Indoor air
biocontamination
133
Environmental Management and Health, Vol. 11 No. 2, 2000, pp. 133-138.#MCBUniversity Press, 0956-6163
Received 5 March 1999 Accepted 12 June 1999
An initial control of indoor air
biocontamination
Kamal T. Hindy and Abdel Hameed A. Awad
Air Pollution Department, National Research Centre,Dokki, Giza, Egypt
Keywords Pollution, Contamination, Health
Abstract Indoor biocontamination is recognized as a potential public health problem.The concentration of indoor pollutants is varied, depending on air filtration, air distribution systems and air cleaning devices.One portable air cleaning device, ``Ionizer Air clean-er/Air clinic'' was investigated.The ability of particles to remain airborne or pass through filters depends on the size and density of particles.Air clinic device removed bacterial and mould contaminants in efficiencies up to 98.7 per cent and 67 per cent respectively, after 30 minutes of operation. After purification,Penicilliumspecies were predominant.Small particles (4m) are passed through
filter mates.The negative ions produced by the device are effective for removing suspended particulates in efficiency up to 99 per cent.The disadvantages of this device are: the need to change the filter after short period of operation, and the unpleasant odour emitted from the device during operation due to ionization of particles.
Introduction
Several pollutants from indoor sources affect human health. Microorganisms, pollen, dust, animal dander, mists, gases and vapour arise inside buildings and need to be removed (Cox, 1987). Many purification processes are used for indoor pollution control. These are: aerosol removal and inactivation; adsorption of odour; absorption of gases and vapour; and air ions and charged particles. Moreover many air cleaning devices such as electrostatic precipitation, air filters, scrubbers and odour absorbed bed are effective for removing contamination (Cox, 1987).
Filtration technique is widely applied for removing particulates (Darlow, 1973). Particulates of about 0.2-0.3m diameter are less impacted on filters.
Absolute or HEPA (high efficiency particulate air) filter are most effective for removing microorganisms (Sivinski, 1968). However, many strong germicidal agents such as ethanol, chlorine, sodium hypochlorite, formaldehyde and ozone are used for air purification (Williams and Gotass, 1992; Beebyet al., 1967).
The primary objective of the present study is directed towards investigation of the efficiency of a portable air purification device for initial removing of viable particulates, to prevent human health effects.
Material and methods
Experimental room
An experimental room (ER), (3m wide; 4m long and 5m high) resembling a residential and workplace indoor environment was chosen for this experiment. The ER is tightly sealed and not equipped with heating, ventilation and air conditioning systems.
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Purification device
Ionizer air cleaner, multistage filtering system (commercially known as air clinic) was investigated. This device consists of electrostatically changed microfilter; activated charcoal filter; and electrostatic ionizer , produces much -ve ions (Figure 1).
The air clinic device was operated at a room temperature (28-30oC) with an air flow rate of 195m3/h (3.25m3/min) which resulted in approximately three exchanges of room air volume per hour.
Target organisms and sampling devices
Dust was distributed from walls and floor and allotted 30 minutes to equilibrate the room air. Before purification, dust and bio-aerosol samples were collected for bacteria and molds. Bioaerosol samples were collected by using liquid impinger sampler containing 50ml, buffer phosphate (Difco), and a calibrated vacuum pump to draw air at 12.5l/min, for 15 minutes. Open plates (100mm diameter) were placed for five minutes at a position of 1.5m high, from the floor. Swab samples were collected from walls, floors, outer and inner sides of filter mates. This series of experiments was repeated after the room was purified at interval times. The swabs were collected after 30 minutes of operation.
Microbial analysis
The swabs were eluted in 10ml phosphate buffer. Trypticase soy agar and malt extract agar (Difco) media were used to quantitate the airborne bacteria and moulds, respectively. Spread plate technique was used for inoculation. The plates were incubated at room temperature (25-30oC) for 72 hrs. The colonies were counted and expressed as colony forming unit (cfu) .
Filter Inlet
On – Off Outlet
Figure 1.
Indoor air
biocontamination
135
Results and discussion
The density of suspended dust, as well as the concentrations of bioaerosol and settled particulate collected before and after purification, are shown in Table I. It can be seen from the presented data that, the levels of saprophytic bacteria and mould counts were significantly reduced after purification. The device efficiencies for bacterial removing reached 23 per cent, 63 per cent and 98.7 per cent after 5, 15 and 30 minutes of operation respectively. On the other hand, the moulds levels were significantly decreased after five minutes (efficiency 89 per cent). However, the mould levels were increased again, and the efficiencies were decreased to 57 per cent and 67 per cent after 15 and 30 minutes, respectively. It is suggested, therefore, that the mould spores are attracted on the filter mats by the electrostatic character immediately after operation. After saturation of filters, mould spores (spore sizes <4m) can penetrate the filter mates easily,
with the action of air flow force and pressure drop at the filter. Noble and Clayton (1963) found fungi in air as single spores. In addition, Spengler and Sexton (1983) reported that, purification of air by gas adsorbers, air filters and electrostatic precipitators is efficient for removing dust particulates, tobacco smoke and biological particulates (not single cells). Bacteria are found in air as clusters or larger particles (Southey and Harper, 1971). Cladosporium spores are clustered in small chain whereas Penicillium and Aspergillus spores are more separated, and, Penicillium spores are more isolated particles than the others (Badilletet al.,1987). Also, larger particles have higher momentum than air and can be easily impacted on filters, whereas smaller particles have less momentum than air and able to follow streamlines and the filter pores (Cox, 1987). In addition, fungi spores that are airborne for long times are decreased in size due to dehydration and gravity (Reponenet al., 1992) . Also, Reponenet al. (1994) found fungal spores in the size ranged between 1.1-5.7m indoors. So, it
is suggested that, with time, fungi spores can penetrate filter mates easily.
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After purification, open plate counts were reduced up to 63.5 per cent for bacteria and 60 per cent for fungi. This indicates that, mould spores are lighter (have lower inertial) than bacteria. Swab counts of wall were decreased, whereas, the floor counts were increased (Table II).
This is due to the ionizing wires which produce much - ve ions, and cause the ionization of air molecules (equations 1 and 2). The charged particles react with those of opposite charge. Consequently, particles are aggregated and deposited from wall and air streams leading to an increase in the particulates of surface.
M !M E electron 1
EM !M 2
Table III summarizes the predominant airborne moulds in indoor environment. The predominance of sensitizing moulds (Aspergillus, Cladosporium and
Penicillium) was considered to be significant before purification experiment. The fungal indoor air was composed before experiment from 60 per cent
Penicillium,30percentand10percentAspergillusandCladosporium,respectively. The previous organisms are common in indoor air (Ledford, 1994) and are aeroallergens and may elicit health hazard effects (Leeseet al., 1992; Husman, 1996). Also,PenicilliumandAspergillusoriginated mainly from indoor sources (Flannigan et al. 1991), whereas Cladosporium and yeasts originated mainly from outdoor (Reponen, 1995). Ling-Hung and Terra (1996) found that
Penicillium and Aspergillus versiolor constituted 86 per cent of fungal populations indoors. After purification experiment, mould counts were reduced. Penicillium, Aspergillus and Cladosporium were detected in percentages of 50 per cent, 25 per cent and 25 per cent respectively.
Before purification,Aspergillusspecies constituted 43.7 per cent of total open plate mold spore counts (Table III), whereas, Penicillium spores were the most isolated species (55.5 per cent) after purification. It is suggested, therefore, that
Aspergillus spores (diameter range 3-5 m) have higher inertial force than Penicilliumspores (diameter ranged between 2.5-3.5 (m) (Noble and Clayton, 1963; Reponen, 1995; Abdel Hameed, unpublished data). Moreover, gravity has eliminated the larger particles and reduced the chance of increasing the particles which carry viable organisms with the size increase (Nobleet al., 1963).
Table II.
The levels of microorganisms on swabs before and after purification
Location Bacteria Moulds
Before purification
Wall 15cfu/ml 0
Floor 15cfu/ml 0
After purification
Wall 5cfu/ml 0
Indoor air
biocontamination
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Aspergillus species were settled rapidly and impacted by filter mats, whereas
Penicillium have small inertial force, need a long time to be settled, and can penetrate filter mats. The settling velocity of particles is a function of the squared diameter. So, larger particles fall down faster than smaller ones (Reponen, 1995). Paratet al. (1996) found that the efficiency of the air conditioning filters are 36 per cent for Penicillium and 70 per cent for Aspergillus and Cladosporium. They found also that,Penicilliumconcentration below the filter mat is greater than that above the filter mat and the filters have a low efficiency for collecting this type of fungus. In confirmation of these results, Penicillium species were only isolated from the inner surface of the filter mats (Table IV). So, this indicates that, the air clinic device is not highly efficient for < 4m mold spores and lack sensitivity for
collection of particles in the Penicillium range sizes. Buttner and Stetzenbach (1993) recordedPenicilliumthrough HEPA filter. Consequently, the health risks were reduced, due to, low mould exposures.
Conclusions
Many aerial disinfectant agents are used for air cleaning and purification. Most chemical disinfectants have harmful effects. The mechanical, multistage filtering system under investigation was very efficient for removing bacteria but has less efficiency for mould, especially for4m spores. So, if dry filters were changed
with viscous or HEPA filters, it is expected that the efficiency will be increased. However, with good ventilation and behaviour adjustments, it is easy to keep rooms clean, without using any purification device.
Table III.
Predominant airborne moulds isolated from bioaerosols samples
Sampler Mold counts Aspergillus%a Cladosporuim%a Penicillium%a
Before purification
Liquid impinger 1.333104* 30 10 60
Open plates 16** 43.75 25 31.25
Membrane filter
technique 50*** 50 0 50
After purification
Liquid impinger 5.3103* 25 25 50
Open plates 9** 33.3 11.2 55.5
Membrane filter
technique 40*** 75 0 25
Notes:a= Percentage of total isolated molds; * = cfu/m3; ** = cfu/plate; *** = cfu/ml
Table IV.
Predominant moulds isolated from outer and inner sides of filter mats
Mat side Count Penicillium(%) Aspergilluzs(%)
Outer 50* 90 10
Inner 15* 100 0
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