihalomethanes, reduce the growth of algae on the structure, and can avoid the total amount of water in the pipeline network C102, C102- and CL03- is too high. CLO2 dosage and source water quality, in general, only for disinfection, adding 0.1-0.3mg / L, both for pre-treatment, about 0.6-1.5mg / L. But in any case, the remaining amount of chlorine should be the same as the free residual chlorine, and pipe network in the total amount of CL02, C102- and CL03- should be less than 1mg/L. Factors affecting the disinfection effect of chlorine dioxide is mainly temperature, with the lowering of the temperature of its bactericidal effect gradually weakened. But the disinfection effect is not affected by the PH value (PH6-10), which makes its water quality PH changes than chlorine has a stronger adaptability, especially for higher alkalinity source water disinfection; also not affected by the natural water source of ammonia that often exists; therefore, chlorine dioxide as a drinking water disinfection has its own unique practicality. 1.5 Advantages and disadvantages of chlorine dioxide disinfection Chlorine dioxide is a strong oxidant, it has the following unique advantages in water disinfection: can reduce the formation of chlorination by-products such as trihalomethanes in the water; when the water contains ammonia does not react with ammonia, the oxidation and disinfection of chlorine dioxide will not be affected; can kill pathogenic micro-organisms in the water and viruses; disinfection is not subject to the effect of water quality pH; after chlorine dioxide treatment. Chlorine dioxide treatment, the residual chlorine in the water is stable and long-lasting, the ability to prevent recontamination is strong; due to strong oxidation, can remove the color and taste of the water, not with the phenol to form chlorophenol odor; iron, manganese removal effect is stronger than chlorine; chlorine dioxide can be a safe production of aqueous solutions and use. The disadvantages are: chlorine dioxide is explosive, must be prepared on-site, immediate use; preparation of chlorine dioxide containing low chlorine is more complex, its cost is higher than other disinfection methods; chlorine dioxide disproportionate products of animals can cause hemolytic anemia and degenerative hemoglobin hemoglobinemia and other toxic reactions. 2. Ultraviolet disinfection 2.1 ultraviolet disinfection principle of pathogenic microorganisms with the killing effect of ultraviolet wavelength is mainly 200-300nm, of which 240-280nm wavelength of bactericidal power is stronger, 254nm wavelength of ultraviolet light bactericidal power is the strongest. Ultraviolet light on pathogenic microorganisms is the principle of killing: when microorganisms are irradiated, ultraviolet light can penetrate into the body of microorganisms in the nucleic acid, plasma proteins and enzymes, so that they undergo chemical changes and cause microbial death. According to research, ultraviolet light to make the DNA adjacent to the thymine bond synthesis of double body, to the loss of DNA transcription ability, pathogenic microorganisms die. 2.2 Ultraviolet disinfection methods with ultraviolet disinfection of drinking water, generally using ultraviolet drinking water disinfection device. Disinfection device is tubular, so that the water from one side into the other side of the outflow, the pipeline with ultraviolet light irradiation. Currently the UV lamps are high pressure quartz mercury lamps. There are two types of equipment used for drinking water disinfection: the casing-in type (immersion type) and the reflector type (surface type). Casing into the water is a quartz casing outside the lamp, the water from the lamp next to the flow and disinfection; reflector type is the use of polished aluminum surface reflector will be ultraviolet radiation into the water, the treated water for the unpressurized flow. The effective life of the lamp is 500h, the lamp is divided into low-pressure lamps and high-pressure lamps, high-pressure lamps sterilize more water per unit of time than low-pressure lamps. The use of ultraviolet disinfection, water color and turbidity should be low, the best depth of water is not more than 2cm, light contact time 10-100s. 2.3 Advantages and disadvantages of ultraviolet disinfection UV disinfection is the advantages of short contact time required, high sterilization efficiency, does not change the physicochemical properties of the water; does not produce residual substances and undesirable odors; disadvantages of disinfection of the water is no continuous Bactericidal effect, the amount of water handled by each lamp is limited, and the need for regular cleaning and replacement, (weekly application of alcohol cotton balls to rub the lamp), the cost is also more expensive. Therefore, in addition to the unit of water supply can be used in addition to ultraviolet disinfection, has not been widely used. 3. Ozone disinfection 3.1 Physical and chemical properties of ozone Ozone is also known as three oxygen. Ozone is the strongest known oxidant, at room temperature for the light blue explosive gas, has a special odor. Ozone gas can be liquid by low-temperature compression, boiling point of -112.3 ℃. The solubility of ozone in water is 13 times greater than that of oxygen, but because of the low partial pressure, it can only be obtained at room temperature and pressure of several milligrams per liter of the concentration of the solution. Ozone stability is very poor, at room temperature can be decomposed into oxygen, and release the new ecological oxygen: 3.2 Advantages and disadvantages of ozone disinfection Advantages of ozone disinfection are: disinfection effect is better than the C102 and CL2; dosage is small; contact time is short; PH in the range of 6-8.5 are effective; does not affect the organoleptic properties of the water, and at the same time there are deodorant, color, iron, manganese, phenol and other roles; In addition to bromide ions in the water, does not produce trihalomethanes; used in pre-treatment fashion can promote flocculation and clarification, reduce the amount of coagulant, and thus reduce the amount of chemical sludge. Disadvantages are: large investment, higher costs than chlorination disinfection; 03 in the water is not stable, control and detection of O3 require certain technology, the lack of residual disinfectant, no residual 03 factory water (03 on the pipeline corrosive effect of the strong, but also does not allow residual 03), so the need to use the second disinfectant, in order to prevent the growth of bacteria after the growth. Application of three disinfection methods 1. medium and large water plants At present, most of the water plants in China use chlorine disinfection. Chlorine disinfection effect is good, with continuous disinfection (pipe network residual chlorine), and the cost is lower than other disinfection methods. However, because chlorine is irritating and harmful gas, metal has a strong corrosive, so the use of chlorine disinfection must have a special chlorine machine, chlorine chlorine room and chlorine library to ensure the safety of chlorination. Usually will be equipped with liquid chlorine chlorine bottle on the scale, in the process of chlorination at any time to observe the weight of chlorine bottles degree, by checking the amount of chlorine bottles in the remaining amount of liquid chlorine, to prevent the use of empty, use should also be prevented from chlorine machine water backflow into the chlorine bottle. Because chlorine is heavier than air, chlorination room and chlorine library of the low wall of the installation of exhaust fans, in order to exclude the accumulation of chlorine indoors; chlorine library and chlorination room should be placed in the leakage detection alarms, in order to prevent and deal with chlorine leakage accidents, in the chlorination room there should be an emergency neutralization and treatment of pools (pools filled with lime water). After chlorination, should strengthen the continuous monitoring of chlorine residual, when possible, chlorination location should be set up chlorine residual continuous meter. At present, many large domestic water plants using automated chlorination, there are also water plants using computer-controlled chlorination. In order to reduce the growth of algae in the sedimentation tank and filter, some water plants use pre-filtration chlorination and post-filtration chlorination of the secondary chlorination method. However, pre-filtration chlorination can cause chlorine and organic matter in the water to react to the formation of trihalomethanes and other substances, so the current proposal in the pre-filtration ozone or chlorine dioxide disinfection, post-filtration chlorine disinfection method. Small water plants are currently using chlorine disinfection methods, but also bleach disinfection. Because of the effective chlorine contained in bleach is volatile, each batch of purchased bleach should be measured effective chlorine content. The warehouse for storing bleaching powder should be spaced apart from the bleaching powder solution and kept cool, dry and with good natural ventilation. Bleaching powder dissolving pool and solution pool generally 2, easy to use in turn. The slope of the bottom of the pool is not less than 2% and slopes to the slag hole. Because chlorine is corrosive, there should be anti-corrosion measures. Add bleaching powder room and - level pump room should be separated, and use natural ventilation, indoor floor slope is not less than 5%. Bleaching powder feeding method: each package of 50kg of bleaching powder first add 400-500kg of water stirred into 10%-15% of the solution, and then add water to adjust to 1%-2% concentration, after clarification, from the measurement of the equipment into the post-filtration water, can be used by gravity will be added to the bleaching powder solution to the suction pipe of the pump, but also can be used in water jets to the pressure pipe to be added. 2 enterprises, rural water plants 2.1 enterprise water plant disinfection enterprises due to small water supply, pipe network is relatively centralized, the current use of drinking water disinfection methods. Chlorination disinfection, bleach disinfection, ozone disinfection, ultraviolet disinfection and chlorine dioxide disinfection, and some use of sodium hypochlorite disinfection. Sodium hypochlorite is produced by sodium hypochlorite generator after electrolysis of table salt, and its effective chlorine content is 1%-5%. Sodium hypochlorite is susceptible to decomposition by sunlight and temperature, therefore, sodium hypochlorite should be prepared and dosed locally. The effective chlorine content of industrially prepared sodium hypochlorite is 10%-12%, but due to its instability, its effective chlorine content should be tested when purchased. Storage time should be within 1 month. The dosing method should be by gravity, through the water sealing box to the water pump suction pipe, or water injector to the pressure pipe. Dosing concentration to effective chlorine content in l-6mg / L per ton of water about 10-60ML sodium hypochlorite solution. 2.2 Rural water plants Rural water plants to deep wells and water towers of the water supply mode is more, but also the use of ground water and fully treated water supply production methods. Drinking water disinfection of rural water plants according to their economic conditions and choose different methods, most of the bleach disinfection, but also the use of sodium hypochlorite disinfection, a small number of water plants using liquid chlorine disinfection, ozone disinfection, chlorine dioxide disinfection and ultraviolet disinfection. 3. Rural decentralized water supply China's rural decentralized water supply surface there is still a considerable proportion, in order to ensure the health and safety of drinking water quality, well water must be disinfected frequently, especially in the season of enteric infectious diseases can not be ignored. Disinfection of well water can be used ordinary disinfection method and continuous disinfection method. Ordinary disinfection method that every day to the well cast bleach (or bleach) solution. Before disinfection, the depth and diameter of the well should be measured, and the amount of well water should be calculated. When possible, take a sample of well water for chlorine determination. According to the amount of well water and chlorine (or chlorine demand) calculated each time the disinfection of bleach (its effective chlorine content should also be measured in advance) weight. Bleach powder with water into a paste, and then add water mixing, the clarified liquid poured into the well, with a clean bucket or bamboo pole in the well stirring, half an hour later, from the well to take water samples to determine the residual chlorine content, so that to remain in the 0.3-0.5mg / L is appropriate. If the residual chlorine is not enough or too much, the amount of added medicine is too little or too much, should be used as a reference for the next disinfection. Well water disinfection is generally 2 times a day, once in the morning before the masses of water, once in the afternoon.