Researchers design system to improve disinfection of water

Georgia Institute of Technology researchers have developed a better-performing, less costly method of disinfecting water used in food processing.

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

'We're creating a mixing pattern to ensure that every particle of water is equally exposed to the (UV) lamp,' said John Pierson, a senior research engineer at the Georgia Tech Research Institute and co-principal investigator. 'By doing a better job of mixing the water, you get better disinfection.'

Regulations in the US require the disinfection of water used in food processing before it can be reused. In many cases, the lack of cost-effective disinfection means water is used only once and then discarded. 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. More important, UV light has little penetrating power - just about an 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 micro-organisms it carries.

'Water right up against the lamp gets treated, and water farther away gets treated less - or maybe not treated at all,' explained Pierson, who is collaborating on the advanced disinfection system with Larry Forney, project director and an associate professor of chemical engineering at Georgia Tech.

The heart of the new advanced system is a pair of concentric cylinders. 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 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,' Forney explained. '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 build-up.

The device is mechanically simple. Its low rate of revolution - about one cycle per second - means no bearings or special seals are required, Forney added.

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.

'We think it could be useful for a number of water-treatment situations ranging from storm-water runoff to bottle washing to certain industrial-process water recycling applications,' Pierson said. 'It fits any application where you could use disinfected water rather than potable water, which would cut down on water use generally and conserve potable water in particular.'

The disinfection process developed by Forney and Pierson may find uses far beyond the project's original scope. Virtually anything that flows can run through the system, allowing for applications in the soft drink industry, brewing, dairy products and fruit juice processing. It would work for any kind of fluid for which there are concerns about the existence of pathogens, Forney explained. A non-thermal procedure, it could even supplant pasteurisation, which is expensive, changes the taste and consumes a lot of energy, he added.

A variation of the device could even be developed for swimming pools as a non-chemical alternative to keeping water germ-free.

'If you were able to pass pool water through a UV reactor successfully, it would feel like normal water,' Forney said. 'It would have no taste and wouldn't be irritating to your mouth, eyes and lungs.'

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, according to Carolyn Goodridge, a visiting postdoctoral fellow and member of the research team.

'We're also beginning to work with certain kinds of fluids, such as fruit juices, that absorb lots of radiation to see what effect our device has on the inactivation of pathogens in that kind of environment,' Forney added.