Ultra-high temperature infrared disinfection of bioaerosols and relevant mechanisms

Previous studies have shown that bioaerosols can be inactivated in less than a second when exposed to temperatures of hundreds of degrees Celsius in an ultra-high temperature (UHT) process. Here, a new UHT system was developed to make UHT safer and more predictable, in which a heated porous cloth was oriented perpendicularly to the flow direction to produce more uniform flow temperatures. Infrared radiation, which can provide uniform heating for flat surfaces, was used to heat the cloth. Temperature measurements indicated that high temperatures were obtained at the cloth surface and that the downstream flow temperature was more axially uniform than radially/azimuthally uniform. For both Escherichia coli and MS2 virus test bioaerosols, the inactivations were found to be greater than 4.7 log for a cloth temperature of about 450 °C and residence time of 0.41 s. Results from gel electrophoresis showed that infrared-UHT treatment resulted in DNA damages to E. coli. Besides lab testing, the UHT system was found to reduce the concentration of outdoor culturable bacteria by 1-2 orders of magnitude at 210 °C and residence time of 0.1 s, but was less effective against fungi. On the other hand, SEM imaging and sampling downstream of the cloth revealed that the cloth emitted unidentified particles. The results of the work proved that this IR system - with its perpendicular orientation - can achieve high temperatures and high bioaerosol disinfection, and can be used to better relate temperature to inactivation. Furthermore, the ambient inactivation data, which are not available in literature, allow insights into the real-world applications of an UHT system.