September 2008, Vol. 20, No.9
Is UV a Universal Solution?
The article on ultraviolet irradiation for disinfection [“The Future Looks Bright,” June] is well done and a valuable contribution for guiding community water supply decision-making in the United States. However, it is lacking discussion of a key issue for water supply decision-makers in developing countries (DCs) on whether to choose chlorination — which leaves a residual in the distribution system — or to switch to ultraviolet irradiation or other methods (e.g., ozone) that do not produce residuals. A major problem in DCs is that distribution systems are not “tight” systems as in the United States, but commonly are replete with leaks and subject to pressure variations. Public health agencies, including the U.S. Public Health Service, over the past several decades have placed great emphasis on the importance of maintaining a disinfectant residual in the distribution system.
Should DC decision-makers continue to depend on chlorination, keeping in mind that disease rates are still very high in DCs for enteric diseases such as cholera, typhoid, and dysentery? The hazard of enteric disease is very great compared to that of pathogens that are not controlled by conventional chlorination.
Today’s international literature emphasizes disinfection of water supplies by nonchlorinating methods such as ultraviolet irradiation, as well as the cancer hazard of chlorination byproducts, which tend to get DC officials to abandon use of chlorination. It would be helpful if U.S. experts could lend their advice on this issue for guiding DC decision-making.
Harvey F. Ludwig
Consulting environmental engineer
North Samrong, Samutprakarn
The Future Looks Horizontal
The caption on page 44 [“The Future Looks Bright,” June] indicates, “Wastewater treatment plants typically use vertical open-channel ultraviolet systems.” Last check, Trojan Technologies, exclusively horizontal systems, has well over 4000 installations in North America. The entire installation base for Siemens “Sunlight Systems” is a couple hundred. Of the Siemens installations, all are not vertical. There are other manufacturers of vertical systems; however the number of vertical systems, regardless of manufacturer, are far outnumbered by horizontal. A conservative estimate would be approximately 10:1 horizontal to vertical.
Anthony P. Bilek
Drug Take-back Programs
It was great reading the article you had on drugs [“Taking Back the Drugs,” June]. A real challenge that we’ve seen in the industry is a failure to look for a proactive way to address issues raised by others. We saw it with biosolids, but it’s been [an issue] with drugs, pretreatment, nutrient treatment, etc. As an industry, we really do have to listen to the concerns of the public and look for ways that we can be part of the solution. I hope your proactive approach will be the basis for future articles to help our industry move forward.
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