07 August 2011 | SPL News | Research News

Cooling tower operators wanting to rely less on chemicals to treat water-based air conditioning systems may have an environmentally friendly alternative. A “green” nonchemical device (NCD) reduced bacterial growth, including Legionella (the bacterium that causes Legionnaires’ disease) according to a recent study by Special Pathogens Laboratory and the University of Pittsburgh. 

Cooling tower operators wanting to rely less on chemicals to treat water-based air conditioning systems may have an environmentally friendly alternative. A “green” nonchemical device (NCD) reduced bacterial growth, including Legionella (the bacterium that causes Legionnaires’ disease), according to a recent study by Special Pathogens Laboratory and the University of Pittsburgh.

The positive results come on the heels of a previous NCD study funded by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). Researchers, Janet E. Stout, PhD, Director of Special Pathogens Laboratory, and Radisav D. Vidic, PhD, the William Kepler Whiteford Professor and chair of Civil and Environmental Engineering at Pitt’s Swanson’s School of Engineering, tested five different types of NCDs from different manufacturers in model cooling towers.

The ASHRAE study found that none of the NCDs (pulsed electric-field, ultrasonic, hydrodynamic cavitation, magnetic) prevented bacteria from growing in the water-cooling systems. In fact, most produced the same or more bacteria as found in untreated water. In this recent study, Stout and Vidic tested a “green machine,” a mechanical water treatment device that relies on an electrolytic process to improve cooling tower performance (H-O-H Water Technology).

This NCD was evaluated using the same methodology as the ASHRAE study. The results showed that the device removed hardness and alkalinity from the cooling water, and was 100 times more effective in reducing bacteria in the model cooling tower compared to the control, and more effective than all of the previously tested NCDs.

 “The H-O-H device is the first device among the NCDs we’ve tested that showed a bactericidal effect,” says Stout, who is also a research associate professor in civil and environmental engineering at the Swanson school.  “The results also support our scientific method of using model cooling towers to evaluate water treatment devices.”

Heating and cooling systems constantly exposed to nature provide the perfect environment for microbial growth. When biofilm isn’t controlled, it clogs pipes and promotes the growth of scale, which results in poor performance, slowed cooling and energy loss.

Ineffective water treatment can allow dangerous bacteria like Legionella to flourish in the cooling systems of hospitals, commercial offices, and other water-cooled buildings. Numerous studies have shown that 40-60 percent of tested water systems contained Legionella.

Effective water treatment reduces the health risk caused by airborne bacterial emission. To safeguard the public, many organizations that promote industry best practices propose that cooling tower operators validate the effectiveness of water treatment by monitoring for disease causing bacteria.

According to Stout, “We observed a 1.9 log greater reduction in the total bacteria (HPC) counts in bulk water, and a 2.3 log reduction in Legionella. This data suggests that the H-O-H device may achieve bacterial control that could meet industry standards set by organizations like the Cooling Technology Institute and the Association of Water Technologies. This is a promising sign for cooling tower operators who are environmentally conscious. However, similar experiments on full-sized cooling systems are needed to validate our findings in the model system.”

While chemicals are most effective in controlling biofilm, corrosion, and deadly bacteria in evaporative air-conditioning systems, the results of this study suggest that a greener solution could become a reality.