By Walter Schajnoha, P.Eng.,
ProMinent Fluid
Controls Ltd.
Chlorination is the most popular means of water disinfection in North America. Two thirds of all communities which treat their water use some form of chlorination, with the majority of these having a population of less than 3,000 people. In comparison to any other form of disinfection, chlorine is ten times more popular. With the introduction of new regulations, the remaining communities that do not chlorinate will, in most cases, only add to the overall percentage when they are regulated to disinfect.
Alternative disinfection technologies are again attracting some interest for practical applications where chlorination is not providing the desired disinfecting effects or where disinfection by-products are a concern. Alternative disinfection technologies can also improve the aesthetic quality of the water through eliminating taste and odour problems, and enhance the performance of disinfection in the distribution system.
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| The ProMinent OZVa Ozone Generation System has a capacity of 5 to 720 grams of ozone per hour. |
Interestingly enough, when correlating the rate of THM (trihalomethane) occurrence above the maximum prescribed amount of 100 ppb (parts per billion), the majority of areas to have these concerns are municipal systems servicing populations of 3,000 people or fewer, with the only method of water treatment being chlorination. The source water in many of these areas is surface water and chlorine alone does not produce the by-product problems, which also require precursors in the form of organic materials.
When looking at systems with problems of disinfection by-products, first of all, the precursors that are present in the source water should be treated through coagulation and settling, or some form of filtration by some means. Another method would be to find an alternate source of superior quality. If this is not feasible, or does not prevent the formation of the by-products to the extent required, then it would be appropriate to look at the alternatives to chlorination that can be easily implemented to help supplement existing chlorination or replace it completely.
Ozone
One of the most powerful disinfectants that can be applied to water treatment is ozone. The use of ozone as a primary source of disinfection has been applied for many years, successfully removing many of the same waterborne microbiological contaminants as chlorine. Due to the higher strength of ozone, typical contact times and concentrations required are much lower than those for chlorine. Ozone also has the capability of inactivating Giardia and Cryptosporidium at reasonable contact times and concentrations.
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