Disinfection for drinking water serves a crucial purpose—eradicating a vast majority of harmful pathogenic microorganisms, including bacteria, viruses, and protozoa, to prevent the spread of waterborne diseases. While disinfection doesn’t eliminate all microorganisms, it ensures that the risk of waterborne diseases is minimized to levels deemed acceptable under microbiological standards. Sterilization, on the other hand, refers to eliminating all microorganisms present in the water, while disinfection targets a substantial portion of pathogenic microorganisms, reducing risks associated with waterborne illnesses.
Evolution of Disinfection Techniques
Before the mid-19th century, when the bacterial pathogenic theory was established, odor was considered a medium for disease transmission, influencing the development of water and sewage disinfection practices.
Disinfection Methods for Drinking Water
Physical Disinfection
Physical methods such as heating, filtration, ultraviolet (UV) radiation, and irradiation are employed. Boiling water is common, effective for small-scale treatment, while filtration methods like sand, asbestos, or fiber vinegar filters remove bacteria without killing them. UV radiation, particularly within the 240-280nm range, exhibits potent germicidal properties, suitable for smaller water quantities, utilizing direct or sleeve-type UV disinfectors.
UV Disinfection
UV radiation between 200-280nm effectively kills pathogens without using chemicals, gaining prominence for its efficiency in controlling disease-causing agents.
Chemical Disinfection
Chemical disinfectants include chlorination, chloramines, chlorine dioxide, and ozone.
Chlorine Compounds
Chlorination, a widely adopted method, demonstrates strong, stable, and cost-effective germicidal properties, effectively used in water treatment. Chloramines, a derivative of chlorine and ammonia, preserve water taste and color with lower oxidative capacity but require complex procedures and higher concentrations.
Chlorine Dioxide
Regarded as the fourth-generation disinfectant, chlorine dioxide surpasses chlorine in many aspects, displaying better disinfection, taste removal, and lower carcinogenic byproducts. It’s less affected by water temperature and exhibits superior bactericidal effects on poor-quality water.
Ozone Disinfection
Ozone, an effective oxidizer, offers broad-spectrum microbial eradication. However, it lacks longevity, stability, and requires technical expertise for monitoring and control, predominantly utilized in bottled water production.
Below are some international standards for drinking water disinfection
The free chlorine index requirements are: contact time with water ≥ 30 minutes, factory water and terminal water limit ≤ 2 mg/L, factory water margin ≥ 0.3 mg/L, and terminal water margin ≥ 0.05 mg/L.
The total chlorine index requirements are: contact time with water ≥ 120 minutes, limit value of factory water and terminal water ≤ 3 mg/L, factory water surplus ≥ 0.5 mg/L, and terminal water surplus ≥ 0.05 mg/L.
The ozone index requirements are: contact time with water ≥ 12 minutes, factory water and terminal water limit ≤ 0.3 mg/L, terminal water residual ≥ 0.02 mg/L, if other collaborative disinfection methods are used, the disinfectant limit and residual The corresponding requirements should be met.
Chlorine dioxide index requirements are: contact time with water ≥ 30 minutes, factory water and terminal water limit ≤ 0.8 mg/L, factory water balance ≥ 0.1 mg/L, and terminal water balance ≥ 0.02 mg/L.
