UV-based system optimizes water disinfection.

Researchers at the Georgia Institute of Technology are casting new light on the disinfection of water used in food processing. They have developed a nonthermal method that performs better and is less costly than existing techniques. The scientists have a pilot unit ready for testing in commercial facilities.

Like current technologies, the new Advanced Disinfection Technology System relies on ultraviolet (UV) radiation to eliminate molds, viruses and bacteria. But the new system handles water more efficiently and improves the overall effectiveness of the disinfection process.

In many cases, the lack of cost-effective disinfection means water at processing plants is used only once and then discarded. Even when a disinfection system is used, the process is not always effective. Most existing systems pump water through pipes lined with dozens of UV lamps. The lamps tend to foul quickly, reducing their effectiveness and requiring ongoing cleaning and replacement. UV light has little penetrating power--just about 1 inch--so used water must be run through long pipes to increase the likelihood that UV light will contact enough of the liquid to affect the microorganisms it carries.

The heart of the new advanced system is a pair of cylinders, one inside the other. The smaller cylinder rotates inside the stationary outer cylinder while water is pumped through the gap separating the two. Inside the gap, the cylinder rotation causes water to churn and tumble in a well-documented phenomenon called a Taylor vortex. It's actually a number of vortices, which mix water with light shining from four UV lamps embedded in the outside cylinder wall.

UV light penetrates the water thoroughly, so no additional cycles through the system are necessary. Fewer UV lights are required compared to conventional systems, thus saving energy. Even if the fluid absorbs radiation, which would normally limit light penetration and thus the effectiveness of conventional UV reactors, the vortex motion in the new design continuously exposes fresh fluid to the radiation surface. You bring the fluid in contact with just a few lamps in a repetitive basis. The vortex motion also keeps the lamps free of material buildup.

The device is mechanically simple. Its low rate of revolution--about 1 cycle per second--means no bearings or special seals are required. The process was designed for recycling water from fruit and vegetable washing at food-processing plants, but it could be applied in other industrial processes, including beverage and fruit juice processing, brewing and dairy processes.

Preliminary work with the new lab-scale UV disinfection device shows a reduction in the concentration of viable pathogens by a factor of more than 200, compared to existing technology with the same UV dosage. Further information. Larry Forney, School of Chemical Engineering, Georgia Institute of Technology, 311 Ferst Drive, NW, Atlanta, GA 30332; phone: [phone]; fax: Fax: [phone]; email: [e-mail].