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WEFTEC®.06 On-Site Sodium Hypochlorite Generation Applications - Sodium Hypochlorite systems have been used in drinking water and waste water applications since their early development. Electrolytic cell development in the early 1970’s started the search for plants where this radically new concept would be accepted. The result was to sell a few drinking water and wastewater plants in the United States with entrepreneurial managers operational systems in the late 1970’s. These systems were successful in proving on-site systems as a viable alternative to chlorine gas for water treatment plants. The most severe obstacle was the cost of chlorine gas through out the United States. Plant users could not operate this equipment cost effectively when compared to the cost of chlorine gas. Presently, water utilities are converting to on-site generation for small to moderate plants particularly where plant upgrades are taking place. This changeover continues to evolve slowly as the technology becomes more accepted and as the advantages of small systems installed at remote well sites or centralized in housing developments become evident. It is also useful to note that approximately 80% of all drinking water systems in the United States require less than 500 pounds of chlorine per day. On-Site Sodium Hypochlorite System Design Considerations On-site sodium hypochlorite systems are typically used for disinfection of drinking water (wells or surface water), wastewater disinfection, cooling water applications or for food processing operations. With very few exceptions, most of these sites are indoor installations where climate control is not a design issue. Low water temperature or pressure can be a problem for hypochlorite systems. Sites with feed water colder than 60o F (15oC) may require one to warm the water to help prevent premature electrode coating failure. Another problem is caused by water colder than 40oF (5oC) is a reduction in cell performance efficiency. Here again one must increase the feed water temperature to maximize performance. Low water pressure requires the installation of a booster pump in the water feed system. Pressures below 40 psig are not normally acceptable for reliable hypochlorite system operation. To get the most efficient operation from on-site electrolyzer cells, the cell feed temperature and the temperature rise through the cell are best controlled between 60o F (15oC) and 95oF (35oC). Having maintained the feed water temperature and cell temperature rise in this range one should also reduce the sodium chlorate in the product caused by chemical inefficiency reactions and localized electrode reactions. It may be difficult to control inlet water temperature on small remote sites. Therefore, is usually applied to sites of over 50 pounds per day. Larger systems usually include tanks of several thousand gallons (greater than 10 cubic meters) in the hypochlorite generation system. Excessive sun and increased temperature in the product hypochlorite storage tanks will cause accelerated degradation due to increased temperature and UV-light exposure. Fiberglass tanks have a less severe degradation problem than translucent tanks because they tanks are protected by an exterior white gel coat. Also, proper anchoring of larger tanks is essential to account for high wind loads. Copyright ©2006 Water Environment Foundation. All Rights Reserved 6348PDF Image | On-Site Sodium Hypochlorite Generation
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