While both hypochlorous acid (HOCl) and bleach are chlorine-based disinfectants, they have significant differences in their chemical composition, efficacy, safety, and environmental impact. Understanding these differences is crucial for choosing the most appropriate disinfection method for various applications.
Chemical Composition and pH
Bleach, predominantly sodium hypochlorite (NaOCl), is a strong base with a high pH of around 11-13. When added to water, it forms a mixture of hypochlorite ions (OCl-) and a small amount of hypochlorous acid (HOCl). The ratio of OCl- to HOCl depends on the pH of the solution, with higher pH favoring OCl-.
In contrast, electrolyzed water containing hypochlorous acid has a near-neutral pH of around 6-7. At this pH, the chlorine exists predominantly as HOCl, which is the most effective form for disinfection. This pH range is also much closer to that of human skin and mucous membranes, making it less irritating and safer for use.
Efficacy and Mode of Action
HOCl is significantly more effective as a disinfectant than OCl-. Studies have shown that HOCl can be up to 80-100 times more efficacious than OCl- in killing pathogens. This is due to its neutral charge, which allows it to penetrate cell walls more easily.
Hypochlorous acid works by oxidizing key cellular components of microorganisms, disrupting cell membranes, and denaturing proteins. It acts quickly, often achieving a 3-log reduction (99.9% kill) of bacteria within seconds of contact.
Bleach, while still an effective disinfectant, requires much higher concentrations to achieve similar results. This is because much of the chlorine in bleach exists as the less effective OCl- ion. To compensate, bleach solutions typically contain much higher levels of total chlorine compared to HOCl solutions.
Safety and Environmental Impact
The high pH of bleach makes it corrosive and potentially harmful to skin, eyes, and mucous membranes. It can also damage surfaces over time and may produce toxic chlorine gas if mixed with certain other chemicals.
Hypochlorous acid, at the concentrations used for disinfection, is non-toxic and non-irritating to skin and eyes. It’s so safe that it’s often used in wound care and eye care products. HOCl also breaks down quickly into simple salt and water, leaving no harmful residues.
From an environmental perspective, the production and use of bleach can have significant impacts. The chlor-alkali process used to manufacture bleach is energy-intensive and can result in mercury emissions if older technology is used. The high pH of bleach can also harm aquatic ecosystems if not properly neutralized before disposal.
Electrolyzed water containing HOCl, on the other hand, can be produced on-site using only salt, water, and electricity. This eliminates transportation and storage issues associated with bleach. Its rapid breakdown into harmless components also means it has minimal environmental impact when disposed of.
Academic Sources:
- de Vargas Brião, G., da Costa, T. B., Antonelli, R., & Martins Costa, J. (2024). Electrochemical processes for the treatment of contaminant-rich wastewater: A comprehensive review. Chemosphere. https://doi.org/10.1016/j.chemosphere.2024.141884
- Ding, T., Oh, D.-H., & Liu, D. (Eds.). (2019). Electrolyzed water in food: Fundamentals and applications. Springer. https://doi.org/10.1007/978-981-13-3807-6
