Chemical Disinfection

Chemical Disinfection

  • Application of liquid chemical agent to remove most pathogenic microorganisms
  • Examples of chemicals commonly used are:
    • Alcohol: rapidly bactericidal, tuberculocidal, fungicidal, virucidal
    • Chlorine: covers wide range of antimicrobial activity
    • Formaldehyde: bactericidal , tuberculocidal, fungicidal, virucidal, sporicidal
    • Glutaraldehyde: for high level disinfection of heat sensitive instruments

Disinfection kills or deactivates disease-causing organisms in a water supply and must provide a 99.9 percent inactivation of pathogens and enteric viruses to protect health and to comply with certain regulations. There are two steps of disinfection: primary step completes the optimum level of microorganism kill or inactivation, while secondary disinfection maintains a disinfectant residual in the finished water that avoids regrowth.

When joint with conventional treatment, such as coagulation, flocculation, sedimentation, and filtration, good results have been obtained. Groundwater systems that disinfect are encouraged to add filtration as they contain high level of iron and manganese. The effectiveness of disinfection is judged by analysing for an indicator organism (total coliform bacteria). This organism is harmless, its presence serves as an indicator that pathogens have survived.


Chlorine is inexpensive and been chosen to improve water taste and clarity while eliminating bacteria and viruses. However, pathogens are mostly unaffected by chlorine unless higher dosage used compare to those preferred for treatment purposes. The presence of these parasites may necessitate source water pre-treatment. Chlorine removes substances like manganese, iron, and hydrogen sulphide, which can taint water taste. Chlorination is flexible to fit any system size, relatively simple and treatment systems do not require extensive technical expertise.

Chlorination is done through usage of different product. Chlorine is kept as liquid in pressurized containers and injected as a gas directly into source water. As chlorine gas is a dangerous—even lethal—toxin, procedures must be cautiously controlled. Second option is treatment with a sodium hypochlorite solution. Although corrosive, but this solution is less risky and more user friendly than chlorine gas. The liquid is simply diluted and then mixed with source water to effect disinfection. Another alternative in solid form of disinfectant—calcium hypochlorite. It is corrosive and explosive when it comes into contact with organic materials. However, these powders, granules, and tablets may all be stored in bulk and used effectively for up to a year. In all of its forms, calcium hypochlorite dissolves easily in water.