TiO2 mediated photocatalytic inactivation of airborne bacteria

TiO2 MEDIATED PHOTOCATALYTIC INACTIVATION OF AIRBORNE BACTERIA AMRITA PAL NATIONAL UNIVERSITY OF SINGAPORE 2007 TiO2 MEDIATED PHOTOCATALYTIC INACTIVATION OF AIRBORNE BACTERIA AMRITA PAL B. ENGG. (HONS.), JADAVPUR UNIVERSITY, INDIA A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMICAL AND BIOMOLECULAR ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2007 Name: Amrita Pal. Degree: PhD. Dept.: Chemical and Biomolecular Engineering. Thesis Title: TiO2 Mediated Photocatalytic Inactivation of Airborne Bacteria. Abstract Microbial pollutants such as bacteria are one of the significant sources of indoor air pollution. The first phase of this research aims to examine inactivation efficiencies of eight bacterial species using a batch disinfection system with TiO2 assisted photocatalytic reactions coupled with a fluorescent light or UV-A lamp. The maximum inactivation of most bacteria was achieved at an optimum TiO2 loading of 511-1666 mg/m2 corresponding to a thickness of 294 - 438 nm of TiO2 layer on the surface. Gram-negative bacterium E. coli K-12 was most effectively inactivated with a rate constant of 0.2442 min-1, while Gram-positive Bacillus subtilis exhibited the most resistant response to the photocatalytic treatment (0.0057 min-1). In the second phase, a continuous reaction system was developed to examine effects of light intensity (0.5 to 3.4 mW/cm2), TiO2 loadings (960 and 1516 mg/m2) and relative humidity (RH) (51 ± 0.61 to 85 ± 4.7%) on inactivation efficiencies of aerosolized Gram-negative bacterium E. coli K-12. Results showed an increase in bacterial inactivation with increasing UV-A intensity, TiO2 loading and RH. E. coli K-12 is fully and continuously inactivated after 15 of UV-A exposure. Keywords: TiO2; UV-A; E. coli K-12; Relative humidity; Inactivation efficiency; Continuous reaction system; ACKNOWLEDGEMENTS To begin with, I would like to express my sincere gratitude to my Supervisor Dr. Liya E. Yu for her untiring and continuous guidance throughout my entire candidature. Her advice along with constructive and critical evaluations helped me in invoking further thinking in my research area and successful completion of my studies. I would like to express my heartfelt gratitude to Dr. Madhumita B. Ray for introducing me to my current research area of Photocatalytic inactivation of Bioaerosols and guiding and supporting me throughout my research. I would also take this opportunity to thank Dr. Simo O. Pehkonen for providing invaluable ideas and advice in further enriching my research. I am also grateful to other students in our research group specially, Dr. Yang Liming and Mr. Gao Yonggang, Mr. Lim Jaehyun, Mr. Zhou Hu and Mr. Balasubramanian Suresh Kumar, for their utmost help through valuable discussions. I wish to sincerely thank our lab officers Mdm. Susan, Mdm. Li Xiang, Mdm. Sylvia, Mr. Boey, and Mdm. Mary. I would also like to express my sincere gratitude to Mr. Ng for constructing the continuous reactor. I wish to express my deep gratitude to my family members and my husband for their whole-hearted and unconditional support throughout my research. Finally, I would like to acknowledge the financial support received from the National University of Singapore, in the form of Research Scholarship. i Table of Contents Page ACKNOWLEDGEMENTS i TABLE OF CONTENTS ii SUMMARY vi LIST OF TABLES ix LIST OF FIGURES x NOMENCLATURE xii CHAPTER INTRODUCTION 1.1 Background 1.2 Objectives 1.3 Organization of thesis CHAPTER LITERATURE REVIEW 2.1 Indoor air pollution due to microbial pollutants 2.2 Effect of direct UV irradiation on bacteria 2.3 Effect of heterogeneous photocatalysis (UV-A and TiO2) on bacteria 11 2.3.1 Heterogeneous photocatalytic inactivation of bacteria in aqueous phase 13 2.3.2 Heterogeneous photocatalytic inactivation of bacteria in air phase 15 2.4 Effect of heterogeneous photocatalysis (fluorescent light and TiO2) on bacteria 16 2.5 Factors affecting the inactivation of bacteria 17 ii 2.6 2.5.1 Wavelength and light intensity 17 2.5.2 Type of bacteria 18 2.5.3 Concentration of TiO2 19 2.5.4 Crystal structure and loading of TiO2 20 2.5.5 Reaction time 21 2.5.6 Relative humidity 22 2.5.7 Temperature 24 2.5.8 Presence of interfering species 25 Current trends in Heating Ventilation and Air Conditioning (HVAC) systems CHAPTER EXPERIMENTAL 3.1 Materials 25 29 29 3.1.1 Titanium dioxide 29 3.1.2 Bacteria strains 29 3.1.3 Irradiation source 32 3.2 Experimental setup 32 3.2.1 Batch inactivation system 32 3.2.2 Continuous inactivation system 33 3.3 Experimental procedure 35 3.3.1 Bacterial culture preparation 35 3.3.2 Coating of membrane filter 36 3.3.2.1 Batch studies 36 3.3.2.2 Continuous studies 39 iii 3.3.3 Inactivation procedure 40 3.3.3.1 Batch studies 40 3.3.3.2 Continuous studies 41 3.3.4 Control experiments for batch photocatalytic studies CHAPTER RESULTS AND DISCUSSION 44 4.1 Batch photocatalysis 4.1.1 Bacteria inactivation without TiO2 43 44 under fluorescent irradiation 44 4.1.2 Bacteria inactivation under fluorescent irradiation and TiO2 (Degussa P25) 46 4.1.3 Inactivation of all bacteria 48 4.1.4 Comparison of fluorescent light inactivation with UV-A inactivation 52 4.1.5 Comparison of photocatalytic inactivation between two TiO2 catalysts, Degussa P25 and Hombikat UV-100 55 4.2 Continuous photocatalytic studies 59 4.2.1 Establishment of adsorption equilibrium 59 4.2.2 Effect of UV-A intensity on the inactivation of E. coli K12 60 4.2.3 Effect of TiO2 loadings on the inactivation of E. coli K12 62 4.2.4 Effect of relative humidity on the inactivation of E. coli K-12 64 4.2.5 Comparison between batch and continuous reaction studies 69 4.2.6 Establishment of rate equation using nonlinear regression analysis 69 iv 4.2.7 Photocatalytic reactor- scale up from bench-scale to a commercial unit CHAPTER CONCLUSIONS AND FUTURE WORK 5.1 Conclusions 75 79 79 5.1.1 Batch photocatalytic inactivation studies 80 5.1.2 Continuous photocatalytic inactivation studies 81 5.2 Future work 82 Photocatalytic inactivation effect on other strains of bacteria 82 Mechanisms of TiO2 photocatalysis disinfection 83 REFERENCES 84 APPENDICES Appendix A 98 Appendix B 110 Appendix C 111 Appendix D 112 LIST OF PUBLICATIONS 118 v SUMMARY Under a suitable environment, airborne bacteria can proliferate on various indoor materials, such as in heating ventilation and air conditioning (HVAC) systems, leading to undesired symptoms and responses associating with indoor air bioaerosols, such as sick building syndromes, bronchitis, airborne transmission of tuberculosis, asthma, etc. This can be particularly serious in tropical regions like Singapore due to high relative humidity and warm temperatures throughout the year. While inactivation of bioaerosols using TiO2 photocatalytic reactions had not been studied in detail, TiO2 photocatalytic disinfection can be promising because irradiation of UV-A activates TiO2 reactions with water and oxygen forming OH radicals (·OH) and reactive oxygen species (ROS), which can subsequently induce inactivation of bacteria. Hence, the objective of this work was to systematically examine disinfection efficiencies of TiO2 photocatalytic disinfection systems by investigating effects of catalyst loadings, bacteria species, light intensity, relative humidity, and/or system design. The first phase of this study investigated the efficacy of TiO2 mediated inactivation of eight bacterial species in a batch system using two radiation sources, a fluorescent (3900 Lux) light emitting a small amount of UV-A (0.013 mW/cm2 at 365 nm) and a UV-A lamp (4.28 mW/cm2 at wavelength 365 nm) in a batch disinfection system. Loadings of TiO2, varying from 234-8662 mg/m2, were impregnated on membrane filters and exposed to radiation source for the inactivation of eight bacteria (E. coli K-12, Pseudomonas fluorescens, Bacillus subtilis, Microbacterium sp., Microbacteriaceae str. W7, Kocuria sp. KMM 3905, Paenibacillus sp. SAFN-007 and vi Gordonia terrae/ Actinomycetaceae). Overall, the inactivation rate increased with an increase in the TiO2 loading, while the maximum inactivation of most bacteria was achieved at an optimum TiO2 loading of 511-1666 mg/m2, corresponding to a thickness of 294-438 nm of TiO2 coating over the filter surfaces. Gram-negative bacterium E. coli K-12 was most effectively inactivated (0.2442 min-1), while Gram-positive Bacillus subtilis was most resistant to the batch photocatalytic treatment (0.0057 min-1). E. coli K12 was fully inactivated after 30 minutes of treatment at a TiO2 loading of 1666 mg/m2. Inactivation of log10 was obtained for Microbacterium sp., Paenibacillus sp. SAFN-007 and Microbacteriaceae str. W7 after hours of illumination with a TiO2 loading of 1116 mg/m2. The inactivation rates resulting from the irradiation of a UV-A lamp is comparable with data available in literature, indicating consistency in the UV-A photocatalytic inactivation of the microorganisms. During the second phase of this research, a continuous annular reactor was designed to characterize the TiO2 mediated inactivation of aerosolized Gram-negative bacterium E. coli K-12 (ATCC 10798) under various UV-A intensities (0.5 to 3.4 mW/cm2), relative humidities (RH) (51 ± 0.61 to 85 ± 4.7%), and two photocatalyst loadings (960 and 1516 mg/m2) at an air flow rate of l/min. Overall, inactivation of E. coli K-12 increased with an increase in TiO2 loading, UV-intensity, or RH. An UV-A dose between 0.03 to 0.204 J/cm2/l under an average UV-A intensity of 0.5 to 3.4 mW/cm2, at a residence time of 1.1 min, is strong enough to fully and continuously inactivate all incoming bacteria. Compared to the batch disinfection system, additional experiments employing a low UV-A intensity of 0.015 mW/cm2 and a TiO2 loading of vii Table A.2 T-test analyses of inactivation at various time intervals with control (TiO2 loading = mg/m2), for (a) Microbacterium sp., (b) Paenibacillus sp. SAFN-007, (c) Bacillus subtilis (d) Pseudomonas fluorescens, (e) Kocuria sp. KMM 3905, (f) Gordonia terrae/ Actinomycetaceae and (g) E. coli K-12 (a) TiO2 loading Time (min) 234 (mg/m2) 511 (mg/m2) 840 (mg/m2) 1116 (mg/m2) 1666 (mg/m2) p-value p-value p-value p-value p-value - - - - - 15 0.2600 0.0200 0.8600 0.7800 0.7600 30 0.3200 0.0120 0.4800 0.0192 0.7920 45 0.0534 0.0710 0.6600 0.0152 0.0980 60 0.0400 0.0140 0.0580 0.0180 0.0070 120 0.0140 0.0200 0.0180 0.0150 0.0160 Control data Time (min) 1.00 0.00 15 0.83 1.09 0.86 0.93 0.14 30 0.77 0.96 0.79 0.84 0.10 45 0.72 1.09 1.16 0.99 0.24 60 0.75 1.06 0.79 0.87 0.17 120 0.69 1.02 1.02 0.91 0.19 Mean Stdev 103 (b) TiO2 loading Time (min) 511 (mg/m2) 1116 (mg/m2) 1666 (mg/m2) 3490 (mg/m2) p-value p-value p-value p-value - - - - 15 0.5000 0.0000 0.0600 0.0600 30 0.0200 0.0140 0.0000 0.0000 45 0.0200 0.0000 0.0000 0.0000 60 0.0400 0.0000 0.0000 0.0200 120 0.0000 0.0000 0.0200 0.0200 Control data Time (min) 1.00 0.00 0.92 0.91 0.91 0.91 0.01 0.73 0.83 0.80 0.79 0.05 0.68 0.77 0.62 0.69 0.08 0.58 0.61 0.61 0.60 0.02 0.46 0.55 0.38 0.46 0.09 15 30 45 60 120 Mean Stdev 104 (c) TiO2 loading Time (min) 234 (mg/m2) 511 (mg/m2) 1116 (mg/m2) 2297 (mg/m2) 3490 (mg/m2) 5778 (mg/m2) p-value p-value p-value p-value p-value p-value - - - - - - 15 0.59 0.15 0.42 0.03 0.30 0.78 30 0.29 0.17 0.02 0.10 0.03 0.57 45 0.43 0.03 0.01 0.12 0.01 0.07 60 0.31 0.48 0.11 0.05 0.00 0.00 120 0.48 0.30 0.09 0.06 0.00 0.00 Time (min) 15 30 45 60 120 Control data Mean Stdev 1.00 1.00 1.00 1.00 0.00 0.97 0.91 0.98 0.95 0.04 0.94 0.99 0.87 0.93 0.06 0.93 0.90 0.89 0.91 0.02 0.80 0.87 0.85 0.84 0.04 0.78 0.81 0.78 0.79 0.02 105 (d) TiO2 loading Time (min) Time (min) 15 30 45 60 120 840 234 (mg/m ) (mg/m ) 1666 (mg/m2) p-value p-value p-value - - - 15 0.1000 0.0700 0.1440 30 0.0480 0.0400 0.0520 45 0.0116 0.0110 0.0110 60 0.0098 0.0098 0.0098 120 0.0000 0.0000 0.0000 Control data Mean Stdev 1.00 1.00 1.00 1.00 0.00 0.50 1.05 1.38 0.98 0.44 0.65 1.06 0.55 0.75 0.27 0.63 0.62 0.85 0.70 0.13 0.52 0.52 0.70 0.58 0.10 0.39 0.43 0.43 0.42 0.02 106 (e) TiO2 loading Time (min) 234 (mg/m2) 511 (mg/m2) 1116 (mg/m2) p-value p-value p-value - - - 15 0.9200 0.7600 0.6000 30 0.9800 0.8400 0.1000 45 0.9200 1.0000 0.0800 60 0.7200 0.9800 0.4000 120 0.8400 0.3000 0.0400 Control data Time (min) 1.00 0.00 15 0.71 0.90 0.80 0.80 0.10 30 0.85 0.71 0.73 0.76 0.08 45 0.72 0.63 0.74 0.70 0.06 60 0.85 0.55 0.47 0.62 0.20 120 0.54 0.41 0.58 0.51 0.09 Mean Stdev 107 (f) TiO2 loading Time (min) 234 (mg/m2) 511 (mg/m2) 1116 (mg/m2) 1666 (mg/m2) p-value p-value p-value p-value - - - - 15 0.7600 0.4000 0.2000 0.4200 30 0.8600 0.2800 0.1600 0.1200 45 0.8000 0.0200 0.0200 0.0400 60 0.0200 0.0000 0.0200 0.0200 120 0.0000 0.0000 0.0000 0.0000 Time (min) 15 30 45 60 120 Control data Mean Stdev 1.00 0.00 0.69 1.19 1.25 1.04 0.31 0.62 0.75 1.05 0.81 0.22 0.81 1.19 1.00 1.00 0.19 1.31 1.00 1.70 1.34 0.35 0.85 1.19 1.05 1.03 0.17 108 (g) TiO2 loading Time (min) 234 (mg/m2) 511 (mg/m2) 840 (mg/m2) 1116 (mg/m2) 1666 (mg/m2) p-value p-value p-value p-value p-value - - - - - 15 0.0600 0.0000 0.0000 0.0000 0.0000 30 0.0160 0.0200 0.0200 0.0200 0.0200 45 0.0600 0.0400 0.0400 0.0400 0.0400 60 0.0000 0.0000 0.0000 0.0000 0.0000 120 0.0000 0.0000 0.0000 0.0000 0.0000 Time (min) Control data Mean Stdev 1.00 1.00 1.00 1.00 0.00 15 0.77 0.73 0.67 0.72 0.05 30 0.62 0.56 0.37 0.52 0.13 45 0.63 0.61 0.31 0.52 0.18 60 0.47 0.47 0.45 0.46 0.01 120 0.55 0.42 0.47 0.48 0.07 109 APPENDIX B Table B. Comparison of inactivation rate constant k, for Paenibacillus sp. SAFN-007 between fluorescent lamp and UV-A lamp. Fluorescent lamp was at an UV-A intensity of 0.013 mW/cm2 while UV-A lamp was at an intensity of 1.5 mW/cm2, both at 365 nm TiO2 loading (mg/m2) k (min-1), using fluorescent light k (min-1) using UV-A lamp (UV-A intensity of (UV-A intensity of 0.013 mW/cm ) 1.5 mW/cm2) 0.007 0.0632 511 0.0189 0.8212 0.5795 1116 0.0246 0.8693 1666 0.0314 0.8285 110 APPENDIX C Table C. Air changes per hour (ACH) and time required for removal efficiencies of 90%, 99% and 99.99% of airborne contaminants* ACH Minutes required for a removal efficiency of: 90% 99% 99.99% 138 276 414 69 138 207 46 92 138 35 69 104 28 55 83 23 46 69 *This table has been adapted from the formula for the rate of purging airborne contaminants. Values have been derived from the formula t1 = [ln (C2 /C1) / (Q/V)] x 60, with t1 = and C2 /C1 = (removal efficiency /100), and where: t1 = initial time-point Q = air flow rate (cubic feet per hour) C1 = initial concentration of contaminant V = room volume (cubic feet) C2 = final concentration of contaminants Q /V = ACH The times given assume perfect mixing of the air within the space (i.e., mixing factor = 1). However, perfect mixing usually does not occur, and the mixing factor could be as high as 10 if air distribution is very poor. The required time is derived by multiplying the appropriate time from the table by the mixing factor that has been determined for the booth or room. The factor and required time should be included in the operating instructions provided by the manufacturer of the booth or enclosure, and these instructions should be followed. (Excerpt from: Centers for Disease Control and Prevention’s Guideline for preventing the transmission of Mycobacterium tuberculosis in health-care facilities, 1994, p. 72) 111 APPENDIX D 4.2.6 Establishment of rate equation using nonlinear regression analysis An empirical kinetic model for the photocatalytic inactivation of E. coli K-12 appropriate to describe the experimental data is developed based on nonlinear regression analysis (Behnajady and Modirshahla, 2006), incorporating parameters of UV-A intensity, TiO2 loading, and RH with a residence time of 1.1 in the photo-reactor. This empirical model was developed in this study to show how the inactivation efficiencies in the continuous reactor depends on individual tested parameters (UV-A intensity, TiO2 loading and relative humidity). The generic kinetic model can be represented as shown in Equation (4.6) below, k3 = f(I, [TiO2], [RH]) (4.6), where k3, I, [TiO2] and [RH] represent inactivation rate constant for the continuous reaction system, UV-A intensity, TiO2 loading, and relative humidity, respectively. The apparent initial inactivation rate constants kap corresponding to each parameter have been calculated from Figures 4.5 - 4.7. Figure 4.9 shows the effect of UV-A intensity on kap at a constant TiO2 loading of 1516 mg/m2 and RH of 85%. The nonlinear trend between k3 and UV-A intensity can be described using the following empirical relationship, which were established taking into account of observations of actual experimental data: 112 k3 0.0168e0.493[I] (4.7) Figure 4.10 shows the effect of TiO2 loading on kap at constant UV-A intensity of 3.4 mW/cm2 and RH of 85%. The nonlinear correlation between k3 and TiO2 loading can be described as follows: k3 0.0108e0.0015 [TiO2] (4.8) Similarly, Figure 4.11 shows the effect of RH on kap at constant UV-A intensity of 3.4 mW/cm2 and TiO2 loading of 1516 mg/m2 and the corresponding trend between k3 and RH can be demonstrated as: k3 0.1823 [RH] – 0.0598 (4.9) 113 0.10 kap = 0.0168e -1 kap (min ) 0.08 0.493[I] R = 0.844 0.06 0.04 0.02 0.00 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Intensity, I (mW/cm2) Figure 4.9: Effects of UV-A light intensity on the initial inactivation rate constant of E. coli K-12 at a constant TiO2 loading of 1516 mg/m2 and RH of 85% 114 0.12 kap = 0.0108e0.0015[TiO2] 0.10 R2 = 0.854 -1 kap (min ) 0.08 0.06 0.04 0.02 0.00 200 400 600 800 1000 1200 1400 1600 TiO2 loading, [TiO2] (mg/m2) Figure 4.10: Effect of TiO2 loading on the initial inactivation rate constant of E. coli K12 at an UV-A intensity of 3.4 mW/cm2 and RH of 85%. 115 0.10 0.09 kap = 0.1823 [RH] - 0.0598 0.08 R2 = 0.9470 kap (min-1) 0.07 0.06 0.05 0.04 0.03 0.02 0.4 0.5 0.6 0.7 0.8 0.9 Relative humidity, [RH] (%) Figure 4.11: Effect of RH on the initial inactivation rate constant of E. coli K-12 at a constant TiO2 loading of 1516 mg/m2 and UV-A intensity of 3.4 mW/cm2. Taking the obtained coefficients from equations 4.7-4.9, the empirical function can be described as: k3 = k0 × (0.0168e0.493[I]) × (0.0108e0.0015 [TiO2]) × (0.1823 [RH] – 0.0598) (4.10) Based on experimental values of UV-A intensity, TiO2 loading and RH, k0 is obtained as 84.72. Using the value of k0 in Equation 4.10 gives the final form of the kinetic model as Equation 4.11 shows. 116 k3 = 84.72 × (0.0168e0.493[I]) × (0.0108e0.0015 [TiO2]) × (0.1823 [RH] – 0.0598) (4.11) Figure 4.12 shows how reaction rate constants estimated using the formulated empirical equation (4.11) fit with experimentally obtained values (R2 = 0.9704). It should be noted that while this empirical model can predict the inactivation rate constants of E. coli K-12 at a constant residence time of 1.1 using the reaction system in this study, changes in flow rate (or residence time) and bacteria species would require customized revision of coefficients in the model, along with additional verification. 0.07 0.05 -1 Calculated k3 (min ) 0.06 0.04 0.03 0.02 0.01 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 Experimental k3 (min-1) Figure 4.12: Comparison between experimental and calculated rate constants for inactivation of E. coli K-12 in presence of UV-A and TiO2 and different operational parameters. 117 LIST OF PUBLICATIONS • Pal, A., S.O. Pehkonen, L.E. Yu and M.B. Ray. Photocatalytic Inactivation of Grampositive and Gram-negative Bacteria using Fluorescent Light. Journal of Photochemistry and Photobiology, A: Chemistry 186, pp.335-341. 2007. • Pal, A., X. Min, L.E. Yu, S.O. Pehkonen and M.B. Ray. Photocatalytic Inactivation of Bioaerosols by TiO2 Coated Membrane. International Journal of Chemical Reactor Engineering 3, pp.1-14, 2005. 118 [...]... Effect of UV-A light intensity on the initial inactivation rate constant of E coli K-12 at a constant TiO2 loading of 1516 mg/m2 and RH of 85% 71 Figure 4.10 Effect of TiO2 loading on the initial inactivation rate constant of E coli K-12 at an UV-A intensity of 3.4 mW/cm2 and RH of 85% 72 Figure 4.11 Effect of RH on the initial inactivation rate constant of E coli K-12 at a constant TiO2 loading of 1516... a function of lapse time (min) under the condition of TiO2 loading of 1516 mg/m2, relative humidity of 97 ± 2.5%, air flow-rate of 1 lpm, and in darkness 60 Survival ratio (Nt/N0) of E coli K-12 as a function of lapse time (min) under a TiO2 loading of 1516 mg/m2, relative humidity of 85 ± 4.7%, and four UV-A intensities 62 Figure 4.5 x Figure 4.6 Effect of TiO2 loading on inactivation of E coli K-12... K-12 under UV-A intensity of 3.4 mW/cm2, relative humidity of 85 ± 4.7%, and flow rate of 1 lpm 64 Figure 4.7 Effect of RH on inactivation of E coli K-12 at a UV-A intensity of 3.4 mW/cm2 (a) without TiO2, and (b) at TiO2 of 1516 mg/m2 66 Figure 4.8 Langmuir-Hinshelwood model applied to kinetic studies on effect of relative humidity Here ‘r’ is the initial rate of inactivation of E coli K-12, obtained... Figure 4.2 Photocatalytic inactivation of E coli K-12 at various TiO2 loadings Each point is an average of triplicate experiments 46 Figure 4.3 (a) Inactivation rate constant vs the TiO2 loading for Gramnegative and Gram-positive bacteria, (b) Inactivation rate constant vs the TiO2 loading for Gram-positive bacteria, enlarged from (a) 49 Figure 4.4 Triplicate measurements of adsorption and loss of E coli...1516 mg/m2 in the continuous flow reactor showed comparable inactivation rate of bacteria viii List of Tables Table 3.1 TiO2 loading and the resultant thickness of the TiO2 coating on the membrane The error is based on a replicate of five data sets 38 Table 3.2 Numbers of dips and TiO2 coatings on filters 40 Table 4.1 Inactivation rate constants of E coli K-12, Microbacterium sp and Bacillus subtilis using... sp., Microbacteriaceae str W7, Kocuria sp KMM 3905, Paenibacillus sp SAFN-007, and Gordonia terrae/ Actinomycetaceae) using TiO2 photocatalysis 2 To examine the effects of the wavelength of radiation and intensity, TiO2 loadings, relative humidity and temperature on the batch photocatalytic inactivation system The second phase of this study is to explore the applications of TiO2 mediated photocatalytic. .. utilization of existing resources (i.e., TiO2 coupled with fluorescent light), or TiO2 coupled with UV light to inactivate bioaerosols, systematic examination of both approaches considering various parameters (e.g., relative humidity) in a typical room environment is needed Hence, the objective of the first phase of this study is to study, in batch, the photocatalytic inactivation on various strains of bacteria. .. objective of this study is to establish the inactivation kinetics of eight bacterial strains using commercial fluorescent light with TiO2 5 photocatalyst, and compare the results with the inactivation studies using UV-A radiation The specific objectives are: 1 To study the batch inactivation of selected two Gram-negative bacteria (E coli K-12 and Pseudomonas fluorescens) and six Gram-positive bacteria. .. photocatalysis 54 Table 4.2 Percentage of inactivation of E coli K-12 at various TiO2 loadings after 15 minutes of exposure to fluorescent and UVA lamp, both at an UV-A intensity of 0.013 mW/cm2 and 365 nm 55 Table 4.3 Inactivation rate constant k, of Paenibacillus sp SAFN-007 using Hombikat UV-100 and Degussa P25 with fluorescent light emitting a small fraction of UV-A intensity of 0.013 mW/cm2 at 365 nm The... continuous reaction system for the photocatalytic inactivation of aerosolized Gram-negative bacterium E coli K-12 4 To characterize effects of UV-A intensity, relative humidity, and TiO2 loading on photocatalytic inactivation of E coli K-12 in this continuous reaction system 6 1.3 Organization of thesis Following Chapter 1, which introduces the background information and motivation of conducting this study, . TiO 2 MEDIATED PHOTOCATALYTIC INACTIVATION OF AIRBORNE BACTERIA AMRITA PAL NATIONAL UNIVERSITY OF SINGAPORE 2007 TiO 2 MEDIATED PHOTOCATALYTIC INACTIVATION. (UV-A and TiO 2 ) on bacteria 11 2.3.1 Heterogeneous photocatalytic inactivation of bacteria in aqueous phase 13 2.3.2 Heterogeneous photocatalytic inactivation of bacteria in air phase. of UV-A intensity on the inactivation of E. coli K- 12 60 4.2.3 Effect of TiO 2 loadings on the inactivation of E. coli K- 12 62 4.2.4 Effect of relative humidity on the inactivation of