| Popis: |
Among thousands of processes and the apparatus connected with them, the art of chlorination has become well established in the minds of the water works profession. Chlorination was started with the use of very crude equipment. Step by step this equipment was perfected. Vacuum types of equipment replaced pressure types. Automatic equipment which varied the flow of chlorine in proportion to the flow of water became available and offered a distinct advance over manual types. When chlorine is added to water a certain amount is absorbed by substances in the water in addition to that required for the killing of bacteria. If more chlorine has been added than is required for such absorption there will be an excess which is commonly termed "residual chlorine." This residual is used as a safety factor, and because this excess is easily measured by the use of orthotolidin, it has been generally accepted as a standard control in water purification work. The difference between chlorine applied and chlorine residual represents the chlorine demand of the water and this chlorine demand varies over wide limits. In the light of these facts, a desire arose for a perfect control system whereby chlorination was accomplished not only automatically in proportion to the flow of water, but in proportion to the chlorine demand, and with a certainty which would stand the test of legal cross questioning. It is apparent that such a control equipment would be a most useful tool in water works operation. Heretofore automatic equipment, although far better than manual, has not been the perfect control system. All variables involved in water treatment were not covered. Automatic equipment would compensate for changes in flow or pumpage, but |
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