Water Industry News

New York City studies use of UV light in drinking water


May 15, 2005

It's related to the bluish light that gives an artificial tan to beach fans in wintertime. Some brands of sunglasses promise to block it from harming your eyes. And one day it is likely to disinfect New York City's drinking water.

The city's Department of Environmental Protection is studying the use of ultraviolet light to disinfect most of the 1.3 billion gallons of water that residents of the five boroughs and Westchester County use each day. It will take at least four years before New Yorkers could actually drink the UV-treated water, provided DEP can get all the necessary approvals.

If all goes as the department hopes, New York's would be the largest application of UV disinfection in the world, significantly improving the city's tap water by rendering bacteria and microorganisms harmless so they cannot cause disease.

"UV provides a new level of disinfection that's simple and relatively inexpensive. It's great technology when you can make the water safer without adding chemicals, just a little ultraviolet light," said DEP deputy commissioner Michael Principe.

Going with the flow

Under the plan -- which has preliminary federal approval as part of a mandate to meet new Safe Drinking Water Act standards -- the $592-million price tag would be paid by residents of New York City and Westchester who get the water treated at a plant to be built on a 149-acre site everyone in nyc and about 1 million in west., which is most but not all residents.

DEP would connect the Catskill and Delaware aqueducts and funnel them into a new two-story, 160,000-square-foot building straddling two Westchester County towns.

There, the water -- up to 1.5 million gallons every minute -- would stream into one of 56 4-foot-wide pipes. Each pipe would be mounted with a "disinfection chamber," where up to 200 lamps would emit a constant stream of ultraviolet light into the water.

The system uses UV-C, one of three types of ultraviolet light. The other two types, UV-A and UV-B, can cause sunburns and eye damage and lead to skin cancer. The sun is the primary source of all three types, but UV-C, with the shortest wavelength, is reflected by the Earth's ozone layer and rarely reaches the surface.

An invisible power

UV-C would shine through the water for only a second or two before gravity draws the water back into the aqueducts and toward the city, where it reaches taps within a day. But in the brief time the water is exposed to the invisible light, crucial changes take place. Bacteria, viruses and microorganisms that exist naturally in surface water absorb UV-C into their cells. The light energy binds their DNA together so that it cannot be copied, effectively stopping the microorganisms from multiplying.

Principe, who oversees the city's water supply, estimates treatment with ultraviolet light will render harmless 99.9 percent of cryptosporidium. The small protozoa can in rare cases cause diarrhea and cramps in healthy people and lead to serious and long-lasting illness in people with weak immune systems. The city Health Department reported 125 cases of cryptosporidiosis in 2003, and people with HIV/AIDS accounted for 75 percent of those cases.

The germ-neutralizing power of UV also means the city can reduce its use of chlorine, which can harm the environment and create unwanted side effects.

"It's a physical process, rather than a chemical process," said Deborah Keesler, a DEP engineer overseeing the design of the treatment plant. "It doesn't change the odor, it doesn't change the appearance of the water, and you're not getting any of the byproducts you get with traditional disinfection."

Blueprint for change

DEP is in negotiations with the federal government to open the ultraviolet treatment plant in 2011, but the department must grapple with significant issues and concerns well before that time.

To build up enough water pressure to reach the treatment plant, the Catskill aqueduct will have to be shut down for nine months of the year, beginning in 2007. New York City and most upstate towns have alternate connections to bring them water, but that is not the case for Mount Pleasant, which relies entirely on the aqueduct.

"That's a very major issue that affects our town directly," said Mount Pleasant's supervisor, Robert Meehan.

DEP is weighing two options to bring Mount Pleasant drinking water during the shutdowns, with both creating temporary connections to the Delaware aqueduct, Keesler said. After consultations with town officials, DEP hopes to begin construction on one option next year.

Dr. Paul Lu, an environmental scientist at Jamaica's York College, voiced concern about the unprecedented scope of the project and the possibility of unforeseen complications. The same light energy that reduces microorganisms can change minerals and organic chemicals in the water in ways not yet understood, Lu said. Europeans have been using ultraviolet disinfection for years, but New York City's would be the largest application of the technology to date by far.

To address concerns, DEP will begin testing three chambers this summer in upstate Johnstown. The studies will help determine the right amount of UV to apply. DEP is also participating in research with a nonprofit foundation to see if microorganisms can repair themselves after UV treatment, Keesler said.

In addition, Keesler said the agency would closely monitor published research on UV-treated water, and the Environmental Protection Agency and the state Department of Health will inspect the operation annually.

Daniel Hendrick is a freelance writer.

Copyright 2005, Newsday, Inc.