Grace W.M. Lee

Removal of bioaerosols by the combination of a photocatalytic filter and negative air ions

Abstract This study focused on the investigation of the effectiveness of negative air ionization (NAI), photocatalytic oxidation (PCO), and the combination of NAI and PCO on the removal of aerosolized Escherichia coli, Candida famata, and λ vir phage under different relative humidity. The experiments were conducted with a stainless steel reactor equipped with a negative air ion generator, a photocatalytic filter, and two ultraviolet lamps with 365nm wavelength. The removal efficiency ( η ) , defined as one minus the ratio of the outlet concentration to the inlet concentration of the appropriate bioaerosol, was used to evaluate the effectiveness of the removal methods. The combination of NAI and PCO was the most efficient removal method for aerosolized E. coli ( η = 0.304 ± 0.06 – 0.364 ± 0.008 ) , C. famata ( η = 0.433 ± 0.08 – 0.598 ± 0.047 ) , and λ vir phage ( η = 0.689 ± 0.02 – 0.903 ± 0.06 ) . In this removal method, the contributions of NAI were higher than those of PCO for the removal of E. coli and C. famata; for the removal of λ virus phage the contributions of NAI and PCO were comparable NAI was the least efficient removal method for bioaerosols, and the removal efficiencies are: η = 0.175 ± 0.04 – 0.245 ± 0.03 for E. coli; η = 0.216 ± 0.007 – 0.297 ± 0.044 for C. famata; and η = 0.299 ± 0.12 – 0.384 ± 0.02 for λ vir phage.

Effectiveness of Photocatalytic Filter for Removing Volatile Organic Compounds in the Heating, Ventilation, and Air Conditioning System

Abstract Nowadays, the heating, ventilation, and air conditioning (HVAC) system has been an important facility for maintaining indoor air quality. However, the primary function of typical HVAC systems is to control the temperature and humidity of the supply air. Most indoor air pollutants, such as volatile organic compounds (VOCs), cannot be removed by typical HVAC systems. Thus, some air handling units for removing VOCs should be added in typical HVAC systems. Among all of the air cleaning techniques used to remove indoor VOCs, photocatalytic oxidation is an attractive alternative technique for indoor air purification and deodorization. The objective of this research is to investigate the VOC removal efficiency of the photocatalytic filter in a HVAC system. Toluene and formaldehyde were chosen as the target pollutants. The experiments were conducted in a stainless steel chamber equipped with a simplified HVAC system. A mechanical filter coated with Degussa P25 titania photocatalyst and two commercial photocatalytic filters were used as the photo-catalytic filters in this simplified HVAC system. The total air change rates were controlled at 0.5, 0.75, 1, 1.25, and 1.5 hr−1, and the relative humidity (RH) was controlled at 30%, 50%, and 70%. The ultraviolet lamp used was a 4-W, ultraviolet-C (central wavelength at 254 nm) strip light bulb. The first-order decay constant of toluene and form-aldehyde found in this study ranged from 0.381 to 1.01 hr−1 under different total air change rates, from 0.34 to 0.433 hr−1 under different RH, and from 0.381 to 0.433 hr−1 for different photocatalytic filters.

The Effect of Ozone on the Removal Effectiveness of Photocatalysis on Indoor Gaseous Biogenic Volatile Organic Compounds

Abstract In this study, the degradation of d-limonene by photocatalytic oxidation (PCO) (titanium dioxide [TiO2]/ultraviolet [UV]) and by the combination of PCO and ozone (O3) (TiO2/UV/O3) was investigated to evaluate the enhancement effect of O3. The degradation of d-limonene by UV/O3 was also investigated for comparison. The experiments were conducted with a quartz photoreactor under various gas flow rates (600–1600 mL min-1), d-limonene concentrations (0.5–9 parts per million [ppm]), and relative humidity (RH) (20–80%). The d-limonene removal efficiency of TiO2/UV/O3, TiO2/UV, and UV/O3 ranged from 62 to 99%, from 49 to 99%, and from 46 to 75%, respectively. The addition of 120-ppb O3 can enhance the d-limonene removal efficiency of PCO up to 12%. The apparent kinetic parameters (apparent rate constants, k apparent and Langmuir adsorption constants, K apparent) of TiO2/UV and TiO2/UV/O3 reactions obtained from fitting Langmuir–Hinshelwood models are TiO2/UV: k apparent = 1.45 × 10−3 ppm-m sec−1, K apparent = 0.34 ppm−1; TiO2/UV/O3: k apparent = 1.83 × 10−3 ppm-m sec−1, and K apparent = 0.35 ppm−1. When RH was higher than 40%, the residual intermediates yield rates of d-limonene of TiO2/UV/O3, TiO2/UV, and UV/O3 reactions ranged from 0.39 to 0.51 μmol carbon m−2 sec−1, 0.56 to 1.96 μmol carbon m−2 sec−1, and 157 to 177 μmol carbon m−3 sec−1, respectively. In the photocatalytic reaction experiments, the addition of 120-parts per billion (ppb) O3 can reduce the residual intermediates yield rates of d-limonene by up to 1.46 μmol carbon m−2 sec−1. These experimental results showed that O3 can enhance the effectiveness of photo-catalysis on the removal of d-limonene.

Electrostatic Enhancement of Collection Efficiency of the Fibrous Filter Pretreated with Ionic Surfactants

Abstract A study of the electrostatic enhancement of collection efficiency of filters pretreated with ionic surfactants has been carried out in controlled conditions with monodisperse aerosols. Cationic surfactant (dimethyl dioctadecylammonium bromide [DDAB]) and anionic surfactant (sodium oleate [SO]) were used to pretreat polypropylene fibrous filters as the positively and negatively charged filters, respectively. The effects of aerosol size, aerosol charge state, face velocity, aerosol type, and relative humidity (RH) were considered to elucidate their influence on the aerosol penetration. Results indicate that penetration through surfactant-pretreated filters was lower than that through untreated filters, and pretreatment of the filter with surfactant was observed not to affect the structure of the filter. The electrofieldmeter direct-measured the very clear electric field of filter when treating ionic surfactants. The results proved that pretreatment with surfactant caused filters to become charged. Comparing penetration through surfactant-pretreated filters with that through untreated filters with neutral aerosol, the penetration reduction factor of the surfactant-pretreated filters was in the range 1.3–2.2. Comparing aerosol penetration through the surfactant-pretreated filters with singly charged aerosol with that through untreated filters with uncharged aerosol indicates that the former decreases by a factor of 1.8–48.8. The surface fiber charges of the DDAB- and SO-pretreated filters were calculated to be 2.02 × 1−10 C/m and −1.53 × 10−10 C/m. Moreover, the aerosol penetrations through the surfactant-pretreated filters increased with the face velocity. Surfactant-pretreated filters performed better against solid aerosol than against liquid aerosol. RH has no effect on aerosol penetration through the surfactant-pretreated filters. Regression equations for Coulombic and dielectrophoretic single-fiber efficiencies in terms of the dimensionless parameters could be fitted by the experimental measurements of surfactant-pretreated filters in this work.