By W. Kent Kise and Bak Srikanth
Summary: With acceptance by the USEPA of ultraviolet (UV) irradiation as a viable disinfection technology for treating drinking water, its attractiveness has grown in a number of quarters—bottled water as well as municipal and residential applications—because of its non-chemical effectiveness against a variety of bacteria and viruses.
Ultraviolet irradiation is a technology long proven effective in such diverse industries as pharmaceutical, semiconductor, power generation, food and beverage, cosmetics, aquaculture, health care for a variety of applications. While the most common application of UV irradiation in water treatment is disinfection, its powerful energy can also be harnessed for applications such as total organic carbon (TOC) reduction, ozone destruction and chlorine/chloramine elimination. Recent technological breakthroughs and new federal U.S. Environmental Protection Agency (USEPA) rules have now positioned UV to enter the Public Water Supply (PWS) disinfection market under which bottled water is regulated.
UV advantages for water
UV use in water treatment has several inherent advantages. UV irradiation doesn’t add anything such as undesirable color, odor, chemicals, taste or flavor, nor does it generate harmful by-products. It only imparts energy to the water stream in the form of UV light to accomplish the process of disinfection, TOC reduction or ozone destruction. It’s fast, effective, efficient and environmentally friendly.
Two different UV wavelengths are employed in water treatment, 254 nanometer (nm) and 185 nm. The 254-nm wavelength—also called “germicidal light” for its ability to destroy microorganisms—is employed in disinfection and ozone destruction applications. It penetrates the outer cell wall of the microorganism, passes through the cell body, reaches the DNA (deoxyribonucleic acid) and alters the genetic material (see Figure 1) so reproduction cannot occur. The microorganisms are thereby destroyed or rendered non-infectious in a non-chemical manner. The 254-nm wavelength can also destroy residual ozone present in a water stream. The 185 nm used in TOC reduction applications decomposes organic molecules through generation of hydroxyl free radicals. Hydroxyl radicals (OH)—formed in the natural decay of ozone (O3) to oxygen (O2)—are one of the most powerful oxidizing agents known. UV’s impact on ozone—which may also be produced at the 185-nm wavelength—is to speed up this degradation, very briefly creating a higher concentration of hydroxyl radicals that augment its disinfection capabilities.
Bottled water and UV
The bottled water industry has utilized UV technology for years for disinfection and ozone destruction applications. As the industry enjoys double-digit growth rates, new process technologies are emerging and existing technologies are being optimized. While the bottled water industry has utilized ozonation as the primary disinfection barrier, UV disinfection technology is rapidly gaining recognition and acceptance.
Historically, the bottled water industry has considered UV to be an acceptable technology for ozone destruction and secondary disinfection requirements. In addition, many states have prescriptive bottled water licensing requirements and regulatory codes that weren’t clear on UV use as the primary disinfectant since the USEPA hadn’t issued a formal “Best Available Technology” (BAT) notice on UV disinfection.
One of the principle challenges to acceptance of UV has been that Intensity Unit (IT) dose monitoring technologies weren’t accurate and were based on relative intensity vs. an actual NIST Standard. The National Institute of Standards and Technology (NIST) is a federal agency that works with industry to develop and apply technology, measurements and standards. The error in relative intensity monitors could be significant due to sensor location, quartz sleeves transmittance, sleeve and sensor fouling, and lamp intensity variability.
The USEPA recognition of UV as an approved disinfection technology was published in the May 10 issue of the Federal Register (see 40 CFR Parts 141 & 142) regarding National Primary Drinking Water Standards and the proposed Ground Water Rule. The new rule positions UV as a viable alternative to ozonation as noted in Table 1. Seventy-five percent of bottled water produced in the United States is spring water that, by FDA definitions, must be groundwater from a protected source. Among other things, the following represents some of UV’s breakthrough advancements that have supported the approval process:
- A 360° UV sensor incorporating real-time, absolute intensity measurement,
- More reliable lamps and ballasts,
- Validated lamp intensity, and
- NIST-calibrated UV sensor design.
Bottler technology approval
Bottled water quality standards at the federal level (see FYI: Bottled Water Rules) are based on USEPA Drinking Water Quality Standards (see www.epa.gov/ogwdw/standards.html). Once the USEPA establishes and promulgates drinking water standards for Public Water Supplies (PWSs), the U.S. Food and Drug Administration (FDA) must—by Congressional mandate—either accept or reject all standards and maximum contaminant levels (MCLs) within a prescribed time period. In addition to quality standards, the FDA requires bottled water to comply with established “Standards of Identity” in labeling and, as a regulated food product, it must be produced under current Good Manufacturing Practices (GMPs) as detailed in the Federal Register.
In addition to federal rules, bottled water must meet regulations for each and every state in which a particular brand is sold. With large scale distribution centers for grocery chains and superstores, this usually means obtaining licenses and permits for whole regions, if not the entire country. Each state has different rules and often state approval processes require the same comprehensive water source and water treatment approval documentation that any PWS would need to submit. In many states, the same state officials enforcing USEPA regulations review these approval documents when approving bottled water sources and bottled water treatment processes. Due to this permit review process, bottled water systems must meet the most rigorous of standards.
With the USEPA’s recent acceptance of the use of UV for disinfection, the state regulatory programs will have an established guideline for determining contact time (CT) values and applied IT dose for approving UV disinfection systems.
Definition of UV dosage
Mathematically, UV dosage can be expressed as a product of UV intensity and exposure (or residence) time. The most commonly used units of UV dosage are microwatt-seconds per square centimeter (mW-sec/cm2).
Other units in which UV dosage is expressed are in milliJoules per square centimeter—mJ/cm2. And, 1 mJ/cm2 = 1,000 mJ/cm2 = 1,000 mW-sec/cm2 since 1 J = 1 W-sec. This intensity × time formula is the basis behind the proper selection and sizing of UV equipment for a particular application.
UV system effectiveness
As for microbial and viral inactivation efficacy of UV systems, UV irradiation can effect a >4-log reduction even in not-so-clear feed water streams. The testing conducted by a beverage company shows almost a 5-log reduction in influent microbial levels even on a feed water stream exhibiting a UV transmission of only 51 percent (see Figure 1).
This fact is reinforced by the following data generated by a St. Louis-based microbiological laboratory from microbial challenge testing it carried out in 1997 using a UV unit. The resulting paper, published in the July/August 1995 issue of Ultrapure Water journal, demonstrates that UV technology is very effective and efficient at solving bacterial problems in real life, industrial applications. That paper described successful application of UV technology to solving acute microbiological problems faced by a Texaco co-generation plant located in Bakersfield, Calif.
UV water treatment systems designed for the drinking water treatment can also be used in other applications such as food and beverage, pharmaceutical, and any other industries where sanitary wetted parts must be used. The systems should—where possible—feature major design details including:
- Sanitary wetted components used in the treatment chamber,
- Simplicity in design,
- Advanced monitoring and control functions, including water temperature, flow and dosage display,
- NIST-traceable UV sensors and field calibration kits available for customer use,
- Expanded communications capability for remote access and control,
- Remote diagnosis capability, and
- New intelligent power supplies for driving the UV lamps.
UV monitoring & displays
Measuring absolute real-time UV intensity has gotten easier with recent advances that allow today’s UV treatment systems to calculate and display absolute UV intensity in milliwatt/cm2. This is a significant improvement over the relative intensity meter used in the older UV units. Sensors and display meters are calibrated against an NIST-traceable secondary standard.
An important tool that the customer often needs is testing equipment to periodically verify calibration of UV sensors and meters. NIST-traceable field calibration kits are now available that allow the user to perform such periodic calibration work, thus satisfying the requirements of regulatory agencies like the FDA.
- UV irradiation of drinking water fully satisfies the requirements of the USEPA Total Coliform Rule (see http://www.epa.gov/OGWDW/methods/tcr_tbl.html),
- UV disinfection meets or exceeds log reduction values for bacteriological requirements and the minimum 4-logs for viral population reduction;
- Recent advances in UV treatment system design, such as the use of sanitary wetted parts, makes it extremely ideal for drinking water applications. Advanced electronic control systems make UV intensity measurements (and hence, dosage calculations) an NIST-traceable activity—satisfying requirements of regulatory agencies such as the FDA.
- With the USEPA’s recent acceptance of UV for disinfection, state regulatory programs will have an established guideline for determining CT and applied IT dose requirements necessary for approving UV disinfection systems more broadly.
About the authors
W. Kent Kise is national technical manager for Nestle’s bottled water business, Perrier Group of America, and has 16 years experience in the food industry—having worked in addition for Campbell Soup, Hanover Brands and Clorox. A biology graduate of the Delaware Valley College of Science and Agriculture, he attended Saint John’s University’s MBA program. Kise serves as chairman elect of the IBWA Educational Committee, CBWA Technical Committee and the NSF Cryptosporidium Task Group. In addition to having launched four USEPA-certified laboratories, he’s assisted in rewriting bottled water state statutes for Florida, Pennsylvania, New York, Maryland and is currently working with Health Canada in developing National Division 12 Regulations. Kise can be contacted at (610) 530-5944 or email: http://firstname.lastname@example.org
Bak Srikanth is applications and project manager at Aquafine Corporation, a leading manufacturer of UV equipment for drinking water, wastewater and ultrapure water applications based in Valencia, Calif. He holds master’s degrees in chemical engineering and mathematics and a bachelor’s degree in chemical engineering. He has written, published and presented several papers on UV in water treatment. Bak’s memberships include the American Institute of Chemical Engineers, International Society for Pharmaceutical Engineering and American Water Works Association. Aquafine is the manufacturer of the Aqualogic system, an intelligent sensor/control technology featured on its new USD Series of sanitary UV equipment that’s dedicated to the pharmaceutical and food and beverage industries. Aquafine can be reached at (800) 423-3015 or (661) 257-4770, (661) 257-2489 (fax), email: email@example.com or website: http://www.aquafineuv.com