Definition and basic properties of hypochlorous acid
Hypochlorous acid (HClO) is a monobasic weak acid with a chemical formula of HClO and a molecular structure of H-O-Cl, where the valence of the chlorine element is +1. It is an unstable acid with strong oxidizing and bleaching effects. It usually exists in the form of an aqueous solution. The concentrated solution is light yellow and the dilute solution is colorless.
Hypochlorous acid is weakly acidic, with a pKa value of about 7.5 and an ionization constant of 3×10⁻⁸. It is partially ionized in water to H⁺ and ClO⁻, so it has weak acidity.
Hypochlorous acid also has important applications in biology and medicine, such as as an endogenous antibacterial agent produced by white blood cells to fight bacteria, viruses and fungi. It is widely used in disinfection, sterilization and wound care in the medical industry because of its broad-spectrum antibacterial activity and low toxicity.
Hypochlorous acid is an important chemical substance with weak acidity, strong oxidizing and instability. It is widely used in disinfection, bleaching, water treatment and medical fields.
List of common disinfection methods
Common disinfection methods include the following:
- Physical disinfection: using physical factors to kill pathogenic microorganisms, such as thermal disinfection (boiling, steam, high-pressure steam), ultraviolet disinfection, ozone disinfection, dry heat disinfection (such as burning, electric heating), radiation disinfection (such as gamma rays, X-rays), etc.
- Chemical disinfection: using chemical disinfectants for disinfection, such as alcohol, bleach, peracetic acid, glutaraldehyde, chlorhexidine, iodine phenol, etc. According to the different effectiveness, it can be divided into high-level, medium-level and low-level disinfectants.
- Biological disinfection: using biological factors to kill pathogenic microorganisms, such as certain microorganisms or enzyme preparations, but it is currently less common.
- Physical and chemical disinfection: combining physical and chemical methods for disinfection, such as ethylene oxide gas sterilization, hydrogen peroxide low-temperature plasma sterilization, etc.
- Other special disinfection methods: such as ultrasonic disinfection, copper-silver ionization, ozone disinfection, ultraviolet disinfection, etc.
These methods have their own advantages and disadvantages and are suitable for different scenarios and items, such as food, medical equipment, environmental surfaces, etc.
The bactericidal effect and action time of HOCL
The bactericidal effect of hypochlorous acid is closely related to its action time. Studies have shown that hypochlorous acid is related to pH value in solution state. When the pH value is 6 and the temperature is 2-5℃, 99% of Escherichia coli can be killed within 30 minutes. In addition, the bactericidal mechanism of hypochlorous acid is mainly related to its small molecular size and uncharged characteristics. It can quickly penetrate the cell membrane of microorganisms and destroy its protein, nucleic acid and enzyme system, thereby causing the death of microorganisms.
In practical applications, the bactericidal effect of hypochlorous acid shows significant advantages. For example, hypochlorous acid water with an effective chlorine content of 50mg/L can inactivate influenza virus, norovirus, etc. within 15 seconds, while it takes 30 seconds to kill Bacillus subtilis black variant spores. In some experiments, hypochlorous acid water can kill Escherichia coli, Salmonella, Staphylococcus aureus and other bacteria within 1 minute. In addition, the bactericidal effect of hypochlorous acid can reach 99.99% in a short time, and the action time is as short as 5~20 seconds to complete the sterilization.
The bactericidal effect of hypochlorous acid depends not only on its concentration and pH value, but also on the type of microorganism. For example, hypochlorous acid has a good killing effect on bacteria such as Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa, but it takes longer to kill some spore-like microorganisms (such as Bacillus subtilis black variant spores). In addition, hypochlorous acid also has a significant killing effect on viruses, such as influenza A virus and polio virus.
The bactericidal effect of hypochlorous acid can reach high efficiency in a short time, and the action time is short, usually between 15 seconds and 30 minutes, depending on the concentration, pH value and type of microorganism.
Comparison of the bactericidal effects of various disinfection methods
- Ozone disinfection: Ozone has strong oxidizing properties and has a good killing effect on bacteria, viruses and spores, with a bactericidal rate of up to 91.82%. Its sterilization speed is fast, but the operation safety is not high, and it is harmful to the respiratory tract, and it is not allowed to be used in the air supply system.
- Ultraviolet disinfection: Ultraviolet rays have a good sterilization effect on bacteria and viruses, with a sterilization rate of about 82.86%, but the killing effect on spores is weak. Ultraviolet disinfection is fast, but the equipment installation is complicated and the turbidity requirement is high.
- Chlorine dioxide disinfection: Chlorine dioxide has a good killing effect on bacteria, viruses and spores, with a high sterilization rate, but the operation safety is not high, the equipment installation is complicated, and the operation and maintenance costs are high.
- Liquid chlorine disinfection: Liquid chlorine is partially effective against bacteria and viruses, but ineffective against spores. The sterilization effect is moderate, the operation safety is low, but the operation and maintenance costs are low.
- Peracetic acid and hydrogen peroxide disinfection: These two disinfectants have a good killing effect on bacterial spores, the sterilization rate exceeds 5.00-log, and there is no harmful residue, which is suitable for disinfection of infectious disease epidemic sources.
- Complex iodine disinfectant: The killing rate of MS2 bacteriophage is as high as 99.78%, which is one of the better disinfectants.
- Chlorine-containing disinfectant: The killing rate of MS2 bacteriophage is 84.80%, which is a good effect, but may produce by-products.
- Compound quaternary ammonium salt disinfectant: The killing rate of MS2 bacteriophage is 93.80%, which is a good effect.
- Glutaraldehyde and Shile Sterilizer: In the disinfection of operating room air, the effects of these two methods are better than other methods and can effectively kill various pathogens.
- Acid/alkaline phenol salt solution: The antibacterial effect on G+ cocci is stronger than other disinfectants, such as 0.4% chlorhexidine acetate solution and 0.1% chlorhexidine solution.
- Building system acidic oxidizing potential water: In the disinfection of object surfaces in intensive care units, its sterilization rate is lower than that of chlorine-containing disinfectants and sanitary wipes, but the effect can be improved by increasing the frequency of disinfection.
- Formaldehyde disinfection: It is partially effective against bacteria and viruses, but ineffective against spores, and may produce irritating odors.
- Hydrogen peroxide disinfection: The killing rate of MS2 bacteriophage is 58.67%, which is a weak effect.
- Ethanol disinfection: 75% ethanol has a good killing effect on bacteria, but it is ineffective against spores, and attention should be paid to the concentration and safety issues.
- 75% ethanol: The killing rate of MS2 bacteriophage is 71.87%, which is a good effect, but not as good as complex iodine and compound quaternary ammonium salt disinfectants.
In summary, ozone, ultraviolet rays, chlorine dioxide, peracetic acid and hydrogen peroxide have good sterilization effects, while liquid chlorine, formaldehyde, ethanol and other methods have medium or weak effects. The selection of appropriate disinfection methods needs to be considered comprehensively according to specific application scenarios, safety, cost and other factors.
Safety and residue analysis of hypochlorous acid
Hypochlorous acid (HClO) is a weak acid with good oxidizing properties and is widely used in disinfection, formaldehyde removal and other fields. Its safety is mainly reflected in the following aspects:
- Low toxicity: Hypochlorous acid is non-irritating to the human body at low concentrations, and has no obvious toxicity through oral administration, inhalation, and skin contact. The US FDA has listed it as a food additive, and the residues on the food contact surface are exempted from the limit requirements, indicating that it is relatively safe.
- No residue: Hypochlorous acid will quickly decompose into water, oxygen, and chloride ions after use, and will not leave harmful residues in the environment. For example, after spraying or soaking, hypochlorous acid water will not remain in food, nor will it pollute the environment.
- Environmental protection: Hypochlorous acid can decompose on its own in the natural environment and will not produce harmful substances such as dioxins. In addition, it has low corrosion to metals and fabrics and is suitable for use in a variety of scenarios.
- Wide applicability: Hypochlorous acid can be used in hospitals, maternal and child care, food processing, agriculture and other fields, and is relatively safe for children and pets. For example, hypochlorous acid can be used to disinfect baby pacifiers, pet toys, etc.
However, hypochlorous acid may be risky when used in high concentrations or improperly. For example, high concentrations of hypochlorous acid may irritate the skin and eyes, and even cause chlorine poisoning. In addition, sodium hypochlorite (NaOCl), as a precursor of hypochlorous acid, may have certain health effects due to its residues, but hypochlorous acid itself is safe under reasonable use.
Anolyte water is an efficient, safe and environmentally friendly disinfectant under correct use and storage conditions, and has good application prospects.
Safety comparison of various disinfection methods
- Liquid chlorine disinfection: The operation safety is general, but there is a risk of chlorine leakage and explosion, and carcinogens such as trihalomethanes (THM) may be produced.
- Chlorine dioxide disinfection: The operation safety is relatively high, but the equipment is complex and explosive, and needs to be prepared on site.
- Ozone disinfection: The operation safety is general, but its disinfection effect is good, and the toxic effect on the biota is basically eliminated, but the operation and maintenance costs are high.
- Ultraviolet disinfection: The operation safety is relatively high, there is no chemical residue, but the requirements for the SS of the treated water are high, and there is no continuous disinfection effect.
- Sodium hypochlorite disinfection: The operation safety is relatively high and it is easy to store, but the use cost is high and it is easy to volatilize and decompose.
- Peracetic acid/hydroxide disinfection: The operation safety is general, it may cause irritation to materials and human body, but the sterilization effect is good.
- High temperature disinfection: The operation safety is high, no harmful substances are produced, but the energy consumption is high.
- Ozone (O₃) disinfection: The operation safety is general, but the disinfection effect is good, and it can remove odor and some organic matter.
- Lactic acid disinfection: The operation safety is high, but it needs to be kept away from oxygen and heating devices, and the effect is affected by the environment.
- Potassium persulfate compound salt disinfection: The operation safety is high, it does not contain chlorine, has strong disinfection ability, and is suitable for a variety of scenarios.
In summary, different disinfection methods have their own advantages and disadvantages in terms of safety, disinfection effect, cost and applicability. When choosing, it is necessary to weigh the specific application scenarios and needs.
Safety and environmental protection comparison of hypochlorous acid
- Non-toxic residue: After the action, it decomposes into water, sodium chloride and trace carbon dioxide. The US FDA has approved it for use on food contact surfaces (≤200ppm) without secondary rinsing.
- Biocompatibility: Human immune cells naturally secrete hypochlorous acid to kill bacteria, which is non-irritating and non-sensitizing at a concentration of 50-100ppm.
- Environmental protection: Natural decomposition is pollution-free and does not produce harmful substances such as dioxins.
Applicable scenarios
- Medical: surgical instruments, wound disinfection (alternative to iodine).
- Food processing: fruit, vegetable, and tableware disinfection (FDA approved).
- Public space: air and surface disinfection in schools and hospitals (human-machine coexistence).
- Limitations:
- Short shelf life (1-2 weeks), needs to be stored away from light.
- Corrodes carbon steel and aluminum products, not suitable for silk and wool fabrics.
Economic comparison
- Hypochlorous acid: The equipment is complex to install, but the operating cost is low (especially in high-frequency use scenarios).
- Ultraviolet rays: The equipment maintenance cost is high and there is no sustained effect.
- Liquid chlorine: The cost is the lowest, but the safety risk is high.
Comprehensive conclusion: The irreplaceable nature of hypochlorous acid
- Balance between high efficiency and safety: In terms of broad-spectrum sterilization speed (seconds) and biosafety, hypochlorous acid is one of the few disinfectants that can simultaneously meet the needs of medical, food, and public spaces.
- Environmentally friendly: The decomposition products are harmless and in line with the trend of sustainable development.
- Limited applicability: Short shelf life and corrosiveness limit its application in some scenarios, and it needs to be combined with other methods (such as ultraviolet assistance).
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