Kuo-Pin Yu

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 antifungal efficacy of nano-metals supported TiO2 and ozone on the resistant Aspergillus niger spore

Recently, antimicrobial efficacy of nano-metals has been extensively investigated. However, most of the related studies focused on the bactericidal effectiveness. Molds, especially their spores, are more resistant than bacteria, and can build a high concentration in houses due to dampness. Therefore, a comprehensive evaluation of the antifungal effectiveness of nano-metals is necessary. In this study, the nano-metals (Ag, Cu and Ni) supported catalysts were successfully prepared by the incipient wetness impregnation method, while the titanium dioxide (Degussa (Evonik) P25) nanoparticle was served as the support. The antifungal experiments of Aspergillus niger spores were conducted on two surfaces (quartz and putty) in the darkness with and without ozone exposure, respectively. The critical Ag concentration to inhibit the germination and growth of A. niger spores of 5 wt% nano Ag catalyst was 65 mg/mL, lower than several cases in previous studies. The inactivation rate constants (k) of A. niger spores on nano-metals supported catalysts in the presence of ozone (k=0.475-0.966 h(-1)) were much higher than those in the absence of ozone (k=0.001-0.268 h(-1)). However, on the surface of TiO₂ particles, no antifungal effect was observed until 6-h exposure to ozone. Consequently, ozone has a synergetic effect on nano-metals antifungal efficacy.

Aerosol penetration properties of an electret filter with submicron aerosols with various operating factors.

This study was undertaken to determine the effects of using an electret filter on aerosol penetration. Various factors, including particle size (0.05 to 0.5 μ m), aerosol charge state (neutral and single charge), face velocity (0.1, 0.3, 0.5 and 1.0 m/s), and relative humidity (RH 30% and RH 70%), were examined to assess their effects on aerosol collection characteristics. The results presented here demonstrate that the electric fields of the electret and discharged filter were −1.53 × 104 and −1.3 × 102 (V/m). The penetration through the electret filter with singly charged aerosol and neutral aerosol ranged from 0.4% to 13% and 14% to 29%, respectively. According to these results, the coulombic capture force was dominant for the smaller aerosol and the dielectrophoretic capture mechanism was considered important for the larger aerosol. The level of penetration through the electret filter increased with increasing face velocity and relative humidity. The temperature did not affect the penetration through the electret. Furthermore, from the regression analysis conducted during the operating conditions of this work, the aerosol charge was shown to exert the greatest influence on aerosol penetration.

Enhancement effect of relative humidity on the formation and regional respiratory deposition of secondary organic aerosol

In this study, we investigated the effect of relative humidity (RH) on the formation of secondary organic aerosol (SOA) generated from the ozonolysis of d-limonene in an environmental chamber. The mass yield and the number concentration of SOA increased seven and eight times, respectively, when the RH increased from 18% to 82%. The measured total loss rates (apparent loss rates) of the number and mass concentration of SOA in the chamber ranged from 1.70 to 1.77 h(-1) and from 2.51 to 2.61 h(-1), respectively, at a controlled ventilation rate of 0.72±0.04 h(-1). The wall-deposition-loss-rate coefficient observed (1.00±0.02 h(-1)) was approximate to the estimated value based on Zhao and Wus model which includes the factors of turbulence, Brownian diffusion, turbophoresis and surface roughness. According to the ICRP (International Commission on Radiological Protection) model, the inhaled SOA particles are deposited primarily in the alveoli of the lung. The integrated alveolar deposited dose of the mass (surface area) of SOA over 3h accounted for 74.0-74.8% (74.3-74.9%) of the total deposited dose at the investigated RH. Raising the RH resulted in the growth of SOA particle sizes and increment of the deposition dose but did not cause significant changes in the ratio of regional to the total respiratory deposition of SOA.

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.

Enhanced antimicrobial efficacy of thermal-reduced silver nanoparticles supported by titanium dioxide

The antimicrobial efficacy of silver nanoparticles (AgNPs) is influenced by many factors, including the particle size, AgNP oxidation state and support materials. In this study, AgNPs are synthesized and supported by two types of TiO2 powders (P25 and Merck TiO2) using two heat-treatment temperatures (120 and 200°C). The formation of well-dispersed AgNPs with diameters ranging from 3.2 to 5.7nm was confirmed using transmission electron microscopy. X-ray photoelectron spectroscopy and X-ray diffraction indicated that the majority of the AgNPs were reduced from Ag+ to Ag0 at 200°C. The AgNP antimicrobial activity was determined by the zone of inhibition against three fungi, A. niger, P. spinulosum and S. chartarum, and two bacteria, E. coli (Gram-negative) and S. epidermidis (Gram-positive). The antimicrobial activity of metallic AgNPs was more pronounced than that of silver nitrate and some antimicrobial drugs. The AgNPs exhibited optimal antimicrobial efficacy when the AgNP dispersion on the surface of TiO2 was in the region between 0.2 and 0.7μg-Ag/m2. The minimum (critical) AgNP concentrations needed to inhibit the growth of bacteria (E. coli) and fungi (A. niger) were 13.48 and 25.4μg/mL, respectively. The results indicate that AgNPs/TiO2 nanocomposites are a promising disinfectant against both bacteria and fungi.

Enhancement of the deposition of ultrafine secondary organic aerosols by the negative air ion and the effect of relative humidity.

Deposition is an important process for the removal of aerosol particles. Negative air ion (NAI) generators can charge the ultrafine airborne particles and enhance their deposition rate. However, many NAI generators may also emit ozone and increase the concentration of particles in the presence of biogenic volatile organic compounds owing to the secondary organic aerosol (SOA) production. To validate the effectiveness of NAI generator, the authors investigated the enhancement effect of an NAI generator on the deposition of the ultrafine SOAs generated from the ozonolysis of d-limonene in a test chamber under controlled ventilation rate and relative humidity (RH). The experimental results demonstrated that compared with other effects, including the gravity, particle eddy diffusion, and the Brownian diffusion, the effect of NAIs is the most dominate one on the deposition of SOA particles onto the wall surface in the near-wall region (<1 cm away from the wall). According to these experiments, the tested NAI generator could efficiently enhance the deposition rate by an enhancement factor ranging from 8.17 ± 0.38 to 25.3 ± 1.1, with a low ozone production rate. This NAI generator had better performance on the deposition of the SOAs with smaller particle sizes and it performed even better under higher RH. The enhancement effect of the NAI generator was related to its high NAI production and electric field strength. Implications: This study investigated a novel technique of negative air ion (NAI) generator that can enhance the precipitation of nano-scale secondary organic aerosol (SOA). The tested NAI generator can significantly improve the deposition rate of SOA with an enhancement factor of about 8.17 ± 0.38 to 25.3 ± 1.1. The enhancement factor rose when relative humidity increased.

Removal of indoor α-pinene with a fiber optic illuminated honeycomb monolith photocatalytic reactor

This study was undertaken to investigate the influencing factors including gas flow rate, inlet α-pinene concentration and relative humidity on the removal of α-pinene in a Degussa P25 supported honeycomb monolith reactor. We used the fiber optic illumination to enhance the intensity of UV-light irradiating on the Degussa P25 photocatalyst. The α-pinene conversion increased with the increase of gas flow rate indicating that the reaction rate was associated with the gaseous phase mass transfer. The α-pinene conversion varied between 91% and 96% in the range of inlet α-pinene concentration (400–2400 ppb) and relative humidity (30–70%) examined. The kinetics fits the Langmuir–Hinshelwood model. The rate coefficient (k) of α-pinene under RH30%, 50% and 70% was 0.82, 0.24, and 0.18 μmol m−2s−1, respectively. The competitive Langmuir adsorption constants for α-pinene under RH30%, 50% and 70% were 0.17, 0.56 and 1.74 ppm−1, respectively. The effect of relative humidity on α-pinene conversion depends on the inlet α-pinene concentration and raising relative humidity in sum has a positive effect on the reduction of partially oxidized intermediates within the range investigated.

Improving the collection efficiency of the liquid impinger for ultrafine particles and viral aerosols by applying granular bed filtration

Abstract Liquid impingers are utilized to collect bioaerosols for many advantages, such as avoiding dehydration of biological agents. However, many previous studies have reported that the liquid impingers are surprisingly inefficient for the collection of ultrafine bioaerosols, with collection efficiencies <30%. In the present work, we have successfully improved the collection efficiency of the liquid impinger (AGI30) to as high as 99% for particles in the size range of 20–400nm with the aid of packed glass beads. We also systematically investigated the effects of influential factors on the collection efficiency. These factors include the volume of the sampling liquid (0, 20 and 30mL), depth (0, 7 and 10cm) of packed glass beads and sampling flow rate (4, 6 and 8 liter per min, lpm). According to our experimental results, increasing the depth of packed glass beads and the volume of sampling liquid can enhance the collection efficiency. Also, decreasing the sampling flow rate can increase the collection efficiency and reduce the loss of sampling liquid. For the sampling of viable MS2 phages, the collection efficiency of AGI30 sampler with packed glass beads is much higher than that without packed glass beads. Conclusively, this study validates that the granular bed filtration can enhance the collection efficiency of liquid impingers for submicron and ultrafine particles and viral aerosols.