The New UV
Ultraviolet (UV) technology is used in water and beverage bottling, generally under the classification of “polisher,” as a secondary or tertiary treatment. It is accepted for positive effects in reducing microbes without chemicals or disinfection byproducts; however, because it has no residual or dipstick measurement, laboratory effectiveness was extrapolated to the plant with few specific standards. During the late 1990s, it was discovered that UV could inactivate Cryptosporidium at low doses, and concern about disinfection byproducts spurred studies on what design and operational factors impacted UV effectiveness. As an instantaneous process, dose distribution is key because an overdose in one area cannot compensate for an underdose in another.
The U.S. Environmental Protection Agency (EPA) reacted to these developments by investing nearly six years studying how to regulate and use UV. Working together, environmentalists, engineers, microbiologists, chemists, municipal water professionals, regulators and public health officials examined the European validation testing processes. Based on a dose measuring process called biodosimetry, Germans validated a single disinfection dose number—40—for all operating conditions based on “the Germicidal wavelength,” 253.7. They chartered extensive studies and eventually proved that uneven dose distribution, UV transmittance of the water and sensor performance play critical roles in reactor effectiveness and might not show up in a simple validation protocol, especially if there was no operational follow-through.
The EPA’s stakeholder input process developed a consensus around UV—a key step toward fitting it into a U.S. drinking water framework. It was decided that:
- UV is a powerful disinfectant when engineered properly;
- Measuring and validating UV dose requires detailed protocols and standards that consider hydraulics, fouling and nonuniform lamp aging and mercury lamp breakage;
- A single wavelength standard is the easiest to use but not all organisms respond uniformly to monochromatic UV; and
- To protect public health, operational and maintenance standards must be established.
This consensus became the foundation of the EPA’s regulatory scheme. Because UV could be a solution to Cryptosporidium and Giardia as well as a nonchemical, no-disinfection-byproduct alternative to chlorine and ozone, the EPA protocol validates more than one dose level and verifies operational integrity on a continuous basis.
The final UV Disinfection Guidance Manual (Nov. 2006) requires 95% of the water delivered to customers be disinfected to the validated dose based on a thorough full-scale validation, and that monthly reports comply with monitoring, reporting and sensor calibration requirements and proper system maintenance.
All aspects—including lamp aging, fouling patters, sensor drift and dose distribution—are covered by the detailed EPA validation protocol and regulatory monitoring regime. The EPA provides both a Setpoint Approach, which alarms when a set point is not achieved, and a Calculated Dose Approach, which provides a specific dose number at any point. There are two aspects:
- Biodosimetry determines the actual reactor dose based on a microbe challenge test. A validation factor discounts the dose for various types of uncertainty associated with the specific reactor characteristics and operations. This process determines the permitted operational envelope of UVT, flow and UV intensity.
- Technical and functional testing of the components, which may trigger additional discounting factors.
Thus, when the EPA says a reactor must produce a specific dose to achieve a particular disinfection credit (e.g., a dose of 12 mJ/cm2 for 3-log Crypto treatment), it means the dose after all discount factors have been applied.
The EPA grandfathers the German validated dose of 40 mJ/cm2 to be equivalent to 3-log Crypto treatment (EPA validated dose of 12 mJ/cm2). The EPA only allows virus credit for reactors validated under the EPA protocol that achieves the required dose. So while the Europeans set their dose of 40 mJ/cm2 to include some general safety factors, the EPA dose calculation uses specific validation factors to discount an individual reactor based on performance.
Innovation & the Industry
While the EPA validation has spurred technological developments and enhanced knowledge of the reliability and effectiveness of UV systems, the traditional “it-can’t-hurt” attitude has yet to be replaced by strong standards in the bottling industries.
A more knowledgeable market has spurred the development of systems that take dose distribution seriously, such as computational fluid dynamics modeling for designing reactors, dyed microspheres to measure dose distribution and hydro-optic disinfection, which provides uniform dose distribution. The focus on dose and reactor control spurred innovations in software and user interface as well.
Recently validated based on the final EPA protocol, hydro-optic disinfection by Atlantium Technologies exemplifies this innovation. It uses a quartz reactor and fiber-optic technology to achieve a high log kill with medium-pressure mercury lights out of the water so there is no risk of mercury. The inlet/outlet bells protect the hydraulic integrity of the chamber and assure that upstream or downstream hydraulic changes do not compromise reactor effectiveness. An ultrasonic cleaning system shakes any potential deposits loose, keeping the quartz surfaces clean.
One key area of innovation has been UV controls. Several manufacturers had new software versions to monitor the UV disinfection process. Hydro-optic UV disinfection provides specifics about the dose, flow and UVT on a real-time basis. It obtains this data from two separate sensors per lamp, stores it in an extensive database and uses it to generate EPA reports.
Research and innovation in UV disinfection means validated UV disinfection systems with good dose controls, internal UVT monitors and uniform dose distribution that protects the entire water treatment process and helps water bottling and beverage plants reduce chemical disinfectants. Even the traditional uses of UV, such as after reverse osmosis and for recirculating finished water storage tanks, now can get improved log reductions and serious microbial control.
Bottlers who maintain a bulk chlorinated water supply for batching can consider eliminating the use of chlorine and instead use a properly sized EPA-validated UV system. UV can be added in-line prior to the batch tank with a continual UV recirculation loop. By eliminating the chlorine from the process, the bottler also reduces the threat of THMs in the finished product as well as maintenance issues associated with the use of granular activated carbon (GAC), often used to remove chlorine. Whether it is the chlorine trickle-through, a serious breakthrough or carbon filter traps that become a new microbial haven, GAC towers can be susceptible to contamination. UV can provide an alternative, or where the GAC is removing many contaminants, a barrier against microbial risks to process and product water.
The use of UV is especially beneficial for bottling sensitive beverages. The use of medium-pressure UV on the rinse water supply will reduce the risk of algae contamination and control Pseudomonas, Crypto, Giardia and other microbes that are not as susceptible to chlorine, and it provides better overall microbial integrity of the rinse water.