Products and Services
Disinfection
General Summary
Disinfection is the last step in a water purification process. Water is disinfected to kill any pathogens passing through the system, which may include viruses, bacteria, including Escherichia coli, Campylobacter and Shigella, and protozoa, including Giardia lamblia and other cryptosporidia. Drinking or recycled water is required to maintain a residual disinfecting agent throughout the distribution system, in which water may remain for days before reaching its point of use. Following the introduction of any chemical disinfecting agent, the water is usually held in temporary storage - often called a contact tank or clear well to allow the disinfecting action to complete.
Applications
Potable water, industrial process water, recycling/reuse of waste or storm water, aquaculture.
Benefits and Features
- Chlorine disinfection - Chlorine is a strong oxidant that rapidly kills many harmful micro-organisms. Because chlorine is a toxic gas, there is a danger of a release associated with its use. This problem is avoided by the use of sodium hypochlorite, which is a relatively inexpensive solution that releases free chlorine when dissolved in water. Although chlorine is effective in killing bacteria, it has limited effectiveness against protozoa that form cysts in water (Giardia lamblia and Cryptosporidium, both of which are pathogenic).
- Ozone disinfection - O3 is an unstable molecule which readily gives up one atom of oxygen providing a powerful oxidizing agent which is toxic to most waterborne organisms. It is a very strong, broad spectrum disinfectant that is widely used in Europe. It is an effective method to inactivate harmful protozoa that form cysts. It also works well against almost all other pathogens. Ozonation does not provide residual disinfectant.
- UV Disinfection - Ultraviolet light is very effective at inactivating cysts, as long as the water has a low level of colour so the UV can pass through without being absorbed. The main disadvantage to the use of UV radiation is that, like ozone treatment, it leaves no residual disinfectant in the water.
- Because neither ozone nor UV radiation leave a residual disinfectant in the water, it is sometimes necessary to add a residual disinfectant after they are used.