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A Study on the Decontaminated Efficiency of Ultraviolet Device on the Indoor Airborne Bacteria
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ScienceDirect
Available online at www.sciencedirect.com Procedia Procedia Engineering Engineering 00 00 (2017) (2017) 000–000 000–000
ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Engineering 205 (2017) 1376–1380
10th International Symposium on Heating, Ventilation and Air Conditioning, ISHVAC2017, 1922 October 2017, Jinan, China
A Study on the Decontaminated Efficiency of Ultraviolet Device on the Indoor Airborne Bacteria Yanju Liaa, Min Wangaa, Dexing Guanaa, Haoqi Lvaa, Jiuwei Zhaoaa, Xiaojuan Yuaa, a,* Xiaoguang Yangaa, Chunbin Wua,* a a
School School of of Energy Energy and and Safety Safety Engineering Engineering of of Tianjin Tianjin Chengjian Chengjian University, University, No. No. 26 26 Jinjing Jinjing Road, Road, Xiqing Xiqing District, District, Tianjin Tianjin 300072, 300072, China China
Abstract Abstract The The aims aims of of this this paper paper were were studied studied bactericidal bactericidal effect effect of of the the ultraviolet ultraviolet lamp lamp on on irradiation irradiation intensity, intensity, irradiation irradiation time time and and installation installation height. height. Three Three independent independent variables variables were were set, set, such such as as irradiation irradiation intensity, intensity, irradiation irradiation time time and and installation installation height. height. By By natural natural sedimentation sedimentation method, method, the the airborne airborne bacteria bacteria were were sampled sampled before before and and after after radiation radiation of of ultraviolet ultraviolet lamp, lamp, then then the the decay decay rates rates of of airborne airborne bacteria bacteria were were calculated. calculated. The The decontaminated decontaminated efficiency efficiency were were more more than than 40% 40% when when irradiation irradiation power power of of UV UV were were 30w 30w (42.5%) (42.5%) and and 40w 40w (60%). (60%). With With the the lengthen lengthen irradiation irradiation time, time, the the better better reduced reduced rate rate of of the the airborne airborne bacteria. bacteria. The The bactericidal bactericidal effect effect of of the the ultraviolet ultraviolet lamps lamps was was in in proportion proportion to to their their irradiation irradiation intensity intensity and and in in inverse inverse proportion proportion to to their their installation height. According to the actual circumstance of university cafeteria, the arrangement of ultraviolet lamp was installation height. According to the actual circumstance of university cafeteria, the arrangement of ultraviolet lamp was that that irradiation irradiation intensity intensity was was 40W, 40W, installation installation height height was was 2.0m, 2.0m, and and irradiation irradiation time time was was 60min. 60min. © © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. © 2017 The Authors. Published by Elsevier Ltd. Peer-review Peer-review under under responsibility responsibility of of the the scientific scientific committee committee of of the the 10th 10th International International Symposium Symposium on on Heating, Heating, Ventilation Ventilation and and Air Air Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Conditioning. Conditioning. Air Conditioning. Keywords: Keywords: Ultraviolet Ultraviolet device; device; Irradiation Irradiation intensity; intensity; Irradiation Irradiation time; time; installation installation height height
1. Introduction With suspending microbial in the air, the bio-particle concentration is closely related to the personnel density and human activities. According to the crowded conditions in public area, biological particles levels have an important influence on the air quality, and threaded people health [1]. Due to human activity concentration, more movement, higher relative humidity and more organic compositions in the college canteen, classroom, library and so on, bacteria * * Corresponding Corresponding author. author. Tel.: Tel.: +086-22-23085277; +086-22-23085277; E-mail E-mail address: address: [email protected]; [email protected]; [email protected] [email protected] 1877-7058 1877-7058 © © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. Peer-review Peer-review under under responsibility responsibility of of the the scientific scientific committee committee of of the the 10th 10th International International Symposium Symposium on on Heating, Heating, Ventilation Ventilation and and Air Air Conditioning. Conditioning.
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning. 10.1016/j.proeng.2017.10.281
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Yanju Li et al. / Procedia Engineering 205 (2017) 1376–1380 Yanju Li et al. / Procedia Engineering 00 (2017) 000–000
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and other microorganisms were comparative higher [2]. Bluyssen et al [3] have reported that the bacterial pollution were light level in air handling units, filter and cooling system by investigated the air conditioning system pollution. Ultraviolet germicidal lamp was installed in indoor or air duct for the microbiological sterilization [4]. Factors affecting the disinfected efficiency of UV lamp have been known as light intensity, irradiation time, environmental temperature and humidity, installed density, ventilation, air change rate and height of the tubes and so on [5-8]. Some researches had investigated the reduction efficiency of microbiology of ultraviolet germicidal lamp, results have gained that the Ultraviolet germicidal lamp had the high efficiency on the decontamination of microbe [4,9]. The biological reduction efficiency of different series of bacteria was conducted for the ultraviolet by some experts [10,11]. In terms of the installation height, irradiation time and installation density of ultraviolet germicidal lamp have not been regulated in university canteens, this study conducted the experiments on the bacterial reduced efficiency of ultraviolet germicidal lamp and focused on the influence of installation height, density and light intensity, in order to improve the college dining room environment and suggest on the use of ultraviolet germicidal lamp. 2. Methods 2.1. Instruments and materials Ultraviolet germicidal lamp (UV lamp), autoclave(MJ78a, STIK, the United States), drying oven (101-10b, Tianjin, China), incubator (HZQ-X100, Suzhou, China), super clean workbench (SW-CJ-10, Suzhou, China), temperature and humidity meter (TSI7425, TSI, the United States), nutrient broth (AOBOX, Beijing, China), AGAR powder (AOBOX, Beijing, China), NaOH solution (0.5 mol/L). 2.2. Scheme and experimental step The investigation [12] found that although the producer and type of the UV lamp used in canteen were different with the concentrated distribution of the irradiation power. 17 investigated canteens in total were of which 2 of 20w, 11 of 30w and 4 of 40w. The installation height ranged from 2.0 to 3.25 m. In this paper, the 20w, 30w, 40w power ultraviolet germicidal were selected and the installation height was set as 1.8m, 2.0m and 2.2m. Five sampling points were installed adopting the quincunxes sampling method (Fig. 1).The UV lamp installed in the upper middle of the lab, each of the sampling points places three paralleled samples，with the heights of 0.6m away the floor.
Fig. 1. layout of the sampling points.
Experimental steps: (1) with 2.0 m installation height of UV lamp, the bacteria concentrations were sampled before turning on the lamp. And sampling the second time, with exposure of 60 min by the UV lamp with 20w. Then repeated the above experiments by the UV lamp with 30w, 40w, respectively. The interval of each experiment is 12 hours. (2) With the installation height of 2.0 m of 30w UV lamp, sample the bacteria before opening the UV lamp. Then irradiate for 30 min and sample again after the exposure of UV lamp. And experiment again with the irradiation time changed respectively into 60min and 120min. (3) with the 30w UV lamp and 30min irradiation time, the bacteria concentration was sampled without UV irradiation. At installation height of 1.8 m, the second sample
Yanju Li et al. / Procedia Engineering 205 (2017) 1376–1380 Yanju Li et al / Procedia Engineering 00 (2017) 000–000
1378
3
after 30 min irradiation. Adjust the installation height of UV lamp to 2 m and 2.2 m respectively, repeat the above experiments. The interval of each above-mentioned experiment is 12 hours. 2.3. Sampling and incubator The natural sedimentation method [13] was adopted in this paper. the plates with medium (nutrient broth18 g, AGAR powder 18 g, distilled water 1000 ml, pH 7.4-7.6) were placed at each sampling point, open the plate cover exposed for 5 min in the air, then put it into the incubator for 48h under the environment of 37 ℃, and count the colony of bacteria. The bacteria concentration was calculated by Omeliansky function [14] as follows, C=
������
D=
�� ���
(1)
��
Where C is the number of air colonies, CFU/m3. N is the colony counts of the plate. A is the culture dish area, cm2. t is exposure time, min. The decontaminated efficiency of UV lamp was calculated using equation (2), ��
(2)
× 100%
where C0 is the bacteria concentration before UV lamp irradiation, CFU/m3. C1 is the bacteria concentration after UV lamp irradiation, CFU/m3. 3. Results 3.1. Effect of power of UV lamp on the decontaminated efficiency of bacteria As shown in Fig. 2, with the UV lamp of 20W, 30W and 40W, the bacteria concentrations without the exposure of UV lamp were 734±283, 906±395 and 927±414 CFU/m3, respectively, while that with the 60min exposure were 698±507, 522±193 and 367±102 CFU/m3. Followed by function 2, the decontaminated efficiency of UV lamp was more than 40% with the higher irradiation power of 30W. The decontaminated efficiency increased with the irradiation power (20W, 30W, 40W).
Fig. 2. effect of power of UV lamp on the decontaminated efficiency of bacteria.
3.2. Effect of irradiation time on the decontaminated efficiency of bacteria By equation 1, the airborne bacteria concentrations were calculated from 806 to 1894 CFU/m3 before exposure (Fig. 3). The study obtained that the decontaminated efficiency of airborne bacteria were 11.4%, 42.5% and 38.3%
4
Yanju Li et al. / Procedia Engineering 205 (2017) 1376–1380 Yanju Li et al. / Procedia Engineering 00 (2017) 000–000
1379
respectively at the irradiation time of 30min, 60min and 120min (Fig. 3). Seen from figure 3, the reason why the decontaminated efficiency became similar when the irradiation time at 60min to 120min is that the infection of UV on the bacteria was tightly related with UV wave and the increasing of irradiation time can lead to the stable UV wave and similar reduction of the bacteria. More future work would be done about the mentioned phenomenon.
Fig. 3. the bacteria concentration and decontaminated efficiency at the exposure of different irradiation time.
3.3. Effect of installation height on the decontaminated efficiency of bacteria Without the irradiation of UV, the background concentration were gained by function 1 as 440±132, 1258±676 and 1132±132 CFU/m3 at the installation height of 1.8m, 2.0m and 2.2 m respectively. Irradiated for 30min, the bacteria counts reduced to 282±70, 817±358 and 1037±179 CFU/m3 at three heights (Fig. 4). While the UV lamp was installed at the height of 1.8m and 2.0 m, the best reduced efficiency of the bacteria (more than 35%) has obtained in the study (Fig. 4). At the height of 2.2 m, the effect of sterilization of UV lamp is poor (less than 10%). Increasing of irradiation distance, the better sterilization effects were gained. With the installation height over a certain range, the poor influence had been gained on the bacteria by the UV wave.
Fig. 4. the bacteria concentration and decontaminated efficiency with the different installation height.
4. Conclusions Analyzing the experimental results, some conclusions were made as follows. (1) When the UV power selected as 20w, 30w and 40w, the sterilization effect were sequentially obtained from the experiments. Considering the type of ultraviolet germicidal lamp in the markets, the UV device of 40W was suggested as better one. (2) The experimental results showed that the ultraviolet germicidal lamp is turned on, sterilization effect is most obvious at the continuous
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Yanju Li et al. / Procedia Engineering 205 (2017) 1376–1380 Yanju Li et al / Procedia Engineering 00 (2017) 000–000
5
irradiated for 60 min. And when the irradiation time continue to lengthen; sterilization effect has no obvious change with increasing power consumption. (3) Seen from the experimental results, the lower the installation height, the better sterilization effect at the installation height of 1.8 m and 2.0 m. For the sterilization effect, dining room space, decoration and security factors such as teachers and students, it is suggested that ultraviolet germicidal lamp should be installed at height of about 2.0 m. Acknowledgements This work was financially supported by the National Students' innovation and entrepreneurship training program (201610792007) and Students' innovation and entrepreneurship training programs of Tianjin Chengjian university (201710792058). References [1] B Fu, H Zhao, B Yong, et al. Public air microbial contamination research progress, Chin J Public Health, 28 (6) (2012) 857–858. [2] D Yu, L Ye, M Cheng, et al. Investigation of Pollutant Airbone Microbes in Campus, J Prev Med Inf, 27(10) (2011)766–769. [3] Bluyssen PM, Cox C, Seppanen O, et al. Why，when，how do HVAC-systems pollute the indoor environment and what to do about it? the European AIRLESS project, Build Environ. 38 (2003) 209–225. [4] Harstad, J.B., Decker, H.M., Wedum, A.G.. Use of ultraviolet irradiation in a room air Conditioner for removal of bacteria, Applied Microbiology, 2 (1954) 148–151. [5] Tseng, C.C., Li, C.S.. Inactivation of virus-containing aerosols by ultraviolet germicidal irradiation, Aerosol Sci Tech. 39 (2005) 1136–1142. [6] Linnes J C, Rudnick S N, Hunt G M, et al. Eggcrate UV: a whole ceiling upper-room ultraviolet germicidal irradiation system for air disinfection in occupied rooms, Indoor air. 24(2) (2014) 116–124. [7] Memarzadeh F, Olmsted R N, Bartley J M. Applications of ultraviolet germicidal irradiation disinfection in health care facilities: effective adjunct, but not stand-alone technology, Am J Infect Control. 38(5) (2010) S13–S24. [8] J Ke W Li, Y Chen. Study on disinfection efficiency by ultraviolet. Journal of environmental pollution and control. 25(3) (2003),136–138,144. [9] Kujundzic, E., Matalkah, F., Howard, C.J., Hernandez, M., Miller, S.L. UV air cleaners and upper-room air ultraviolet germicidal irradiation for controlling airborne bacteria and fungal spores, J Occup Environ Hyg. 3 (2006) 536–546. [10] Xu, P., Kujundzic, E., Peccia, J., Schafer, et al. Impact of environmental factors on efficacy of upper-room air ultraviolet germicidal irradiation for inactivating airborne mycobacteria, Environ Sci Technol. 39 (2005) 9656–9664. [11] Sung M, Kato S. Estimating the germicidal effect of upper-room UVGI system on exhaled air of patients based on ventilation efficiency, Build Environ. 46 (11) (2011) 2326–2332. [12] Y Li, S Zhao, D Niu, et al. Investigation on the usage situation of ultraviolet disinfection devices installed at university canteen. Chinese journal of disinfection. 26(2017) 145–147. [13] X Yu . Modern air microbiology. Beijing, people's military medical press. (2002)181–188. [14] Hayleeyesus S F, Ejeso A, Derseh F A. Quantitative assessment of bio-aerosols contamination in indoor air of University dormitory rooms, International Journal of Health Sciences. 9(3) (2015) 249–256.
ScienceDirect
Available online at www.sciencedirect.com Procedia Procedia Engineering Engineering 00 00 (2017) (2017) 000–000 000–000
ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Engineering 205 (2017) 1376–1380
10th International Symposium on Heating, Ventilation and Air Conditioning, ISHVAC2017, 1922 October 2017, Jinan, China
A Study on the Decontaminated Efficiency of Ultraviolet Device on the Indoor Airborne Bacteria Yanju Liaa, Min Wangaa, Dexing Guanaa, Haoqi Lvaa, Jiuwei Zhaoaa, Xiaojuan Yuaa, a,* Xiaoguang Yangaa, Chunbin Wua,* a a
School School of of Energy Energy and and Safety Safety Engineering Engineering of of Tianjin Tianjin Chengjian Chengjian University, University, No. No. 26 26 Jinjing Jinjing Road, Road, Xiqing Xiqing District, District, Tianjin Tianjin 300072, 300072, China China
Abstract Abstract The The aims aims of of this this paper paper were were studied studied bactericidal bactericidal effect effect of of the the ultraviolet ultraviolet lamp lamp on on irradiation irradiation intensity, intensity, irradiation irradiation time time and and installation installation height. height. Three Three independent independent variables variables were were set, set, such such as as irradiation irradiation intensity, intensity, irradiation irradiation time time and and installation installation height. height. By By natural natural sedimentation sedimentation method, method, the the airborne airborne bacteria bacteria were were sampled sampled before before and and after after radiation radiation of of ultraviolet ultraviolet lamp, lamp, then then the the decay decay rates rates of of airborne airborne bacteria bacteria were were calculated. calculated. The The decontaminated decontaminated efficiency efficiency were were more more than than 40% 40% when when irradiation irradiation power power of of UV UV were were 30w 30w (42.5%) (42.5%) and and 40w 40w (60%). (60%). With With the the lengthen lengthen irradiation irradiation time, time, the the better better reduced reduced rate rate of of the the airborne airborne bacteria. bacteria. The The bactericidal bactericidal effect effect of of the the ultraviolet ultraviolet lamps lamps was was in in proportion proportion to to their their irradiation irradiation intensity intensity and and in in inverse inverse proportion proportion to to their their installation height. According to the actual circumstance of university cafeteria, the arrangement of ultraviolet lamp was installation height. According to the actual circumstance of university cafeteria, the arrangement of ultraviolet lamp was that that irradiation irradiation intensity intensity was was 40W, 40W, installation installation height height was was 2.0m, 2.0m, and and irradiation irradiation time time was was 60min. 60min. © © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. © 2017 The Authors. Published by Elsevier Ltd. Peer-review Peer-review under under responsibility responsibility of of the the scientific scientific committee committee of of the the 10th 10th International International Symposium Symposium on on Heating, Heating, Ventilation Ventilation and and Air Air Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Conditioning. Conditioning. Air Conditioning. Keywords: Keywords: Ultraviolet Ultraviolet device; device; Irradiation Irradiation intensity; intensity; Irradiation Irradiation time; time; installation installation height height
1. Introduction With suspending microbial in the air, the bio-particle concentration is closely related to the personnel density and human activities. According to the crowded conditions in public area, biological particles levels have an important influence on the air quality, and threaded people health [1]. Due to human activity concentration, more movement, higher relative humidity and more organic compositions in the college canteen, classroom, library and so on, bacteria * * Corresponding Corresponding author. author. Tel.: Tel.: +086-22-23085277; +086-22-23085277; E-mail E-mail address: address: [email protected]; [email protected]; [email protected] [email protected] 1877-7058 1877-7058 © © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. Peer-review Peer-review under under responsibility responsibility of of the the scientific scientific committee committee of of the the 10th 10th International International Symposium Symposium on on Heating, Heating, Ventilation Ventilation and and Air Air Conditioning. Conditioning.
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning. 10.1016/j.proeng.2017.10.281
2
Yanju Li et al. / Procedia Engineering 205 (2017) 1376–1380 Yanju Li et al. / Procedia Engineering 00 (2017) 000–000
1377
and other microorganisms were comparative higher [2]. Bluyssen et al [3] have reported that the bacterial pollution were light level in air handling units, filter and cooling system by investigated the air conditioning system pollution. Ultraviolet germicidal lamp was installed in indoor or air duct for the microbiological sterilization [4]. Factors affecting the disinfected efficiency of UV lamp have been known as light intensity, irradiation time, environmental temperature and humidity, installed density, ventilation, air change rate and height of the tubes and so on [5-8]. Some researches had investigated the reduction efficiency of microbiology of ultraviolet germicidal lamp, results have gained that the Ultraviolet germicidal lamp had the high efficiency on the decontamination of microbe [4,9]. The biological reduction efficiency of different series of bacteria was conducted for the ultraviolet by some experts [10,11]. In terms of the installation height, irradiation time and installation density of ultraviolet germicidal lamp have not been regulated in university canteens, this study conducted the experiments on the bacterial reduced efficiency of ultraviolet germicidal lamp and focused on the influence of installation height, density and light intensity, in order to improve the college dining room environment and suggest on the use of ultraviolet germicidal lamp. 2. Methods 2.1. Instruments and materials Ultraviolet germicidal lamp (UV lamp), autoclave(MJ78a, STIK, the United States), drying oven (101-10b, Tianjin, China), incubator (HZQ-X100, Suzhou, China), super clean workbench (SW-CJ-10, Suzhou, China), temperature and humidity meter (TSI7425, TSI, the United States), nutrient broth (AOBOX, Beijing, China), AGAR powder (AOBOX, Beijing, China), NaOH solution (0.5 mol/L). 2.2. Scheme and experimental step The investigation [12] found that although the producer and type of the UV lamp used in canteen were different with the concentrated distribution of the irradiation power. 17 investigated canteens in total were of which 2 of 20w, 11 of 30w and 4 of 40w. The installation height ranged from 2.0 to 3.25 m. In this paper, the 20w, 30w, 40w power ultraviolet germicidal were selected and the installation height was set as 1.8m, 2.0m and 2.2m. Five sampling points were installed adopting the quincunxes sampling method (Fig. 1).The UV lamp installed in the upper middle of the lab, each of the sampling points places three paralleled samples，with the heights of 0.6m away the floor.
Fig. 1. layout of the sampling points.
Experimental steps: (1) with 2.0 m installation height of UV lamp, the bacteria concentrations were sampled before turning on the lamp. And sampling the second time, with exposure of 60 min by the UV lamp with 20w. Then repeated the above experiments by the UV lamp with 30w, 40w, respectively. The interval of each experiment is 12 hours. (2) With the installation height of 2.0 m of 30w UV lamp, sample the bacteria before opening the UV lamp. Then irradiate for 30 min and sample again after the exposure of UV lamp. And experiment again with the irradiation time changed respectively into 60min and 120min. (3) with the 30w UV lamp and 30min irradiation time, the bacteria concentration was sampled without UV irradiation. At installation height of 1.8 m, the second sample
Yanju Li et al. / Procedia Engineering 205 (2017) 1376–1380 Yanju Li et al / Procedia Engineering 00 (2017) 000–000
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3
after 30 min irradiation. Adjust the installation height of UV lamp to 2 m and 2.2 m respectively, repeat the above experiments. The interval of each above-mentioned experiment is 12 hours. 2.3. Sampling and incubator The natural sedimentation method [13] was adopted in this paper. the plates with medium (nutrient broth18 g, AGAR powder 18 g, distilled water 1000 ml, pH 7.4-7.6) were placed at each sampling point, open the plate cover exposed for 5 min in the air, then put it into the incubator for 48h under the environment of 37 ℃, and count the colony of bacteria. The bacteria concentration was calculated by Omeliansky function [14] as follows, C=
������
D=
�� ���
(1)
��
Where C is the number of air colonies, CFU/m3. N is the colony counts of the plate. A is the culture dish area, cm2. t is exposure time, min. The decontaminated efficiency of UV lamp was calculated using equation (2), ��
(2)
× 100%
where C0 is the bacteria concentration before UV lamp irradiation, CFU/m3. C1 is the bacteria concentration after UV lamp irradiation, CFU/m3. 3. Results 3.1. Effect of power of UV lamp on the decontaminated efficiency of bacteria As shown in Fig. 2, with the UV lamp of 20W, 30W and 40W, the bacteria concentrations without the exposure of UV lamp were 734±283, 906±395 and 927±414 CFU/m3, respectively, while that with the 60min exposure were 698±507, 522±193 and 367±102 CFU/m3. Followed by function 2, the decontaminated efficiency of UV lamp was more than 40% with the higher irradiation power of 30W. The decontaminated efficiency increased with the irradiation power (20W, 30W, 40W).
Fig. 2. effect of power of UV lamp on the decontaminated efficiency of bacteria.
3.2. Effect of irradiation time on the decontaminated efficiency of bacteria By equation 1, the airborne bacteria concentrations were calculated from 806 to 1894 CFU/m3 before exposure (Fig. 3). The study obtained that the decontaminated efficiency of airborne bacteria were 11.4%, 42.5% and 38.3%
4
Yanju Li et al. / Procedia Engineering 205 (2017) 1376–1380 Yanju Li et al. / Procedia Engineering 00 (2017) 000–000
1379
respectively at the irradiation time of 30min, 60min and 120min (Fig. 3). Seen from figure 3, the reason why the decontaminated efficiency became similar when the irradiation time at 60min to 120min is that the infection of UV on the bacteria was tightly related with UV wave and the increasing of irradiation time can lead to the stable UV wave and similar reduction of the bacteria. More future work would be done about the mentioned phenomenon.
Fig. 3. the bacteria concentration and decontaminated efficiency at the exposure of different irradiation time.
3.3. Effect of installation height on the decontaminated efficiency of bacteria Without the irradiation of UV, the background concentration were gained by function 1 as 440±132, 1258±676 and 1132±132 CFU/m3 at the installation height of 1.8m, 2.0m and 2.2 m respectively. Irradiated for 30min, the bacteria counts reduced to 282±70, 817±358 and 1037±179 CFU/m3 at three heights (Fig. 4). While the UV lamp was installed at the height of 1.8m and 2.0 m, the best reduced efficiency of the bacteria (more than 35%) has obtained in the study (Fig. 4). At the height of 2.2 m, the effect of sterilization of UV lamp is poor (less than 10%). Increasing of irradiation distance, the better sterilization effects were gained. With the installation height over a certain range, the poor influence had been gained on the bacteria by the UV wave.
Fig. 4. the bacteria concentration and decontaminated efficiency with the different installation height.
4. Conclusions Analyzing the experimental results, some conclusions were made as follows. (1) When the UV power selected as 20w, 30w and 40w, the sterilization effect were sequentially obtained from the experiments. Considering the type of ultraviolet germicidal lamp in the markets, the UV device of 40W was suggested as better one. (2) The experimental results showed that the ultraviolet germicidal lamp is turned on, sterilization effect is most obvious at the continuous
1380
Yanju Li et al. / Procedia Engineering 205 (2017) 1376–1380 Yanju Li et al / Procedia Engineering 00 (2017) 000–000
5
irradiated for 60 min. And when the irradiation time continue to lengthen; sterilization effect has no obvious change with increasing power consumption. (3) Seen from the experimental results, the lower the installation height, the better sterilization effect at the installation height of 1.8 m and 2.0 m. For the sterilization effect, dining room space, decoration and security factors such as teachers and students, it is suggested that ultraviolet germicidal lamp should be installed at height of about 2.0 m. Acknowledgements This work was financially supported by the National Students' innovation and entrepreneurship training program (201610792007) and Students' innovation and entrepreneurship training programs of Tianjin Chengjian university (201710792058). References [1] B Fu, H Zhao, B Yong, et al. Public air microbial contamination research progress, Chin J Public Health, 28 (6) (2012) 857–858. [2] D Yu, L Ye, M Cheng, et al. Investigation of Pollutant Airbone Microbes in Campus, J Prev Med Inf, 27(10) (2011)766–769. [3] Bluyssen PM, Cox C, Seppanen O, et al. Why，when，how do HVAC-systems pollute the indoor environment and what to do about it? the European AIRLESS project, Build Environ. 38 (2003) 209–225. [4] Harstad, J.B., Decker, H.M., Wedum, A.G.. Use of ultraviolet irradiation in a room air Conditioner for removal of bacteria, Applied Microbiology, 2 (1954) 148–151. [5] Tseng, C.C., Li, C.S.. Inactivation of virus-containing aerosols by ultraviolet germicidal irradiation, Aerosol Sci Tech. 39 (2005) 1136–1142. [6] Linnes J C, Rudnick S N, Hunt G M, et al. Eggcrate UV: a whole ceiling upper-room ultraviolet germicidal irradiation system for air disinfection in occupied rooms, Indoor air. 24(2) (2014) 116–124. [7] Memarzadeh F, Olmsted R N, Bartley J M. Applications of ultraviolet germicidal irradiation disinfection in health care facilities: effective adjunct, but not stand-alone technology, Am J Infect Control. 38(5) (2010) S13–S24. [8] J Ke W Li, Y Chen. Study on disinfection efficiency by ultraviolet. Journal of environmental pollution and control. 25(3) (2003),136–138,144. [9] Kujundzic, E., Matalkah, F., Howard, C.J., Hernandez, M., Miller, S.L. UV air cleaners and upper-room air ultraviolet germicidal irradiation for controlling airborne bacteria and fungal spores, J Occup Environ Hyg. 3 (2006) 536–546. [10] Xu, P., Kujundzic, E., Peccia, J., Schafer, et al. Impact of environmental factors on efficacy of upper-room air ultraviolet germicidal irradiation for inactivating airborne mycobacteria, Environ Sci Technol. 39 (2005) 9656–9664. [11] Sung M, Kato S. Estimating the germicidal effect of upper-room UVGI system on exhaled air of patients based on ventilation efficiency, Build Environ. 46 (11) (2011) 2326–2332. [12] Y Li, S Zhao, D Niu, et al. Investigation on the usage situation of ultraviolet disinfection devices installed at university canteen. Chinese journal of disinfection. 26(2017) 145–147. [13] X Yu . Modern air microbiology. Beijing, people's military medical press. (2002)181–188. [14] Hayleeyesus S F, Ejeso A, Derseh F A. Quantitative assessment of bio-aerosols contamination in indoor air of University dormitory rooms, International Journal of Health Sciences. 9(3) (2015) 249–256.