(1) liquid chlorine disinfection
Adding chlorine to water will produce a series of chemical changes. The chemical reaction process of different water quality is different, but the final disinfection products are hypochlorous acid and hypochlorous acid ions.
1. When there is no ammonia nitrogen in the water.
CL2+HO2→HOCL+h++ CL–……………。 ( 1)
Hypochloric acid is a weak electric medium.
HOCL→h++ OCL—………………………………(2)
The ratio of hypochlorous acid to hypochlorous acid in water mainly depends on the pH value of water. Both HOCL and OCL- have oxidation ability, but HOCL is a neutral molecule, which can spread to the surface of negatively charged bacteria and penetrate into the bacteria. The oxidation of chlorine atoms destroys enzymes in bacteria, leading to the death of bacteria. Close is negatively charged, so it is difficult to get close to negatively charged bacteria, so it is difficult to disinfect even if it has oxidation ability.
As can be seen from Figure 1, in the range of pH 5.6-9.5, the lower the pH value of water, the greater the percentage content of HOCL, so the better the disinfection effect.
2. When there is ammonia nitrogen in water, HOCL generated by formula (1) will be ammoniated to generate a class of compounds called amines, and its composition depends on the pH value of water and the ratio of CL2 to NH3 content.
NH3+HOCL →NH2CL+H2O……(3)
NH3+2 hocl→nhcl 2+2H2O…………………………(4)
NH3+3HOCL →NCL3+3H2O……(5)
When the PH value of water is between 5 and 8.5, NH2CL and NHCL2 exist at the same time, but when the PH value is low, there are more NHCL2, which has strong bactericidal ability, so the PH value of water is low, which is also beneficial to disinfection. NCL3 _ 3 can only be produced when the PH value is lower than 4.4, and it is unlikely to be formed in ordinary drinking water.
Therefore, whether there is ammonia nitrogen in the water or not, the lower the pH value is in the range of 6.8-8.5, the better the disinfection effect is than that of high pH value.
(2) Chlorine dioxide disinfection
Chlorine dioxide is chemically active and easily soluble in water. At 20℃, its solubility is 107.98g/L, which is five times that of chlorine. The oxidation capacity is twice that of chlorine. CLO2 _ 2 _ 2 is a neutral molecule, which exists in the molecular state of almost 100% in water, so it is easy to penetrate the cell membrane and penetrate into bacterial cells, and its nucleic acid (DNA or RNA) will be oxidized, thus preventing bacterial anabolism and leading to bacterial death. The chlorine dioxide sterilization reaction in drinking water is shown in the following formulas (6) and (7).
Chlorine dioxide +e→ chlorine dioxide (6)
clo 2+2H2O+4e→CL –+ 4OH –………………( 7)
The experimental results show that the electrode potential of formula (6) is 0.95V and that of formula (7) is 0.78V V. Therefore, chlorine dioxide disinfection can also oxidize some reducing metal ions (such as Fe2+ Mn2+, etc.). ) in water, it has a good removal effect on iron and manganese in water. The oxidation ability of ClO _ 2 is related to the pH value of the solution. The stronger the acidity of the solution, the stronger the oxidation ability of ClO _ 2. But in the range of PH 6- 10, the germicidal efficacy is almost unaffected by PH value.
To sum up, under the conditions of water purification process, HOCL is a disinfectant mainly composed of liquid chlorine, and its bactericidal effect is nearly 80 times higher than that of OCL-as can be seen from Table 1, the higher the pH value, the more HOCL dissociates. When the pH value is greater than 8, it will reach 75% OCL-, and the disinfection effect will be reduced. The results of many experiments show that chlorine dioxide can kill bacteria in a certain range, and liquid chlorine can only kill bacteria effectively under near-neutral conditions.
Two kinds of disinfectants kill bacteria in drinking water.
The purpose of adding disinfectants to drinking water is mainly to kill pathogenic bacteria, germs and other pathogenic microorganisms harmful to human body. Disinfecting water can't kill all bacteria in water, but it can contain a small amount of bacteria harmless to human health, but it must meet the requirements of Hygienic Standard for Drinking Water.
(A), the influence of disinfectant dosage on disinfection effect
In order to study the influence of adding two pairs of disinfectants on disinfection effect, the bacteriological indexes of precipitation water (without disinfectants), pre-filtered water (with 1.5 mg/L disinfectants) and filtered water (with 1.5 mg/L disinfectants) in our company were tested, and the test results are shown in Figure 2.
From the test results, it can be concluded that:
1. chlorine dioxide and liquid chlorine have good bactericidal effect on Escherichia coli, and the bactericidal rate increases with the increase of dose; The bactericidal effect of chlorine dioxide is slightly better than that of liquid chlorine. When the dosage is 1.5mg/L, the sterilization rate of liquid chlorine and chlorine dioxide is 94.76% and 97.62%, respectively.
2. Chlorine dioxide is obviously superior to liquid chlorine in killing bacteria.
(2) The influence of water temperature on the germicidal efficacy of disinfectant.
The bactericidal ability of disinfectants increases with the increase of temperature. When the temperature is low, the bacterial mortality increases exponentially with each increase of 10℃. Chart ⅲ shows the relationship between the contact time of chlorine dioxide and the survival rate of Escherichia coli at different temperatures. As can be seen from the figure, with the increase of temperature, the sterilization time is relatively shortened and the sterilization effect is relatively enhanced.
Third, the influence of two disinfectants on the formation of organic halogenated compounds in drinking water
With the research on the carcinogenic effect of organic halides produced by liquid chlorine disinfection of drinking water, the National Natural Science Foundation funded a project to compare the treatment of organic substances in water with liquid chlorine disinfection and chlorine dioxide disinfection. Four kinds of concentrated water samples from drinking water disinfected by liquid chlorine and chlorine dioxide from the same waterworks were analyzed by gas chromatography/mass spectrometry. The test results are shown in Figure 4.
The experimental results show that when adding liquid chlorine for disinfection, not only are there many kinds and contents of organic substances, but also more organic halides (such as CHCl3 and CHBr3) are generated. For example, 2 kinds of chlorinated compounds and 7 kinds of brominated compounds were detected in water samples with 0.7 mg/L liquid chlorine, with the content of 9.76%; However, no organic halogenated compounds were detected in the water samples disinfected with chlorine dioxide. Chlorine dioxide disinfection generally only plays the role of oxidation, not chlorination, which is the fundamental reason why chlorine dioxide disinfection hardly forms organic halogenated compounds. It can be seen that chlorine dioxide is the best choice when the source water is seriously polluted or the organic matter content in the water body is high.
Four, the rational use of drinking water disinfectants in our factory
The principle of preparing disinfectant with high-efficiency compound chlorine dioxide generator introduced by our factory is that sodium chlorate aqueous solution and hydrochloric acid solution fully react at a certain temperature and negative pressure to generate disinfection gas with chlorine dioxide as the main component and chlorine as the auxiliary component to disinfect drinking water.
At the initial stage of equipment operation, the rust in the pipe scale will consume a part of chlorine dioxide, resulting in a large consumption of chlorine dioxide and high operating cost. After running for about one month, the dosage of chlorine dioxide tends to be stable. Production practice cost statistics and economic and technical analysis show that the consumption of chlorine dioxide is lower than that of liquid chlorine, but the cost of raw materials for preparing chlorine dioxide is 0.02 yuan/ton higher than that of liquid chlorine when the same disinfection effect is achieved. In order to ensure water quality and save costs, our factory uses liquid chlorine for disinfection when water pollution and turbidity are low in winter. In summer, when the water source is seriously polluted or the organic matter content in the water source is high, chlorine dioxide is used for disinfection.
Verb (abbreviation of verb) conclusion
As a classical disinfection method of drinking water, liquid chlorine has the advantages of strong disinfection ability, sufficient supply, low price, simple dosing equipment and low price. However, when the content of organic matter in water is high, halogenated organic matter with carcinogenic effect will be produced.
As a later developed disinfection method, chlorine dioxide has stronger sterilization ability than liquid chlorine disinfection, and the sterilization effect is not affected by the pH value of water. Only when oxidation does not occur chlorination can the disinfection effect be achieved, thus avoiding the problem of organic halides. But chlorine dioxide must be used when it is taken out, and it cannot be preserved, so the raw materials are expensive.
Liquid chlorine disinfection and chlorine dioxide disinfection have their own advantages and disadvantages. I should choose drinking water disinfectant reasonably according to the actual situation in production practice, and strive to get the best cost performance.
I. Types and Mechanism of Veterinary Disinfectants
There are many kinds of disinfectants, and the commonly used disinfectants for animals mainly include phenol, aldehyde, alcohol, acid, alkali, chlorine preparation, iodine preparation, heavy metal salt and surfactant.
Disinfectants such as phenols can denature and precipitate pathogenic microorganisms and kill general bacteria. Compound phenol can kill spores, viruses and fungi. Mainly phenol, compound phenol, coal phenol and so on.
Aldehydes have a strong bactericidal effect, among which formaldehyde has a better effect and is the most commonly used. With the progress of production technology and the demand of aquaculture, efficient disinfectants such as glutaraldehyde and phthalaldehyde are also widely used.
The sterilization principle of acid disinfectants is that high concentration of hydrogen ions can denature and hydrolyze bacteria protein, while low concentration of hydrogen ions can change the dissociation degree of amphoteric substances on the protein of bacteria surface, inhibit the permeability of cell membrane, and affect the absorption, excretion, metabolism and growth of bacteria. Hydrogen ions can also compete with other cations to adsorb on the surface of bacteria, which hinders the normal activities of bacteria.
Alkaline disinfectants used for livestock and poultry disinfection mainly include caustic soda, caustic potash, lime, plant ash and soda ash. The mechanism of alkali disinfection is that negative hydroxide ions can hydrolyze protein and nucleic acid and destroy the enzyme system and cell structure of bacteria. At the same time, alkali can also inhibit the normal metabolic function of bacteria, decompose sugars in bacteria and revive bacteria. It has a powerful killing effect on viruses, and can be used for disinfection of various viral infectious diseases, and high-concentration lye can also kill spores. Alkaline disinfectants are most commonly used to disinfect farm areas and fences, contaminated equipment (anti-corrosion) and various items, as well as excreta and waste containing pathogens.
Alcohols Alcohols are mainly used for disinfection of skin, instruments, injection needles and thermometers, such as 75% alcohol.
Disinfectants such as surfactants, also known as detergents or detergents, can reduce the surface tension of bacteria, facilitate the emulsification of oil and remove oil stains, and produce certain cleaning effects. In addition, surfactants can also be adsorbed on the surface of bacteria, changing the permeability of cell membrane, enabling the selection of enzymes, coenzymes and intermediate metabolites in bacteria, hindering the process of bacterial respiration and glycolysis, denaturing bacteria protein and producing sterilization. Commonly used are bromogeramine, chlorhexidine and domiphen.
Oxidant This is a compound containing unstable bound oxygen, which can release nascent state oxygen when it meets organic substances or enzymes, thus destroying the active genes of bacteria and playing a disinfection role. Commonly used oxidant disinfectants are potassium permanganate and peracetic acid.
Halogen (including chlorine, iodine, etc. ) has a high affinity for bacterial protoplasm and other structural components, easily permeates into cells, and then combines with amino groups or other groups of bacterial protoplasm protein, so that its bacterial organic matter decomposes or loses its function, showing bactericidal effect. Among halogens, fluorine and chlorine have the strongest bactericidal power, followed by bromine and iodine, but fluorine and bromine are generally not used for disinfection. Commonly used disinfectants are: bleaching powder essence, sodium hypochlorite solution, excellent chlorine, strong disinfectant, tincture of iodine, compound complex iodine and so on.
Second, the present situation of evaluation test of disinfectant sterilization effect
The evaluation of disinfection effect in disinfection products should be based on the Technical Specification for Disinfection promulgated by the Ministry of Health of the People's Republic of China in 2002. However, there are still many problems in some experimental methods and operation techniques specified in this specification. The evaluation of disinfection effect is mainly to evaluate the killing effect of microorganisms (bacteria, viruses, fungi, spores, etc.). ) and the influence of organic matter, PH value, temperature and other factors on its effect.
According to the Technical Specification for Disinfection (2006 exposure edition), The basic experimental strains selected to detect the inactivation effect of disinfection products on bacteria and fungi are: Staphylococcus aureus ATCC 6538, Pseudomonas aeruginosa ATCC 15442, Escherichia coli 8099, Bacillus subtilis ATCC 9372, Mycobacterium chelidonii abscess subspecies ATCC 19977, Staphylococcus albicans ATCC/ Kloc-0/023 1, Aspergillus on the basis of the above-mentioned designated strains, other strains can be selected according to the specific use of disinfectants or the special needs of experiments. The experimental virus strains used for virus inactivation test are poliovirus-I1(PV-I) vaccine strain and HIV 1 (human immunodeficiency virus, HIV- 1) American strain.
The detection methods for evaluating the disinfection effect of disinfectants mainly include neutralization test, qualitative disinfection test, quantitative disinfection test, sterilization energy test and antigenicity destruction test of hepatitis B surface antigen. Please refer to the evaluation methods and standards of disinfection and sterilization effect proposed by the Ministry of Health for specific detection steps.
Third, the application status of veterinary disinfectants
At present, the most widely used veterinary disinfectants in China are compound phenols, iodine, quaternary ammonium salts and chlorine preparations. At present, the effective disinfectants widely used in aquaculture units mainly include:
Mi An produced by Schering-Plough Company mainly consists of glutaraldehyde 15% and coconut oil quaternary ammonium salt10%;
Bai Jing Bayer animal protection production, the main component is dodecylamine triiodide oxide;
Delicious! -30/ 15 is produced in Pfizer and mainly contains iodine, phosphoric acid and sulfuric acid.
DuPont chemical products of Nongfu Spring, the main component of which is high-efficiency compound phenol.
There are still many problems in the practical application of veterinary disinfectants, such as ignoring the removal of organic matter such as feces, feed residues and body surface shedding in livestock houses; It is considered that drinking water disinfectant is harmless to livestock and poultry, and the concentration is increased at will, causing losses; It is considered that using warm water as solvent can increase the disinfection effect of all disinfectants. Unable to cross-apply multiple types of disinfectants, resulting in drug resistance; It is considered that the stronger the smell of disinfectant, the better, which will cause mucosal damage of livestock and poultry and affect the benefit.
Fourth, look ahead.
With the globalization of economy and trade, the prevalence of animal diseases is also globalized, and the prevalence of some new diseases has caused great losses to livestock and poultry breeding. Because the research of new infectious disease vaccine needs a long period, only by strengthening feeding management and paying attention to disinfection and other preventive measures can the prevention and control of new infectious diseases be realized. In this case, it is necessary to study one or more new, efficient, broad-spectrum and safe disinfectants.
The ideal disinfectant for animals should have the characteristics of high efficiency, broad spectrum, rapid action, long-lasting activity, stable properties, convenient storage and transportation, resistance to organic interference, high safety and moderate cost. New and efficient compound disinfectants and special surfactants for veterinary disinfectants will become the research trend in the future. On this basis, people will gradually pay attention to the research of more detailed professional and practical disinfectants such as special disinfectants for pet surgery (instruments), special disinfectants for cow nipples, special disinfectants for breeding eggs, special disinfectants for SPF animal barrier facilities, special disinfectants for biosafety laboratories and special disinfectants for vaccine inactivation.
Extended reading
Problems existing in supervision of veterinary disinfectants
The name of disinfectant is complicated. There are many manufacturers specializing in the production of veterinary disinfectants in China, and there are many kinds of disinfectants sold in the veterinary drug market. Besides domestic products, there are some imported medicines. There are many kinds of animal disinfectants, and the same function has dozens or even hundreds of products with different approval numbers, which makes it difficult for users to choose disinfectants.
Manufacturers deliberately exaggerate the disinfection effect. In order to cater to consumers' consumption psychology and promote product sales, some manufacturers deliberately exaggerate the disinfection effect of products in product packaging instructions, use absolute language, and even describe their products as "panacea".
Due to the imperfection of the relevant regulatory system, some operators take advantage of the negligence of the regulatory agencies, which makes a large number of inferior disinfectants flow into the veterinary drug market, which not only destroys the original market order, but also causes huge economic losses to the relevant breeding units. At the same time, producers of inferior disinfectants also use the bad psychology of taking kickbacks from veterinary drug sales to enter the market. The profit-driven phenomenon of these disinfectant price rebates has a negative impact on the management of disinfectants.
Lack of scientific research on related drugs The research on veterinary disinfectants involves the knowledge of disinfection, veterinary epidemiology, environmental hygiene and veterinary microbiology, which is time-consuming and laborious. At the same time, the advent of a disinfectant has to go through several steps, such as laboratory research, pilot scale-up and clinical practice, and it takes a long time to transform it into a product. At present, many disinfectants used are studied by health departments and prevention and quarantine departments, but there is a lack of experimental research on veterinary disinfectants.