Volume 16 | Number 2 | Summer 2004

Environmental Issue

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Innovative UV Disinfection System Proves It Can Tackle Pathogen Control in Turbid Liquid Streams

UV Disinfection System
Senior Research Engineer John Pierson spearheads the continued development of Georgia Tech’s advanced UV disinfection technology.

Georgia Tech’s Taylor vortex-based advanced UV (ultraviolet) disinfection system has successfully demonstrated it can be used as a treatment option for vegetable rinse water reuse applications. Over the past year, researchers have also demonstrated its potential effectiveness at inactivating pathogens in more turbid liquid streams. In particular, the research team concentrated on liquid streams that would not be amenable to advanced oxidation methods such as ozone or peroxide. Much of the recent work centered on food safety applications, specifically the disinfection of juices, marinades, and unfiltered chiller water.

“Initially, we tested apple and grape juice disinfection because of a market need and because we saw those liquids had properties similar to marinations. Our results are important not only for juice manufacturers, but also the poultry industry,” comments John Pierson, senior research engineer.

In fact, according to Pierson, preliminary laboratory results indicate that the visual opaqueness of these liquids can be overcome by using the Taylor vortex-based UV system. To truly appreciate the significance of this finding, one must understand the Taylor vortex concept as compared to conventional UV disinfection technology.

Germicidal UV light is commonly used as a disinfectant for the targeted treatment of pathogens; however, many chemical and physical compounds contained in a liquid potentially absorb the UV energy. As a result, liquid streams possess a distinctive characteristic known as absorption coefficient. The more the liquid absorbs UV light, the less depth that UV light can penetrate.

Figure 1
Figure 1. Water has a UV penetration depth potential that is approximately 200 times greater than that for marinade and twice that of unfiltered chiller water.

UV disinfection system manufacturers typically increase the number or intensity of the lamps to compensate, but this can lead to product heating and potential product quality problems. Greater liquid turbulence is sometimes introduced to help with UV dosage penetration, but delivering a uniform UV dosage is still a problem.

The unique design of Georgia Tech’s UV disinfection system addresses those challenges. Unlike conventional UV disinfection technology, the Georgia Tech system utilizes the Taylor vortex mixing principle to produce outward moving vortices. The device that achieves this is comprised of a solid rotating cylinder (rotor) that is turned within an open cylinder (stator). The gap between the rotor and inner stator wall is significantly smaller than the radius of the rotor. As a result, the fluid in the gap is moved uniformly toward the outer wall such that any bacteria in the fluid are moved outward as well. The system’s UV lamps, which are placed around a transparent quartz stator, ensure that UV exposure is maximized. In a nutshell, the Taylor vortex design continuously pushes the liquid to the quartz stator surface where it exposes any bacteria present to a uniform dosage of radiation, thus providing much greater inactivation efficiency.

This is significant when focused on the challenge facing conventional UV technologies. Figure 1 shows that water has a UV penetration depth potential that is approximately 200 times greater than that for marinade and twice that of unfiltered chiller water.

According to Pierson, the research team’s preliminary work, which has been accepted for publication in the Journal of Food Protection, shows a 5-log removal of E. coli (ATTC 15597) from apple and grape juice concentrate using the Taylor vortex as compared to a 2-log removal with no Taylor vortex rotation. The research team found apple juice to be somewhat inhibited relative to grape juice, even though apple juice has a greater penetration depth. As a result, explains Pierson, more experiments are needed to address apple juice constituents that may absorb the radiation dosage.

While unfiltered chiller water overflow has a greater penetration depth than either apple or grape juice, both dissolved and suspended solids from fat, protein, and other materials compound the dosage absorption equation by shielding some pathogens from germicidal UV light. For chiller water disinfection to work more effectively without filtration, Pierson notes that researchers are working to ensure the inactivation of pathogens attached to solid material in liquid streams.

Over the course of this year’s work, researchers discovered that the optimum cylinder rotation rates previously identified for water and juices without suspended solids were higher than those providing the best inactivation efficiencies for unfiltered chiller water. They also found the data spread for duplicate points was greater, which, as Pierson explains, means they will have to include solids analysis for each sample to rule out testing method errors. However, he adds the research team did see a 4-log removal with 284 mJ/cm2, which represented a 45-second exposure.

“ We are cautiously optimistic we can enhance our Taylor vortex operating protocol or design for unfiltered chiller water disinfection. At the same time, we are planning to launch a study on using the system to treat storm water runoff,” adds Pierson.