WATER DISINFECTION METHODS, PART III
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OTHER AGENTS/ CHLORINATION
There are numerous other agents which have proved to be successful in destroying pathogens. Many of these must still be subjected to prolonged testing with regard to their physiological effect on man. Among these are certain surfactants and several types of surfactants which aid in destroying pathogens. The cationic detergents readily kill pathogens. Anionic detergents are only weakly effective in destroying pathogens. Because of their objectionable flavor and possible toxic effects, however, surfactants have not been seriously considered for treating drinking water.
Chlorine dioxide has unusually good germ killing power. Up to the present time no valid tests for its use have been developed because of the lack of means for determining low residual concentrations of this agent. Because it is such a strong oxidizing agent, a larger residual of chlorine dioxide would probably be needed than is the case with chlorine.
At present, chlorination in one form or another is regarded as the most effective disinfectant available for all general purposes. It has full acceptance of health authorities. Still there are certain factors which affect its ability to disinfect waters. These should always be kept in mind. They are:
- "Free" chlorine residuals are more effective than "combined" or "chloramine" residuals. Disinfection, regardless of the type of chlorine, becomes more effective with increased residuals
- A pH of 6.0 to 7.0 makes water a far more effective medium for chlorine as a disinfecting agent than to higher pH values of around 9.0 to 10.0.
- The effectiveness of disinfection increases with the amount of contact time available.
- The effectiveness of chlorine residuals increases with higher temperatures within the normal water temperature range.
- All types of organisms do not react in the same way under various conditions to chlorination.
- An increase in the chlorine demand of a water increases the amount of chlorine necessary to provide a satisfactory chlorine residual.
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