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Study on the Concentration and Distribution of the Airborne Bacteria in Indoor Air in the Lecture Theatres at Tianjin Chengjian University, China
Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 121 (2015) 33 – 36
9th International Symposium on Heating, Ventilation and Air Conditioning (ISHVAC) and the 3rd International Conference on Building Energy and Environment (COBEE)
Study on the Concentration and Distribution of the Airborne Bacteria in Indoor Air in the Lecture Theatres at Tianjin Chengjian University, China Dexing Guana, Chunmei Guoa, Yanju Lia,*, Haoqi Lva, and Xiaojuan Yua a
School of Energy and Safety Engineering, Tianjin Chengjian University, Tianjin, China
Abstract The research on distribution characteristics of bioaerosols in the indoor environment had the vital significance in improving indoor air quality, preventing and controlling the spread of the disease related indoor air, especially for lecture theatres which had the characteristic of step height, the more population density, stronger fluidity and the higher risk of infecting some disease. The bioaerosols distribution characteristics of indoor air in the amphitheatre were studied under the condition of the different time and methods. Using natural sedimentation method and air planktonic bacteria sampling method, the airborne bacteria were sampled in typical amphitheatre. The result showed that airborne bacteria concentration by natural sedimentation method was between 209 to 838CFU m-3, while the concentration used air planktonic bacteria sampling method was in the range of 353 to 1932CFU m-3. The mechanism of the two methods led to the difference of sampling results. Using natural sedimentation method, the concentration at 21 o'clock was among 210 ~ 419 CFU m-3, and the concentration in the next day 9:00 o'clock was at the 52 to 157 CFU m-3 range ˈthis implied that most of the larger particle size microbial particles had fallen to the ground after 12 hours. © 2015 2015The TheAuthors. Authors. Published by Elsevier Ltd. © Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of ISHVACCOBEE 2015. Peer-review under responsibility of the organizing committee of ISHVAC-COBEE 2015
Keywords: Bioaerosols; Distribution characteristics; Lecture theatres; Airborne bacteria concentration;
1. Introduction Bioaerosols concentration has become the important factor in affecting indoor air quality. When the concentration increase significantly[1]. Lots of reported results had showed that the biological aerosols, such as bacteria and virus,
* Corresponding author. Tel.: +86-136-621-51716. E-mail address:[email protected],[email protected]
1877-7058 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of ISHVAC-COBEE 2015
doi:10.1016/j.proeng.2015.08.1015
34
Dexing Guan et al. / Procedia Engineering 121 (2015) 33 – 36
of biological aerosols in indoor environment increased, the risk of infecting bacteria or allergic reactions would were airborne transmitting in the air. When an infectious person sneezed, coughed or spoke, the droplets with pathogenic bacteria would spread to other indoor places through the turbulent dispersion, which could increase the risk of infection to neighboring persons [2, 3, 4]. The problems of preventing and controlling the spread of the disease related indoor air have captured public attention. More researches on bioaerosols in medical facilities which had high risk of infection and the concern were carried out than those in lecture theatres with the above characteristic which also needed our attention [4, 5, 6]. The intention of this study was to explore the distribution characteristics of airborne bacteria in an amphitheater with natural ventilation in a university of Tianjin city in winter, and gave some suggestions on assessing indoor air quality in university classrooms in Tianjin. Furthermore, the experiments were also conducted on the size distribution of biological aerosols indoor air in the lecture theatres, the data of this paper and the above content was reported on a new paper in the future. 2. Methods The bioaerosols distribution characteristics of indoor air in the amphitheatre were studied under the condition of the different time and methods. Using natural sedimentation method (NSM) and air planktonic bacteria sampling method, the airborne bacteria were sampled in typical amphitheatre. For natural sedimentation method, the colonyforming units (CFU) per cubic meter of indoor air were calculated by the Omeilianski formula after the number of colonies was counted. For air planktonic bacteria sampling method, planktonic bacteria sampling formula was used. For natural sedimentation method, nine sampling points were set in the amphitheatre, and three plates of NutrientBroth-Medium were put at each sampling point in order to improve the accuracy of sampling data. And they were placed in the center of the studied rooms at a height of about 1.0m above the floor. The sampling time was 15 minutes in our experiments. The type of sampler was ETW-6, which was produced by Liaoyang of china. This impactor could measure the number of air microorganism and aerodynamic cut-size diameters. The impactor with aerodynamic cutsize diameters of 7.0, 4.7, 3.3, 2.1, 1.1 and 0.65μm was placed at a height of about 1.2m in the amphitheatre. The interval of sampling time was 3 minutes. During sampling, the temperature and relative humidity of indoor air were tested and recorded. The microorganisms were collected in the Nutrient-Broth-Medium in Petri-dishes which were placed on all impactor stages. All plates of Nutrient-Broth-Medium were incubated at 37ć for 48 hours. And after that the number of colonies was counted out. The data processing of this experiment used Pared-Samples T Test by SPSS 19. 3. Results and discussions Table 1 showed that the mean bioaerosols concentration in the studied amphitheatre was 476 CFUm-3 by natural sedimentation method, while the mean bioaerosols concentration was 1011CFUm-3 by the air planktonic bacteria sampling method. The results with air planktonic bacteria sampling method agreed well with the data obtained by other experts[7], who obtained that the bacteria and fungi levels of different indoor environments varied with a large extent (10 –103 CFU/m3). The different sampling methods were the major reason resulted in the difference of concentration in the same place. According to the mechanism of the sampling methods, the microbial particles were fallen into the plate of Nutrient-Broth-Medium under the effect of gravity though natural sedimentation method, which only contained larger particles in the air. Chen reported that microbial particles were collected in the size of >7.7m using natural sedimentation method [8]. But through air planktonic bacteria sampling method, the microbial particles suspended in the air were collected respectively on the sampling medium surface according to the size levels by a sampler, which contained the microbial particles in the size range of more than 0.65m (the range of the Andersen Sampler). So the number of microbial particles measured by our group fallen into the plates under the effect of gravity was less than the number of microbial particles under the suction of pump.
35
Dexing Guan et al. / Procedia Engineering 121 (2015) 33 – 36 Table 1. The bioaerosols concentration in the studied room for different methods Bioaerosols concentration[CFUm-3]
Temperature
R. H.
22ć±1.5ć
34%±2%
Method Cc + s
Min
Max
Median
NSM
476+198.3
209
838
419
Andersen sampler
1011+582.1
353
1932
795
Bioaerosol concentration[CFUm-3]
The sample size: N=30 for natural sedimentation method, N=36 for air planktonic bacteria sampling method, Cc represents the mean of bioaerosols concentration, s is the standard deviations.
500 400 300 200
the evening at nine o'clock
100
the next morning at nine o'clock
0 1
2
3
4
5
The experiment number
Fig.1. The concentration of the studied room at different sampling time with natural sedimentation method for five experiments (The bioaerosols were sampled at different sampling times with natural sedimentation method and five experiments were conducted at the same condition, the concentration was mean value of each sample, the number of samples was 18 in one experiment, the total number of samples: N=90, p<0.05)
As seen from fig.1, the concentration of bioaerosols at 21 o'clock was 314 + 82.85 (Cc + s) CFU m-3, while the concentration at 9:00 o'clock the next day was 105 + 41.43 (Cc + s) CFU m-3 through natural sedimentation method. These data was the same magnitude, but different. The dispersion of bioaerosols was influenced on its physical and biological attributes. Physical parameters, such as forces, temperature, R.H., velocity and so on, mainly affected the movement characteristics of bioaerosols. And the forces included gravity, drag force, thermophoresis force and Brown force[9]. At night, the indoor environment was relatively stable with no air disturbance and human occupancy. Some forces except the gravity could be ignored because their order of magnitude was too small to be compared with the gravity for large microbial particles. This implied that most microbial particles with larger particle size fell to the ground after 12 hours. So the concentration measured in the next morning was small than the concentration measured in the evening. 4. Conclusions The current research analyzes the cause of different results with two sampling methods, and points out that the concentration could change for different sampling time at a relatively stable indoor environment. Finally, as estimated, it is safe to be exposed to airborne bacteria in the studied room, since the concentration levels were lower than the reference standard˄2500 CFUm-3˅ evaluated by “Indoor Air Quality Standard” of China (GB/T18883-2002). Acknowledgements
36
Dexing Guan et al. / Procedia Engineering 121 (2015) 33 – 36
This work was financially supported by the Natural Science Foundation of China (51308372) and Research Fund for the Doctoral Program of Tianjin Chengjian University.
References [1] Z. D. Bolashikov and A. K. Melikov, Methods for air cleaning and protection of building occupants from airborne pathogens, Build Environ. 44 (2009) 1378-1385. [2] A.A. Aliabadi, S.N. Rogak, K.H. Bartlett, S. I. Green, Preventing airborne disease transmission: review of methods for ventilation design in health care facilities, Advances in Preventive Medicine. 21 (2011). [3] A. Mangili and M. A. Gendreau, Transmission of infectious diseases during commercial air travel, Lancet. 365 (2005) 989-996. [4] J.W. Tang, Y. Li, I. Eames, P. K. S. Chan , G. L. Ridgway, Factors involved in the aerosol transmission of infection and control of ventilation in healthcare premises, J Hosp Infect. 64 (2006) 100-114. [5] J. Qian, D. Hospodsky, N. Yamamoto, W. W. Nazaroff, J. Peccia1, Size-resolved emission rates of airborne bacteria and fungi in an occupied classroom, Indoor Air. 22 (2012) 339-351. [6] W.-H. Ching, M. K. H. Leung, D. Y. C. Leunga, Y. Li, P. L. Yuen, Reducing risk of airborne transmitted infection in hospitals by use of hospital curtains, Indoor Built Environ. 17 (2008) 252–259. [7] S. Mentes, M. Arisoy, A. Y. Rad, G. Gullu, Bacteria and fungi levels in various indoor and outdoor environments in Ankara, Turkey, Clean. 37 (2009) 487-493. [8] X.Y. Chen, Y. H. Bi, B. Li, Comparison of methodologies to determine the granularity distribution of airborne bacteria, Acta Scientiae Circumstantiae. 28 (2008) 589 -592. [9] S. C. Christopher and M.W. Christopher, Bioaerosols Handbook, 1995, pp. 160-170.
ScienceDirect Procedia Engineering 121 (2015) 33 – 36
9th International Symposium on Heating, Ventilation and Air Conditioning (ISHVAC) and the 3rd International Conference on Building Energy and Environment (COBEE)
Study on the Concentration and Distribution of the Airborne Bacteria in Indoor Air in the Lecture Theatres at Tianjin Chengjian University, China Dexing Guana, Chunmei Guoa, Yanju Lia,*, Haoqi Lva, and Xiaojuan Yua a
School of Energy and Safety Engineering, Tianjin Chengjian University, Tianjin, China
Abstract The research on distribution characteristics of bioaerosols in the indoor environment had the vital significance in improving indoor air quality, preventing and controlling the spread of the disease related indoor air, especially for lecture theatres which had the characteristic of step height, the more population density, stronger fluidity and the higher risk of infecting some disease. The bioaerosols distribution characteristics of indoor air in the amphitheatre were studied under the condition of the different time and methods. Using natural sedimentation method and air planktonic bacteria sampling method, the airborne bacteria were sampled in typical amphitheatre. The result showed that airborne bacteria concentration by natural sedimentation method was between 209 to 838CFU m-3, while the concentration used air planktonic bacteria sampling method was in the range of 353 to 1932CFU m-3. The mechanism of the two methods led to the difference of sampling results. Using natural sedimentation method, the concentration at 21 o'clock was among 210 ~ 419 CFU m-3, and the concentration in the next day 9:00 o'clock was at the 52 to 157 CFU m-3 range ˈthis implied that most of the larger particle size microbial particles had fallen to the ground after 12 hours. © 2015 2015The TheAuthors. Authors. Published by Elsevier Ltd. © Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of ISHVACCOBEE 2015. Peer-review under responsibility of the organizing committee of ISHVAC-COBEE 2015
Keywords: Bioaerosols; Distribution characteristics; Lecture theatres; Airborne bacteria concentration;
1. Introduction Bioaerosols concentration has become the important factor in affecting indoor air quality. When the concentration increase significantly[1]. Lots of reported results had showed that the biological aerosols, such as bacteria and virus,
* Corresponding author. Tel.: +86-136-621-51716. E-mail address:[email protected],[email protected]
1877-7058 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of ISHVAC-COBEE 2015
doi:10.1016/j.proeng.2015.08.1015
34
Dexing Guan et al. / Procedia Engineering 121 (2015) 33 – 36
of biological aerosols in indoor environment increased, the risk of infecting bacteria or allergic reactions would were airborne transmitting in the air. When an infectious person sneezed, coughed or spoke, the droplets with pathogenic bacteria would spread to other indoor places through the turbulent dispersion, which could increase the risk of infection to neighboring persons [2, 3, 4]. The problems of preventing and controlling the spread of the disease related indoor air have captured public attention. More researches on bioaerosols in medical facilities which had high risk of infection and the concern were carried out than those in lecture theatres with the above characteristic which also needed our attention [4, 5, 6]. The intention of this study was to explore the distribution characteristics of airborne bacteria in an amphitheater with natural ventilation in a university of Tianjin city in winter, and gave some suggestions on assessing indoor air quality in university classrooms in Tianjin. Furthermore, the experiments were also conducted on the size distribution of biological aerosols indoor air in the lecture theatres, the data of this paper and the above content was reported on a new paper in the future. 2. Methods The bioaerosols distribution characteristics of indoor air in the amphitheatre were studied under the condition of the different time and methods. Using natural sedimentation method (NSM) and air planktonic bacteria sampling method, the airborne bacteria were sampled in typical amphitheatre. For natural sedimentation method, the colonyforming units (CFU) per cubic meter of indoor air were calculated by the Omeilianski formula after the number of colonies was counted. For air planktonic bacteria sampling method, planktonic bacteria sampling formula was used. For natural sedimentation method, nine sampling points were set in the amphitheatre, and three plates of NutrientBroth-Medium were put at each sampling point in order to improve the accuracy of sampling data. And they were placed in the center of the studied rooms at a height of about 1.0m above the floor. The sampling time was 15 minutes in our experiments. The type of sampler was ETW-6, which was produced by Liaoyang of china. This impactor could measure the number of air microorganism and aerodynamic cut-size diameters. The impactor with aerodynamic cutsize diameters of 7.0, 4.7, 3.3, 2.1, 1.1 and 0.65μm was placed at a height of about 1.2m in the amphitheatre. The interval of sampling time was 3 minutes. During sampling, the temperature and relative humidity of indoor air were tested and recorded. The microorganisms were collected in the Nutrient-Broth-Medium in Petri-dishes which were placed on all impactor stages. All plates of Nutrient-Broth-Medium were incubated at 37ć for 48 hours. And after that the number of colonies was counted out. The data processing of this experiment used Pared-Samples T Test by SPSS 19. 3. Results and discussions Table 1 showed that the mean bioaerosols concentration in the studied amphitheatre was 476 CFUm-3 by natural sedimentation method, while the mean bioaerosols concentration was 1011CFUm-3 by the air planktonic bacteria sampling method. The results with air planktonic bacteria sampling method agreed well with the data obtained by other experts[7], who obtained that the bacteria and fungi levels of different indoor environments varied with a large extent (10 –103 CFU/m3). The different sampling methods were the major reason resulted in the difference of concentration in the same place. According to the mechanism of the sampling methods, the microbial particles were fallen into the plate of Nutrient-Broth-Medium under the effect of gravity though natural sedimentation method, which only contained larger particles in the air. Chen reported that microbial particles were collected in the size of >7.7m using natural sedimentation method [8]. But through air planktonic bacteria sampling method, the microbial particles suspended in the air were collected respectively on the sampling medium surface according to the size levels by a sampler, which contained the microbial particles in the size range of more than 0.65m (the range of the Andersen Sampler). So the number of microbial particles measured by our group fallen into the plates under the effect of gravity was less than the number of microbial particles under the suction of pump.
35
Dexing Guan et al. / Procedia Engineering 121 (2015) 33 – 36 Table 1. The bioaerosols concentration in the studied room for different methods Bioaerosols concentration[CFUm-3]
Temperature
R. H.
22ć±1.5ć
34%±2%
Method Cc + s
Min
Max
Median
NSM
476+198.3
209
838
419
Andersen sampler
1011+582.1
353
1932
795
Bioaerosol concentration[CFUm-3]
The sample size: N=30 for natural sedimentation method, N=36 for air planktonic bacteria sampling method, Cc represents the mean of bioaerosols concentration, s is the standard deviations.
500 400 300 200
the evening at nine o'clock
100
the next morning at nine o'clock
0 1
2
3
4
5
The experiment number
Fig.1. The concentration of the studied room at different sampling time with natural sedimentation method for five experiments (The bioaerosols were sampled at different sampling times with natural sedimentation method and five experiments were conducted at the same condition, the concentration was mean value of each sample, the number of samples was 18 in one experiment, the total number of samples: N=90, p<0.05)
As seen from fig.1, the concentration of bioaerosols at 21 o'clock was 314 + 82.85 (Cc + s) CFU m-3, while the concentration at 9:00 o'clock the next day was 105 + 41.43 (Cc + s) CFU m-3 through natural sedimentation method. These data was the same magnitude, but different. The dispersion of bioaerosols was influenced on its physical and biological attributes. Physical parameters, such as forces, temperature, R.H., velocity and so on, mainly affected the movement characteristics of bioaerosols. And the forces included gravity, drag force, thermophoresis force and Brown force[9]. At night, the indoor environment was relatively stable with no air disturbance and human occupancy. Some forces except the gravity could be ignored because their order of magnitude was too small to be compared with the gravity for large microbial particles. This implied that most microbial particles with larger particle size fell to the ground after 12 hours. So the concentration measured in the next morning was small than the concentration measured in the evening. 4. Conclusions The current research analyzes the cause of different results with two sampling methods, and points out that the concentration could change for different sampling time at a relatively stable indoor environment. Finally, as estimated, it is safe to be exposed to airborne bacteria in the studied room, since the concentration levels were lower than the reference standard˄2500 CFUm-3˅ evaluated by “Indoor Air Quality Standard” of China (GB/T18883-2002). Acknowledgements
36
Dexing Guan et al. / Procedia Engineering 121 (2015) 33 – 36
This work was financially supported by the Natural Science Foundation of China (51308372) and Research Fund for the Doctoral Program of Tianjin Chengjian University.
References [1] Z. D. Bolashikov and A. K. Melikov, Methods for air cleaning and protection of building occupants from airborne pathogens, Build Environ. 44 (2009) 1378-1385. [2] A.A. Aliabadi, S.N. Rogak, K.H. Bartlett, S. I. Green, Preventing airborne disease transmission: review of methods for ventilation design in health care facilities, Advances in Preventive Medicine. 21 (2011). [3] A. Mangili and M. A. Gendreau, Transmission of infectious diseases during commercial air travel, Lancet. 365 (2005) 989-996. [4] J.W. Tang, Y. Li, I. Eames, P. K. S. Chan , G. L. Ridgway, Factors involved in the aerosol transmission of infection and control of ventilation in healthcare premises, J Hosp Infect. 64 (2006) 100-114. [5] J. Qian, D. Hospodsky, N. Yamamoto, W. W. Nazaroff, J. Peccia1, Size-resolved emission rates of airborne bacteria and fungi in an occupied classroom, Indoor Air. 22 (2012) 339-351. [6] W.-H. Ching, M. K. H. Leung, D. Y. C. Leunga, Y. Li, P. L. Yuen, Reducing risk of airborne transmitted infection in hospitals by use of hospital curtains, Indoor Built Environ. 17 (2008) 252–259. [7] S. Mentes, M. Arisoy, A. Y. Rad, G. Gullu, Bacteria and fungi levels in various indoor and outdoor environments in Ankara, Turkey, Clean. 37 (2009) 487-493. [8] X.Y. Chen, Y. H. Bi, B. Li, Comparison of methodologies to determine the granularity distribution of airborne bacteria, Acta Scientiae Circumstantiae. 28 (2008) 589 -592. [9] S. C. Christopher and M.W. Christopher, Bioaerosols Handbook, 1995, pp. 160-170.