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Control of Legionella pneumophila in water by a paper filter impregnated with silver nanoparticles and UV-LED
Citation:
Woo, H., K. Schrantz, T. Dankovich, M. Rodgers, L. Boczek, AND H. Ryu. Control of Legionella pneumophila in water by a paper filter impregnated with silver nanoparticles and UV-LED. Presented at UNC Water Microbiology Conference 2019, Chapel Hill, NC, May 13 - 16, 2019.
Impact/Purpose:
The high prevalence of an opportunistic pathogen Legionella pneumophila in chlorinated premise plumbing systems has been widely reported, suggesting the need for additional protection to provide safer water. According to a recent EPA report, six candidate treatment technologies to control the risks from Legionella bacteria in premise plumbing systems have been commonly applied. However, all the treatment options are designed particularly for large building water systems. Most recently, microbicidal paper filters infused with silver ions were proposed as an inexpensive, effective treatment option. Besides the efficacy of silver ions in inactivating various waterborne microorganisms, the silver-doped filter has the potential for the development of a point-of-use (POU) device. The objective of this study was to investigate the inactivation efficacy of L. pneumophila using paper filters impregnated with silver nanoparticles. Also, we attempted to elucidate potential for a POU device development while integrating this filter with the emerging UV technology of light emitting diodes (LED).
Description:
Culturable cell numbers decreased by more than 90% (1-log inactivation) and 99.99% (4-log inactivation) after 2- and 10-minute incubation periods, respectively, whereas no significant physical removal of bacterial cells while filtering was observed. These results suggested that the main mechanism of microbial inactivation can be attributed to chemical disinfection by silver ions. The LED emitting at 285 nm slightly outperformed conventional low-pressure (LP) UV at 254 nm, resulting in approximately 1-log inactivation at a dose of 1.5 mJ/cm2 for the LED at 285 nm. Greater log inactivation of sequential treatments by silver ions and UV light when compared to the sum of two treatments individually suggested synergistic effects. Specifically, inactivation by silver ionization and post-UV exposure was determined to yield better efficacy than pre-UV exposure, as the former sequence resulted in about 0.5 log greater inactivation. The synergistic effects of treatments used in specific sequence (i.e., silver ionization and post-UV exposure) encourages further studies on its applicability for the development of a POU device to control premise plumbing pathogens.