SANITATION SERVICES - Disinfection Processes

The greatest risks to consumers of drinking water are pathogenic micro-organisms. Protection of water sources and treatment are of paramount importance and must never be compromised.

Waterborne pathogens can cause outbreaks of illness affecting a high proportion of the community and in extreme cases causing death. How much treatment is needed will depend on the level of protection of water supplies.

Completely protected groundwater may not require treatment, but all other supplies will require continuous disinfection. If water supplies are not completely protected from human and livestock waste, filtration is likely to be required.

Disinfection is the single process that has had the greatest impact on drinking water safety. There is clear evidence that the common adoption of chlorination of drinking water supplies in the 20th century was responsible for a substantial decrease in infectious diseases. Disinfection will kill all bacterial pathogens and greatly reduce numbers of viral and most protozoan pathogens.

Combined with protection of water sources from human and livestock waste, disinfection can ensure safe drinking water. In the absence of complete protection of source water, filtration is likely to be required to improve the removal of viruses and protozoa.

All waterborne disease outbreaks are avoidable. Pathogens can only cause disease and death in humans if water source protection, pathogen removal by disinfection or filtration, or integrity of distribution systems fail.

Disinfection

The most commonly used disinfection processes are chlorination and Chloramination, but ozone, ultraviolet irradiation and chlorine dioxide are also used.

These methods are very effective in killing bacteria and can be reasonably effective in inactivating viruses (depending on type) and many protozoa, including Giardia. Cryptosporidium is not inactivated by the concentrations of chlorine and chloramines that can be safely used in drinking water, and the effectiveness of ozone and chlorine dioxide is limited.

However, there is some evidence that ultraviolet light might be effective in inactivating Cryptosporidium, and those combinations of disinfectants can enhance inactivation.

Storage of water after disinfection and before supply to consumers can improve disinfection by increasing contact times. This can be particularly important for microorganisms, such as Giardia and viruses.

Providing a disinfectant residual throughout the distribution system can provide protection against contamination and limit re-growth problems; however, the issue of disinfection by-products needs to be considered. Chloramination has proved successful in controlling Naegleria Fowleri in water and sediments in long pipelines.