The Basics Of UV

Disinfection with light is effective against a wide range of water-borne pathogens. It also leaves no potentially harmful byproducts.

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The operator of a small water system asked about an alternative disinfectant to chlorine. The community was interested in an economically feasible choice because the U.S. EPA Phase 2 Disinfectant and Disinfection Byproducts Rule was about to take effect.

The aquifer in southeast coastal Georgia and northern Florida has elevated organics levels, and chlorine disinfection can lead to the formation of trihalomethane contamination. We told the operator that increasingly, over the past decade, it has been challenging to produce safe, clean drinking water.

Outbreaks of water-borne diseases in the United States and Canada have made people aware that water contaminated with microorganisms can cause serious illness or even death. The challenges posed by contaminated water are more common in the developing world, but there are growing indications that industrialized countries have not managed their water resources properly.

We also noted that confidence in the ability to protect human health from contaminated drinking water has been eroded by questions about the safety and effectiveness of traditional chlorine disinfection.

The Role Of UV

Chlorine-resistant pathogens and concerns about potentially cancer-causing disinfection byproducts (DBPs) from chlorine treatment have led to new EPA guidelines that require municipalities to eliminate or reduce chlorine usage. We pointed out that ultraviolet (UV) light disinfection has become an answer.

UV treatment has been used in Europe and North America for decades. The first applications were in France starting in 1910. UV technology is a highly effective, cost-efficient and proven way to destroy micropollutants and microorganisms. It has earned the confidence of thousands of municipalities for disinfecting wastewater, drinking water and industrial process waters.

The UV light spectrum lies between the shortest wavelength of light visible to the human eye, and X-rays, which of course are invisible. Specific wavelengths within this band of the light spectrum are characterized as germicidal. Water treatment systems use a UV light source with a protective covering (usually a watertight quartz sleeve) immersed in water to be treated.

The UV rays emitted by the lamp inactivate harmful microorganisms and parasites. As the water rushes by the lamps, microorganisms are exposed to a lethal dose of UV energy. The rays alter the DNA of parasites, yeasts, molds, algae, bacteria and viruses, so that even though they are technically still alive, they cannot reproduce, are powerless to infect a host and are considered inactivated. The process has a 4-log effectiveness, which means it destroys 99.99 percent of the target organisms.

Clear Benefits

Among its advantages, UV disinfection is safe and environmentally friendly — there are no chemicals for system operators to handle and no potential for chemical releases to the environment. UV leaves no smell or taste in the treated water, and in fact the process can improve the water’s taste by destroying organic contaminants.

We told the community’s operator that UV treatment should be used in combination with other forms of disinfection and filtration. UV systems in drinking water are most commonly used as a secondary treatment process and as a primary disinfectant. They are not intended to treat water that is visually contaminated, and they cannot convert wastewater to safe, potable water.

UV technology is endorsed by the EPA. It destroys bacteria such as E. coli, viruses like those that cause hepatitis and polio, and virtually all other waterborne pathogens. This includes Cryptosporidium and Giardia parasites, which are resistant to chlorine disinfection. UV also eliminates harmful micropollutants such as herbicides and pesticides. It works at least 20 times as fast as chlorine and is more cost-effective.

Future Potential

Looking ahead, solar water disinfection has been comprehensively researched in Switzerland, and scientists have proven that natural sunlight can effectively treat small volumes of water inexpensively. In this process, contaminated water is poured into transparent plastic bottles, and the bottles of water are exposed to full sunlight for six hours.

The sunlight treats the contaminated water through two synergetic pathways. First, UV-A radiation damages the DNA of organisms present in the water, and second, the process raises the water’s temperature, damaging the proteins in pathogenic organisms. If the water’s temperature rises above 120 degrees F, the disinfection process occurs three times faster.

About The Author

John Rowe, Ph.D., is a professor of water resources at Okefenokee Technical College in Waycross, Ga. He can be reached at


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