Effectiveness of titanium dioxide photocatalyst filters and ultraviolet for controlling bioaerosols in HVAC system

摘要

This study investigated the effectiveness of titanium dioxide (TiO2) photocatalyst filter and ultraviolet (UV) for control of bioaerosols in a heating, ventilating, and air-conditioning (HVAC) system. The HVAC system was 80 cm×80 cm × 80 cm with a total air change rate (ACH) of 1 h~(-1) and a fresh ACH of 0.18 h~(-1). A Collison nebulizer generated the bioaerosols: Escherichia coli (E. coli) and yeast cells of Candida famata (C. famata) var. flareri. The culturable bioaerosols were collected and incubated through an Anderson one-stage sampler and culture agar for colony forming unit (CFU) counting. Two filters (Degussa-P25-TiO2-coated filter and commercial-TiO2-coated filter), two ultraviolet lamps (365 and 254 nm), and different relative humidity (30 and 60%) were conducted in the experiments for understanding the individual effectiveness of filtration mechanism, photocatalytic oxidation (PCO), and UV disinfect. Clean air delivery rate (CADR) was used for evaluating the effectiveness. The results indicated that the overall removal efficiency of E. coli was higher than that of yeast for different experimental conditions; for example, the CADR for E. coli (6.3 Lpm) was higher than that for yeast (2.5 Lpm) using Degussa-P25-TiO2-coated filter with 365nm UV at a relative humidity of 30%. The CADR for 254 and 365 nm were 23.2 and 6.3 Lpm, respectively, for Degussa-P25-TiO2-coated filter and 30% RH; the 254 nm UV enhanced the PCO obviously. The effect of relative humidity was unobvious for controlling the bioaerosols by TiO2-coated filter with UV irradiation. The CADR of Degussa-P25-TiO2-coated filter was slightly higher than that of commercial-TiO2-coated filter both for E. coli and yeast. In addition, the percentage of the effectiveness of the uncoated filter, Degussa-P25-TiO2 coating, PCO, and 254 nm UV disinfect was 3.3, 8.1, 39.0, and 49.6%, respectively, for E. coli (4.7, 9.5, 53.5, and 32.3% for yeast). However the PCO and 254 nm UV disinfect were the major mechanisms for controlling the bioaerosols.