 technology to supplement its use of chlorine for drinking water disinfection.)
NEW YORK'S ASHOKAN RESERVOIR: New York City is turning to ultraviolet (UV) technology to supplement its use of chlorine for drinking water disinfection.
Image: © David Goehring
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The Big Apple wants to use the sun's power to provide clean drinking water for its nine million residents without adding more of the potentially harmful chlorine it uses as a disinfectant. More specifically, New York City officials are building a water disinfection facility some 30 miles (50 kilometers) north of Manhattan on a 153-acre (62-hectare) property in the Westchester County towns of Mount Pleasant and Greenburgh that will use ultraviolet (UV) light to destroy water-borne pathogens such as Escherichia coli, giardia, and cryptosporidium in reservoirs that serve city dwellers.
The city currently uses chlorine to disinfect its drinking water, which is piped in from New York State's Delaware County and Catskill watersheds about 100 miles (160 kilometers) north. But the U.S. Environmental Protection Agency (EPA)—empowered by the federal Safe Drinking Water Act (SDWA) of 1974 (and amended in 1986 and 1996) to set national safety standards—has urged communities since 1996 to cut back on chlorine, which produces harmful by-products when added to water, including trihalomethanes and haloacetic acids, known cancer-causing agents. The trick has been to reduce the chemical as much as possible without increasing the amount of disease-causing microorganisms in the water.
First proposed in 2003, the city got the ball rolling on the UV disinfection project shortly after the EPA in 2006 tightened restrictions on microbial pathogens allowed in drinking water. The UV facility, set to fire up in 2012, is expected to be the world's largest (pdf). When completed, it will consist of 56 40-million-gallon (151-million-liter) UV disinfection units designed to disinfect up to 2.4 billion gallons (nine billion liters) of water (pdf) per day.
All surface and ground water entering New York City's drinking water distribution system is currently treated with fluoride (pdf) to help prevent tooth decay as well as chlorine to kill deleterious microbes as designated by the New York State Sanitary Code and the SDWA.
The city in November 2005 commissioned Trojan Technologies, Inc., a wholly owned subsidiary of Danaher Corp. in Washington, D.C., to build a UV drinking water disinfection system to help comply with the EPA's rules.
"UV is a short wavelength that alters the DNA (genetic material) of the bacteria in the water, making it unable to reproduce," says Jason Cerny, Trojan's lead mechanical designer. "If you leave a pan of water out, UV rays from the light will clean it. We've just increased the scale, added a more efficient source of UV, and more power."
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11 Comments
Add CommentWhat about Ozon? It is easy to generate and does not need the regular cleaning the light bulbs need. If pure Oxygen is used as the feed for Ozone, nitrous oxides generated as bi-products can be eliminated.
Reply | Report Abuse | Link to this"The Big Apple wants to use the sun's power to provide clean drinking water" implies that the plant will be solar powered-but there's no indication of that in DEP's plan, or anywhere else in this article.
Reply | Report Abuse | Link to thisAlso, Jason Cerny says "If you leave a pan of water out, UV rays from the light will clean it. We've just increased the scale, added a more efficient source of UV, and more power." But, since they won't be using sunlight, they're opting for a less efficient source of UV. Strike two. If they really wanted efficient, they'd concentrate sunlight. Problem is that the sun doesn't shine every time someone in NYC flushes a toilet.
Let's see if the project could be solar-powered:
Average power consumed will be about 4MW, which would take a 30MW-capacity PV plant to run, which would fit in about 0.15 square kilometers, or 37 acres. That would fit in the 153-acre property.
UV radiation from energy derived from electricity produced from non renewable resources just exchanges one serious environmental impact for another (toxic chemicals to global warming). Not such a clever idea. Powered by PV cells? - a much better option.
Reply | Report Abuse | Link to thisAll projects of this nature need to consider the life cycle impacts of the technology. Chlorine produced from salt to chlorinate water, may have a lesser impact than the production of UV lights, operation of the lights, and disposal at the end of their life, together with climate change impacts of energy use.
Actually, people have done environmental assessments on UV technology versus other technologies like ozone and chlorine. For example, the City of Palo Alto did a study for their wastewater treatment plant and found UV to be a better solution. The energy required to transport all the raw materials for chorine production and energy used for chlorine production has a more negative impact on the environment. This is also true for ozone. Also, the trend to move away from chlorine is due to chlorine-resistant organisms like Cryptosporidium and Giardia. These organisms are easily inactivated by UV compared to chlorine.
Reply | Report Abuse | Link to thisI have to admit I am skeptical about the UV technique. Over ten years ago I worked for a company that tried to develop this technology. After years of research they gave it up because they found that, while the UV killed something like 99% of the types of microbes, it did not kill some of the most common and most harmful ones. According to the people I talked to, the use of UV did not even reduce the amount of chlorine needed. After carefully looking over the article, I notice that there is no claim anywhere that the need for chorine is eliminated or even reduced. I cannot help wondering if these installations actually do something better or if the companies making them just have good salespeople.
Reply | Report Abuse | Link to thisI found this article misleading and inaccurate. Having more than 40 years of wide ranging experience in drinking water quality, disinfection, and environmental health with the World Health Organization/Pan American Health Organization, Global Environmental Monitoring, and the U. S. Public Health Service, I feel qualified to comment.
Reply | Report Abuse | Link to thisThe article implies that chemicals should be done away with in water treatment. This simply is not feasible. They are essential for treatment of almost all surface water supplies and even some groundwater supplies.
Ultraviolet light (UV) is very effective in killing or inactivating waterborne pathogens but it cannot completely replace chlorination as a method of disinfecting water. The article fails to mention that the New York water system will be using a combination of UV and chlorine disinfection. EPA rules require systems utilizing surface water to maintain a sufficient residual level of chlorine to help protect treated water all the way to the tap. This is necessary for several reasons when primary disinfection is accomplished by ultraviolet light.
Even though the UV will kill pathogenic microbes passing through the UV unit, it has absolutely no effect on pathogens that enter the system subsequent to the UV exposure. There is considerable potential for pathogenic organisms to enter an aging water distribution system (such as serves New York) during drops in pressure or during ruptures and repairs, or even through clandestine cross connections to a contaminated water source.
Also UV does not preclude re-growth of organisms that might pass through the UV units due to weak or burned out UV lamps, build up of deposits on the quartz sleeves, or otherwise causes of inadequate exposure. I have personally investigated facilities that relied only upon UV disinfection and found pathogenic re-contamination or re-growth no more than a few meters past the UV units.
The article also implies that chlorination causes cancer. The reality is that it is high doses of some of the disinfection by products that might possibly cause cancer but when kept below the levels set by EPA standards, which have incorporated ample safety factors, there is very low risk that there will be such a deleterious effect. The levels should of course be kept as low as possible, but it is imperative to balance the risk of proven microbial infection with the theoretical risk of cancer when dealing with drinking water disinfection.
New York City should be commended for the combination of UV disinfection and chlorination to assure the safety of its drinking water. Fred M. Reiff
dear Mr. Reiff, you have good knowledge of UV and drinking water. pls dont mind if my question sound stupid to you. My qustion is "is it harmful in any respect to drink water directly from a water filter using UV for sterallizaion". i have heard that one should wait for few minutes and keep the water treated with UV in some shady place before drinking it. Riaz Layman
Reply | Report Abuse | Link to thisThe municipal swimming pool in Redding, Calif. uses UV to disinfect the water. It's a lovely experience to swim in this silky, non-smelly water.
Reply | Report Abuse | Link to thisthats bull about fluoride preventing tooth decay! That has never been proven and on the contrary people who live in countries whose water is not fluoridated they have healthier teeth and less cavities. for a scientific website you sure are misleading people with your statement about fluoride. im not even a scientist but have done enough research to know what you claim is bull. i do agree tho however that uv light is very helpful in removing the bacteria found in water.
Reply | Report Abuse | Link to thisfluoride does not prevent tooth decay! for a scientific web blog you sure are misleading people with that statement. in fact fluoride is the main ingredient in RAT POISON! It causes nuerilogical disorders, bone cancer and cancers of many kinds and organ faulure as it effects every organ thruout the entire body! want realistic proof. check this link for the material saftey data sheet and other factual info about fluoride here... http://www.infowars.com/poison-tap-water/
Reply | Report Abuse | Link to thisThe New York market, god of the New York Times, which, in turn is the bible of democracy in this city, espouse ideologues of Panama, which considered similar to that humans drink it: the to run of the fresh waters of the rivers of Panama, under the free, UV rays from the sun, 10 hours every day.
Reply | Report Abuse | Link to thisThat is, they consider boats spend by the Panama Canal, the only alternative that justifies the investment for retaining 2 billion gallons per day of water from rivers in Panama. For them, use as Larry report, for the people of Panama, or to generate electricity, is the same as leaving the water running to the sea.
No wonder, that this bible does not want to inform the world of the "OCEANOGENIC POWER" discovered in Panama by us, or, ¿Is it because this discovery is capable of removing the profitable news generated by the global economic crisis and climate change , by solving the world's thirst for energy and clean water?