UV stirring method may improve current disinfection techniques
06/01/2003
By MARK A. DESORBO
ATLANTA, GA.—Perhaps James Bond had it all wrong when he said, "shaken, not stirred."
Stirring, or mixing liquids at a specific revolution under ultraviolet radiation could prove to be a less costly and more effective process than existing disinfection techniques, according to researchers at the Georgia Institute of Technology.
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Project director Larry Forney and senior research engineer John Pierson are developing a method that they say will ensure that every particle in a liquid is equally exposed to the (UV) lamps, thus revolutionizing water treatment for a host of industries, including food and beverage processors.
The Food and Drug Administration (FDA), which in 2000 approved the use of UV in food processing environments, requires the disinfection of water used in food and beverage processing. It has extended requirement of its Hazard Analysis and Critical Control Point (HAACP) program to include juice processors, along with seafood, meat and poultry plants.
According to their research, Forney and Pierson say the lack of a cost-efficient process often means the water is used only once and that existing water treatment systems are not always effective.
Most systems pump water through a channel lined with a plethora of UV lamps, which tend to burn out quickly, reducing efficacy and requiring ongoing cleaning of residual build-up. Because UV light has little penetrating power—about an inch—water must run through long pipes to prolong UV exposure and kill microbiological contaminants.
"The more lamps, the bigger the headache. Sometimes, it's a Catch-22," says Forney, an associate professor of chemical engineering. "With this method, you don't need as many lamps."
At the heart of the method is a pair of cylinders. The smaller cylinder rotates inside the stationary outer cylinder, while water is pumped through the gap between the two containers.
Inside that gap, according to Forney and Pierson, the cylinder is rotated by a drill press at about one revolution per second, causing the fluid to churn in a phenomenon called a Taylor vortex.
"There are actually a number of vortices that mix the fluid past UV lamps that are attached to the outside cylinder wall," Forney says. "The fluid is forced up against the radiation. Imagine you're a pathogen; by the time you've gone from the bottom to the top, you've gone past the same lamps over and over again."
In their experiments, Forney and Pierson used fluids tainted with E. coli, and found 200 times more bacteria when they didn't rotate the cylinder. The faster the cylinder rotates, the more intense the disinfection. The motion of the vortex also keeps the lamps free of material buildup.
Originally designed for recycling water from fruit and vegetable washing, Forney's and Pierson's research indicates that the method could be used in other industrial processes.
"We think it could be useful for a number of water-treatment situations, ranging from storm-water runoff to bottle washing to certain industrial water recycling applications," Pierson says.
When it comes to water, Forney says there are two cleanup goals—make it clean enough to put back into the environment, and make it clean enough to consume. "The hope is to recycle it," Forney says. "Water is in short supply, and people do not realize that."
In the meantime, Forney and Pierson are continuing to explore other uses for their disinfection method, which can be applied to virtually anything—soft drinks, beer, orange juice and milk.
"We're in the process of using other kinds of fluids, such as orange juice with pulp, which has 500 to 600 times the viscosity of water," Forney says. "We're also in process of using apple and tomato juice, and anything that could pose a contamination problem. We're trying to get a feeling of how much these fluids absorb photons in the germicidal vortex wavelength."
The researchers are also developing devices to employ their method, including one that can spin at 5,000 revolutions per minute (rpm) and another to treat 500 gallons of water in an effort to control effluent and run-off problems on southern California beaches.
"I still don't know how to get it up to 500 gallons a minute," Forney says. "That's a lot of fluid. People build things that big for industry all the time, so I guess, hypothetically, it can be done."