Effective drinking water disinfection

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The need for drinking water disinfection is as old as public water supply itself. Microbiological parameters for drinking water treatment include coliform bacteria and specific pathogenic species of bacteria, vira, and protozoan parasites. Although the objective is the same – to provide safe clean water – the methods used to do so are numerous. The most common methods for water disinfection are chemical ones. This article gives a brief overview of chlorine-based disinfection methods and the factors that can influence the choice of method.

“No single method can meet all needs,” explains chemist Dr Carsten Persner at Grundfos Alldos, who designs systems for chlorine gas dosing, and for electrolytic hypochlorite and chlorine dioxide generation. “Local regulations are probably the one factor that makes it most difficult to draw general conclusions and make recommendations. The next is availability of raw materials and the costs associated with each method – energy costs, chemical costs and so on,”

Chlorine continues to be the most prevalent method of disinfection worldwide. This can primarily be attributed to its long-proven track record as a reliable means of providing safe drinking water and to its relatively inexpensive price tag.

Chlorine works by forming hypochlorite (HClO) when dissolved in water. HClO is a fast-acting oxidant with a wide biocidal effect. It is highly effective at low concentrations that do not pose a danger to human health. The excellent sustained-release of chlorine is of particular benefit as it continues to disinfect a pipeline system over a relatively long period of time.

The challenges with chlorine gas disinfection are associated with the transport, storage and handling of the gas itself. In pressurized form it is stored onsite, requiring investment in a separate gas room and gas warning unit that can contain and deal with the gas in the event of a leak. Dr Persner: “Chlorine gas has to be handled with respect for the risks involved. Operators need to be trained in handling and safety procedures – both to prevent accidents and deal with the situation in the event one happens.”

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