aereobiological enginnering topics - pennsylvania
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COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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AEREOBIOLOGICAL ENGINNERING TOPICS
COLLEGE OF ENGINEERING
PENNSYLVANIA STATE UNIVERSITY
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TABLE OF CONTENTS
PART 1 - AIRBONE PATHOGENS 3
1 – AIRBONE PATHOGENS DATABASE 3
2 – LIST OF AIRBONE PATHOGENS 4
PART 2 - AIRBONE PATHOGEN CONTROL TECHNOLOGIES 6
3 - AIRBONE PATHOGEN CONTROL TECHNOLOGIES LIST 6
4 – DESCRIPTION OF CURRENT AIRBONE PATHOGEN
CONTROL TECHNOLOGIES 7
4.1 - ISOLATION SYSTEMS 7
4.2 – AIR FILTRATION 13
4.3 – ULTRAVIOLET IRRADATION 20
4.4 – OUTDOOR AIR PURGIN 26
4.5 - ELECTROSTATIC PRECIPITATION 33
4.6 – NEGATIVE AIR IONIZATION 35
4.7 – VEGETATION 39
5. DESCRIPTON OF DEVELOPMENTAL AIRBONE PATHOGEN
CONTROL TECHNOLOGIES 42
5.1 – PHOTOCATALYTIC OXIDATION 42
5.2 – AIR OZONIZATION 43
5.3 –CARBON ADSORTION 47
5.4 – PASSIVE SOLAR EXPOSURE 48
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5.5 – PULSED LIGHT 51
5.6 – ULTRASONIC ATOMIZATION 59
5.7 – MICROWAVE ATOMIZATION 60
PART 3 – PUBLICATONS 62
PUBLICATIONS DOWNLOAD 62
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PART 1 - AIRBONE PATHOGENS
1 – AIRBONE PATHOGENS DATABASE
Viruses
Bacteria
Fungi
List of Airborne Pathogens
VIRUSES
Orthomyxoviridae - Influenza
Arenavirus - Junin
Arenavirus - Machupo
Arenavirus - Lassa
Filovirus - Marburg
Filovirus - Ebola
Hantaviruses
Picornoviridae - Rhinoviruses
Picornoviridae - Echovirus
Coronaviruses
Paramyxovirus
Morbillivirus
Respiratory Synctial Virus
Togavirus
Coxsackievirus
Parvovirus B19
Parainfluenza
Adenoviruses
Reoviruses
Poxvirus - Variola
Poxvirus - Vaccinia
Varicella-zoster
BACTERIA
Neisseria meningitidis
Klebsiella pneumoniae
Pseudomonas aeruginosa
Pseudomonas
pseudomallei
Pseudomonas
mallei
Acinetobacter
Moraxella
catarrhalis
Moraxella
lacunata
Alkaligenes
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Cardiobacterium
Haemophilus
influenzae
Haemophilus
parainfluenzae
Bordetella
pertussis
Francisella
tularensis
Legionella
pneumophila
Chlamydia psittaci
Chlamydia
pneumoniae
Mycobacterium
tuberculosis
Mycobacterium
kansasii
Mycobacterium
avium-intracell.
Nocardia asteroides
Bacillus anthracis
Staphylococcus
aureus
Streptococcus
pyogenes
Streptococcus
pneumoniae
Corynebacteria
diphtheria
Mycoplasma
pneumoniae
FUNGI
Aspergillus spp.
Absidia corymbifera
Rhizopus stolonifer
Mucor plumbeus
Cryptococcus
neoformans
Histoplasma
capsulatum
Blastomyces
dermatitidis
Coccidioides immitis
Penicillium spp.
Micropolyspora faeni
Thermoactinomyces vulgaris
Alternaria
alternata
Cladosporium spp.
Helminthosporium
Stachybotrys spp.
2 – LIST OF AIRBONE PATHOGENS
BACTERIA DISEASE / SYMPTOM TYPE MIN DIA. microns SHAPE
Neisseria meningitidis meningitis gram- - cocci
Klebsiella pneumoniae pneumonia gram- 0.4 rods
Pseudomonas aeruginosa pneumonia gram- 0.5 rods
Pseudomonas pseudomallei pneumonia gram- 0.5 rods
Pseudomonas mallei pneumonia gram- 0.5 rods
Acinetobacter pneumonia gram- 0.5 cocci
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Moraxella catarrhalis - gram- 0.5 cocci
Moraxella lacunata - gram- 0.5 cocci
Alkaligenes - gram- - -
Cardiobacterium - gram- - -
Haemophilus influenzae flu gram- 1 rods
Haemophilus parainfluenzae flu gram- 1 rods
Bordetella pertussis whooping cgh gram- 0.5 cocci
Francisella tularensis pneum./fever gram- - cocci
Legionella pneumophila Legionnaires gram- 0.5 rods
Chlamydia psittaci pneumonia gram- 1 -
Chlamydia pneumoniae pneumonia gram- 1 -
Mycobacterium tuberculosis TB gram+ 0.2 rods
Mycobacterium kansasii (TB) gram+ 0.2 rods
Mycobacterium avium-intracell. pneumonia gram+ 0.2 rods
Nocardia asteroides pneumonia gram+ - rods
Bacillus anthracis anthrax gram+ - cocci
Staphylococcus aureus pneumonia gram+ - cocci
Streptococcus pyogenes scarlet fever gram+ 0.5 cocci
Streptococcus pneumoniae pneumonia gram+ 0.5 cocci
Corynebacteria diphtheria diptheria gram+ - rods
Mycoplasma pneumoniae pneumonia no wall 0.2 coccoid
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PART 2 - AIRBONE PATHOGEN CONTROL TECHNOLOGIES
3 - AIRBONE PATHOGEN CONTROL TECHNOLOGIES LIST
3.1 - CURRENT
A. Isolation Systems
B. Air Filtration
C. Ultraviolet Irradiation
D. Outdoor Air Purging
E. Electrostatic Precipitation
F. Negative Air Ionization
G. Vegetation
3.2 - DEVELOPMENTAL
A. Photocatalytic Oxidation
B. Air Ozonation
C. Carbon Adsorption
D. Passive Solar Exposure
E. Ultrasonic Atomization
F. Microwave Atomization
G. Pulsed Light
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4 – DESCRIPTION OF CURRENT AIRBONE PATHOGEN CONTROL
TECHNOLOGIES
4.1 - ISOLATION SYSTEMS
ISOLATION ROOMS & PRESSURIZATION CONTROL
Isolation systems can be classified in three basic categories :
Negative Pressure Isolation Rooms
Positive Pressure Isolation Rooms
Multi-level Biohazard Laboratories
Also, dual-purpose systems now exist that can be controlled to serve as either
negative pressure or positive pressure isolation rooms. The isometric view shown
below illustrates the basic design principle for pressure control of isolation rooms. It
includes an ante room for separating the isolation room from the corridor of the
facility. In this diagram, air is supplied to the isolation room and exhausted from both
the isolation room and the ante room. The balance of airflow, or the difference
between between supply and exhaust, will dictate whether the room experiences
positive or negative pressure with respect to ambient.
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In this diagram, air would flow between the isolation room and the ante room, mostly
through the gaps in and around the door. For a positive pressure room the air would
flow from the isolation room to the ante room, where it would be exhausted partly by
the exhaust duct and partly by flowing out to the corridor. In a negative pressure
room, air would flow from the ante room to the isolation room. Pressure control is
maintained by modulating the main supply and exhaust dampers based on a signal
from a pressure transducer located inside the isolation room. This is by no means
the only possible design -- there are various configurations of supply and exhaust
ductwork, dampers and control systems that will accomplish pressurization.
Negative Pressure Isolation Rooms
Negative Pressure Isolation Rooms maintain a flow of air into the room, thus
keeping contaminants and pathogens from reaching surrounding areas. The most
common application in the health industry today is for Tuberculosis (TB) Rooms.
The infectivity of TB is extremely high and these rooms are essential to protect
health workers and other patients.
The CDC recommends 6-12 air changes
per hour (ACH) for TB Rooms. An ante
room is always recommended, as this
provides a barrier between the TB Room
and hallways and limits the impact of
opening doors and traffic. The exhaust air
is normally filtered through a HEPA (High
Efficiency Particulate Air) filter before being
exhausted to the outside, where it is
ultimately rendered harmless by natural elements. Air which is recirculated within
the room is also normally filtered. Ultraviolet Germicidal Irradiation (UVGI),
commonly known as UV light, may be used to augment HEPA filters, but cannot be
used in place of HEPA filters, as their effectiveness on airstreams is limited.
The exact air pressure differential which is required to be maintained is nominal
only, as it merely indicates the airflow direction. It is sometimes stated as 0.001"wg,
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but this is not a pressure which is practical to measure, and therefore other criteria
are given such as maintaining an inward velocity of 100 fpm, or exhausting 10% of
the airflow, or exhausting 50 cfm more than the supply. The exact criteria will always
be dependent on both the size and the airtightness of the subject facility.
Positive Pressure Isolation Rooms
Positive Pressure Isolation Rooms maintain a flow of air out of the room, thus
protecting the patient from possible contaminants and pathogens which might
otherwise enter. The most common application today is HIV Rooms and rooms for
patients with other types of immunodeficiency. For such patients it is critically
important to prevent the ingress of any pathogens, including even common fungi
and bacteria which may be harmless to
healthy people.
Design criteria for HIV Rooms are similar to
those for TB Rooms. Air supplied to or
recirculated in HIV Rooms is normally
filtered through HEPA filters, and UVGI
systems are sometimes used in conjunction
with these. Anterooms are recommended
and the air pressure differential criteria as
described for TB Rooms applies similarly.
Approximately 15% of AIDS patients also suffer from TB, and this presents a unique
design problem. One solution is to house the positive pressure (HIV) room within a
negative pressure (TB) room, or vice-versa, which would be similar to a pair of
nested biohazard levels. A much less expensive alternative is to design an entire
house or building as a positive pressure (HIV) room, and this makes the outdoor air
play the part of the second pressure barrier as it will effectively sterilize any exiting
pathogens. Exhaust HEPA filters are still recommended, however, to protect any
passersby.
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Pressurization Control in Buildings
The basic principle of pressurization for microbial contaminant control is to supply air
to areas of least contamination (greatest cleanliness) and stage this air to areas of
progressively greater contamination potential. It could be assumed that in non-
biohazard facilities, the exhaust or exfiltration from the building could go directly to
the outside. In medical facilities, like TB clinics, this air is often HEPA filtered and
sometimes given UVGI exposure before exhausting to the outside, though the
reasons for this are primarily because of litigation concerns and not based on any
known realities.
An alternate perspective on the design principle of pressurization control is to
exhaust air from those areas which have the greatest contamination potential, and
allow air to be staged, or cascaded, from progressively cleaner areas, or the areas it
is desired to protect. Systems which combine both negative pressurization in
contaminated areas with positive pressurization in clean, or protected, areas will
have the greatest degree of protection and control. Below is an illustration of the
basic principle of cascading airflows from clean areas to areas of progressively
greater microbial conatmination potential.
In the above diagram, a facility is depicted which has offices and isolation rooms,
separated by corridors and other areas (storage rooms, labs). Air is supplied to the
areas, usually offices, maintained at the greatest positive pressure (marked with a
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'++'), and exhausted from the areas maintained at the greatest negative pressure
(marked with a '- -'). Transfer air (exfiltration/infiltration) is identified with purple arrows.
This represents one possible arrangement, but facilities often differ markedly in
layouts, and the presuurization scheme must be adapted individually for each facility.
The unlabeled rooms in the diagram above could be laboratories, which usually have
independently operating exhaust hoods or separate ventilation systems. If not, they
would be generally be designed as double negative pressurization areas.
Biohazard Laboratories
Biohazard laboratories are merely isolation rooms with strict requirements defining
their degree of airtightness, pressurization and associated equipment. There are
four biohazard levels, in level 1 defines a simple isolated area, and in which level 4
defines a near perfectly airtight zone requiring breathing apparatus and airtight
anterooms or staging areas. Specific information on laboratory design is widely
available from various sources, including ANSI, ASHRAE and the CDC.
Bibliography
1. ANSI (1992). American national standard for laboratory ventilation. New York,
American National Standards Institute.
2. AIA (1993). Guidelines for construction and equipment of hospital and medical
facilities. Mechanical Standards. American Institute of Architects. Washington.
3. ASHRAE (1991). Health Facilities. ASHRAE Handbook of Applications. ASHRAE.
Atlanta.
4. ASHRAE (1996). Designing HVAC systems for hospital isolation rooms. ASHRAE
Short Course. Atlanta, ASHRAE.
5. Bartholomew, D. (1994). “TB control in hospitals.” Engineered Systems July: 52-53.
6. Bloom, B. R. (1994). Tuberculosis : Pathogenisis, Protection, and Control.
Washington, ASM Press.
7. Blowers, R. and B.Crew (1960). “Ventilation of operating-theatres.” Journal of
Hygiene 58: 427-448.
8. Brief, R. S. and T. Bernath (1988). “Indoor pollution: guidelines for prevention and
control of microbiological respiratory hazards associated with air conditioning and
ventilation systems.” Appl. Indust. Hyg. 3: 5-10.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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9. CDC (1994). Guidelines for preventing the transmission of Mycobacterium
tuberculosis in health-care facilities. Federal Register. CDC. Washington, US Govt.
Printing Office. 59.
10. Galson, E. and K. Goddard (1968). “Hospital air conditioning and sepsis control.”
ASHRAE 10(7): 33-41.
11. Galson, E. (1987). “Facility microbiological test procedures.” ASHRAE Transactions
93(1): 1289-1303.
12. Galson, E. and J. Guisbond (1995). “Hospital sepsis control and TB transmission.”
ASHRAE May.
13. Gill, K. E. (1994). “HVAC design for isolation rooms.” HPAC July: 45-52.
14. Greene, V. W., D. Vesley, et al. (1960). “The engineer and infection control.”
Hospitals 34: 69-74.
15. Hers, J. F. P. and K. C. Winkler (1973). Airborne Transmission and Airborne
Infection. VIth International Symposium on Aerobiology, Technical University at
Enschede, The Netherlands, Oosthoek Publishing Company.
16. ICCCS (1992). The Future Practice of Contamination Control. Proceedings of the
11th International Symposium on Contamination Control, Westminster, Mechanical
Engineering Publications.
17. Kunkle, R. S. and G. B. Phillips (1969). Microbial Contamination Control Facilities.
New York, Van Nostrand Reinhold.
18. Lidwell, O. M. and R.E.O.Williams (1960). “The ventilation of operating-theatres.”
Journal of Hygiene 58: 449-464.
19. Lidwell, O. M. (1960). “The evaluation of ventilation.” J. Hygiene 58: 297-305.
20. Linscomb, M. (1994). “AIDS clinic HVAC system limits spread of TB.” HPAC
February.
21. Maloney, S. A., M. L. Pearson, et al. (1995). “Efficacy of control measures in
preventing nosocomial transmission of multidrug-resistant tuberculosis to patients
and health care workers.” Annals of Internal Medicine 122(2): 90-95.
22. Miller-Leiden, S., C. Lobascio and W.W.Nazaroff (1996). “Effectiveness of in-room
air filtration and dilution ventilation for tuberculosis infection control.” Journal of the
Air and Waste Management Association 46(9): 869.
23. Riley, R. L. and F. O'Grady (1961). Airborne Infection. New York, The Macmillan
Company.
24. Rubbo, S. D., T. A. Pressley, et al. (1960). “Vehicles of transmission of airborne
bacteria in hospital wards.” The Lancet 7147: 397-400.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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25. Seagal-Maurer, S. and G. E. Kalkut (1994). “Environmental control of tuberculosis:
Continuing controversy.” Clinical Infectious Diseases 19: 299-308.
26. Sullivan, J. F., J.R.Songer (1966). “Role of differential air pressure zones in the
control of aerosols in a large animal isolation facility.” Applied Microbiology 14(4):
674-678.
27. Wedum, A. G. (1961). “Control of laboratory airborne infection.” Bacter. Rev. 25:
210-216.
28. Weinstein, R. A. (1991). “Epidemiology and control of nosocomial infections in adult
intensive care units.” The American Journal of Medicine 91(suppl 3B): 179S-184S.
29. Winters, R. E. (1994). “Guidelines for preventing the transmission of tuberculosis: A
better solution?” Clinical Infectious Diseases 19: 309-310.
4.2 – AIR FILTRATION
FILTRATION OF MICROORGANISMS
Three types of filters exist for use in ventilation systems, prefilters,
HEPA (High Efficiency Particulate Air) filters and ULPA filters. A
typical HEPA filter, such as the one shown at
right will filter micron sized particles at about 95%
efficiency. Some box or pleated type filters can be
as thin as 2-4 inches, or as wide as 8-12 inches.
The picture at the right shows a bag type HEPA filter, which can
extend up to 24 inches. Bag type filters typically have a lower pressure drop than the
pleated or box type HEPA. The picture below shows a typical installation with a bank
of prefilters at the outside air inlet of a large air handling unit. These prefilters are
typically between 70-90% efficient.
Prefilters and HEPAs, whether bag or box type, will filter particles down to below 1
micron in size, but with varying efficiencies. Different
filters have different pressure drop characteristics, which
is a factor in energy and cost analysis. HEPA filters are
comonly found in hospital isolation rooms, operating
theaters, and Level 3 & 4 containment facilities, as well
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as in industrial clean rooms.
HEPA filters are typically rated as 99.97% effective in removing dust and particulate
matter above 0.3 micron in size, based on DOP (diocytl phthalate) testing usually
performed by the manufacturer. In theory, HEPA filters should be highly effective
against bacteria and fairly effective against viruses, but real world installations do
not always achieve perfomance limits measured in laboratories.
Air Filtration - Theory and Application
HEPA filters consist of fine fibers as illustrated in the diagram at the right. Materials
vary, but generally these are made of
synthetic fibrous materials. The
principle of HEPA filtration is not to
restrict the passage of particulate by
the gap between fibers, but by
altering the airflow streamlines. The
airflow will slip around the fiber, but
any higher-density bioaerosols or
particulate matter will not change
direction so rapidly and, as a result of
their inertia, will tend to impact the fiber. Once attached, most particulates will not be
re-entrained in the airstream.
In the diagram below, the airstream is depicted winding its way around a single fiber.
The heavier particulates will either impact the fiber directly, or sometimes attach by
close passage, due to static electrical attraction, or simply by physical attachment.
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The following diagram shows the effects of Brownian motion on particles
approaching molecular dimensions. Viruses can be small enough to be dominated
by Brownian motion as opposed to gravity or inertial forces.
Some early studies found HEPA filters could remove bacterial spores at 99.9999 %
efficiency and viruses at 99.999% efficiency (Harstad 1969, Thorne 1960), but this
was under ideal laboratory conditions. The Harstad study noted that manufacturer's
quality control had the most significant effect on filter performance, and that even a
single pinhole could seriously affect filter efficiency. Also, operating outside design
conditions of airflow or humidity could multiply the amount of virus penetration.
An additional factor that can have a major impact on filter performance is the
installation and maintenance of the filters. Poor tolerances in the fit of the filters to
the frames can seriously degrade performance by bypassing unfiltered air. In
applications that demand high performance levels, such as the nuclear industry and
clean room technology, DOP testing is performed with in-place filters. The testing
determines the presence of leaks in the filters or frames, mixing uniformity, and
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airflow, but does not determine actual filter efficiency (Ornberg 1978, US NRC Reg.
Guide 1.52 & 1.140). It is assumed that if all these other conditions are met, filter
efficiency will approach that obtained in the factory, or 99.97 % at 0.3 microns.
Achieving all the requirements for acceptable operation often yields only borderline
results.
No formal studies exist in which actual HEPA filter installations (for humans) have
been put to the test with live viruses and bacteria, and therefore quantitative data on
real-world efficiencies are unavailable. There have been reports of tuberculosis
bacilli (1 - 5 micron rod-shaped bacteria) penetrating HEPA filters in treatment
facilities. It is entirely possible that bacteria of this size may pass through HEPA
filters due to the fact that they are dynamic living organisms that do not wish to
remain attached to dry surfaces without nutrients.
Viruses can be much smaller than 0.3 micron and although HEPA filters can
theoretically remove particles down to about 0.01 microns in size, their performance
is nonlinear and the efficiency drops off sharply at this size. As has been pointed out
by some biologists, the use of HEPA filters may provide evolutionary pressure for
smaller microorganisms.
Office buildings, schools and other such facilities do not normally include HEPA
filters in the ventilation system, although they often include pre-filters and filters of
lower efficiencies. The addition of HEPA filters to standard building systems may
have a significant effect on the reduction of airborne bacteria, viruses and fungi, as
well as other particulates. The overall effectiveness of such an approach, and
economic comparisons with other methods for controlling airborne pathogens, is
currently being studied at Penn State through the use of computer models. The
construction of a model HEPA filter bank, and testing of filtration efficiencies with live
bacteria and viruses, is being planned for the Spring semester of 1997. Updates of
progress and results will be reported here.
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COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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carinii DNA by filtration of air." Scandinavian Journal of Infectious Diseases 28: 279-
282.
26. Ornberg, S.C. (1978). Design, Construction and Testing of Nuclear Air Cleaning
Systems, Rev. 0, Dated 10-2-78. Sargent & Lundy Engineers, Chicago.
27. Pollman, R. A. (1990). "A new technology in the practical application of sterile air
and gas filtration for the brewing process." Brewers Digest 65(4): 33-35.
28. Putensen, C., J. Rasanen, & F. A. Lopez (1995). "Interfacing between spontaneous
breathing and mechanical ventilation affects ventilation-perfusion distributions in
experimental bronchoconstriction." American Journal of Respiratory Crit Care Med
151: 993-999.
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29. Reinhart, A., and H.Tammet (1995). "Electrical simulation of aerosol deposition in
lungs." Journal of Aerosol Science 26(S1): s613-s614.
30. Reponen, T., M.Lehtonen and T.Raunemaa (1992). "Effect of indoor sources on
fungal spore concentration and size distribution." Journal of Aerosol Science 23(S1):
s663-s666.
31. Rothwell, G. (1992). "Collection of airborne microorganisms onto sticky surfaces."
Journal of Aerosol Science 23(S1): s679-s681.
32. Stechkina, I. B., and A.A.Kirsch (1994). "Multistage high efficiency air filtration."
Journal of Aerosol Science 25(S1): s203-s204.
33. Straja, S., and R.T.Leonard (1996). "Statistical analysis of indoor bacterial air
concentration and comparison of four RCS biotest samplers." Environment
International 22(4): 389.
34. Swanson, M. C., A.R.Campbell, M.T. O'Hollaren and C.E.Reed (1990). "Role of
ventilation, air filtration, and allergen production rate in determining concentrations
of rat allergens in the air of animal quarters." American Review of Respiratory
Diseases 141(6): 1578-1581.
35. Tablan, O. C., L.J. Anderson, N.H.Arden, R.F.Beiman, J.C.Butler, M.M.MacNeil and
the HICPAC (1994). "Guideline for the prevention of nosocomial pneumonia."
American Journal of Infect Control 22: 247-292.
36. Thorne, H.V. and T.M. Burrows. (1960). "Aerosol sampling methods for the virus of
foot-and-mouth disease and the measurement of virus penetration through aerosol
filters." Journal of Hygiene 58:409-417.
37. U.S. Nuclear Regulatory Commission, Regulatory Guides 1.52 and 1.140. Design,
Testing and Maintenance Criteria for Air Filtration Units for Nuclear Power Plants.
Code of Federal Regulations 10CFR50.
38. VanOsdell, D. W. (1994). "Evaluation of test methods for determining the
effectiveness and capacity of gas-phase air filtration equipment for indoor air
applications." ASHRAE Transactions 100(2): 511.
39. Wake, D., A.C.Redmayne, A.Thorpe, J.R.Gould, R.C.Brown and B.Crook (1995).
"Sizing and filtration of microbiological aerosols." Journal of Aerosol Science 26(S1):
s529-s530.
40. Watanabe, T., F.Tochikubo, J.Hautanen and E.I.Kauppinen (1995). "Review of
particle agglomeration." Journal of Aerosol Science 26(S1): s19-s20.
41. Wathes, C. M., H.E.Johnson and G.A.Carpenter (1991). "Air hygiene in a pullet
house: effects of air filtration on aerial pollutants measured in vivo and in vitro."
British Poultry Science 32: 31-46.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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42. Weinstein, R. A. (1991). "Epidemiology and control of nosocomial infections in adult
intensive care units." The American Journal of Medicine 91(suppl 3B): 179S-184S.
43. Willeke, K., S.A/.Grinshpun, V.Ulevicius, S.Terzieva, J.Donnelly, S.Stewart and
A.Jouzaitis (1995). "Microbial stress, bounce and re-aerosolization in bioaerosol
samples." Journal of Aerosol Science 26(S1): s883-s884.
4.3 – ULTRAVIOLET IRRADATION
ULTRAVIOLET GERMICIDAL IRRADATION
The use of ultraviolet
germicidal irradiation
(UVGI) for the
sterilization of
microorganisms has
been studied since
the 1930s. Microbes are uniquely vulnerable to the effects of light at wavelengths at
or near 2537 Angstroms due to the resonance of this wavelength with molecular
structures. Looking at it another way, a quanta of energy of ultraviolet light
possesses just the right amount of energy to break organic molecular bonds. This
bond breakage translates into cellular or genetic damage for microorganisms. The
same damage occurs to humans, but is limited to the skin and eyes.
The ultraviolet component of
sunlight is the main reason
microbes die in the outdoor air.
The die-off rate in the outdoors
varies from one pathogen to
another, but can be anywhere from
a few seconds to a few minutes for
a 90-99% kill of viruses or contagious bacteria. Spores, and some environmental
bacteria, tend to be resistant and can survive much longer exposures. UVGI
systems typically use much more concentrated levels of ultraviolet energy than are
found in sunlight.
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Some properly designed, and well-maintained, UVGI installations have proven
highly effective, as in certain hospitals, and some studies perfomed in schools. CDC
guidelines recommend the use of UVGI only with the simultaneous use of HEPA
filters and high rates of purge airflow. The germicidal effects can also be species-
dependent.
Laboratory tests have achieved extremely high rates of mortality under idealized
conditions. In actual applications, many factors can alter the effectiveness of UVGI,
including the following :
Exposure time (the air velocity must allow for a sufficient dose).
Room air mixing (for non-powered applications like ceiling units).
Power levels.
The presence of moisture or particulates provide protection for microbes.
Dust settling on light bulbs can reduce exposures, maintenance is necessary.
One especially effective application of UVGI is the control of microbial growth in air
handling unit cooling coil and filter assemblies. The constant exposure has been
found to be very effective at controlling fungal growth, either because the spores are
inactivated, or perhaps because mycelial growth cannot be sustained under
continuous exposure.
Certain types of UVGI designs seem to provide a much higher rate of disinfection
than standard models operating at nearly identical spectrums, the difference being
the result of improvements in the electrical power controls and regulation of internal
plasma temperature, resulting in the generation of a more constant energy density
at a distance from the light source.
Viruses are especially susceptible to UVGI, more so than bacteria, but are also very
difficult to filter. Some studies have shown that viruses are more sensitive to
ultraviolet radiation at wavelengths somewhat above the normal UVGI broad-band
wavelength of 2537 A (Rauth 1965; Setlow 1961). A combination of filtration for
bacteria and spores, with UVGI for viruses may be an optimum combination if all
components are sized appropriately.
UVGI Theory & Rate Constants for Airborne Pathogens
UVGI inactivates pathogens according to the standard decay equation
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S = exp(-kIt)
In this equation S represents the fraction of the original population that survives
exposure at time t, and I represents the UVGI intensity. The rate constant k has
been determined experimentally for a number of bacteria, viruses and spores, at
different power levels. See Mathematical Modeling of Ultraviolet Germicidal
Irradiation for Air Disinfection by Kowalski et al 2000 for a summary of most of
the known rate constants for the indicated pathogens.
References
1. Abshire, R. L. and H. Dunton (1981). "Resistance of selected strains of
Pseudomonas aeruginosa to low-intensity ultraviolet radiation." Appl. Envir. Microb.
41(6): 1419-1423.
2. Allegra, L., F. Blasi, et al. (1997). "A novel device for the prevention of airborne
infections." J. Clinical Microb. 35(7): 1918-1919.
3. Antopol, S. C. and P. D. Ellner (1979). "Susceptibility of Legionella pneumophila to
ultraviolet radiation." Appl. & Environ. Microb. 38(2): 347-348.
4. Beebe, J. M. (1958). "Stability of disseminated aerosols of Pastuerella tularensis
subjected to simulated solar radiations at various humidities." Journal of
Bacteriology 78: 18-24.
5. Collier, L. H., D. McClean, et al. (1955). "The antigenicity of ultra-violet irradiated
vaccinia virus." J. Hyg. 53(4): 513-534.
6. Collins, F. M. (1971). "Relative susceptibility of acid-fast and non-acid fast bacteria
to ultraviolet light." Appl. Microbiol. 21: 411-413.
7. Darken, M. A. and M. E. Swift (1962). "Effects of ultraviolet-absorbing compounds
on spore germination and cultural variation in microorganisms." Applied
Microbiology 11: 154-156.
8. David, H. L. (1973). "Response of mycobacteria to ultraviolet radiation." Am. Rev.
Resp. Dis. 108: 1175-1184.
9. DeGiorgi, C. F., R. O. Fernandez, et al. (1996). "Ultraviolet-B lethal damage on
Pseudomonas aeruginosa." Current Microb. 33: 141-146.
10. El-Adhami, W., S. Daly, et al. (1994). "Biochemical studies on the lethal effects of
solar and artificial ultraviolet radiation on Staphylococcus aureus." Arch. Microbiol.
161: 82-87.
11. Fernandez, R. O. (1996). "Lethal effect induced in Pseudomonas aeruginosa
exposed to ultraviolet-A radiation." Photochem. & Photobiol. 64(2): 334-339.
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12. Fuerst, C. R. (1960). "Inactivation of bacterial viruses by physical means." Annals of
the New York Academy of Sciences 82: 684-691.
13. Futter, B. V. (1967). "Inactivation of bacterial spores by visible radiation." J. Appl.
Bact. 30(2): 347-353.
14. Gates, F. L. (1929). "A study of the bactericidal action of ultra violet light." J. Gen.
Physiol. 13: 231-260.
15. Glaze, W. H., G. R. Payton, et al. (1980). Oxidation of water supply refractory
species by ozone with ultraviolet radiation, U.S. EPA.
16. Goldstein, M. A. and N. M. Tauraso (1970). "Effect of formalin,B-propiolactone,
merthiolate, and ultraviolet light upon Influenza virus infectivity, chicken cell
agglutination, hemagglutination, and antigenicity." Appl. Microb. 19(2): 290-294.
17. Gurol, M. D. and R. Vatista (1987). "Oxidation of phenolic compounds by ozone and
ozone + UV radiation." Water Res. 21: 895.
18. Harstad, J. B., H.M.Decker, et al. (1954). "Use of ultraviolet irradiation in a room air
conditioner for removal of bacteria." American Industrial Hygiene Association
Journal 2: 148-151.
19. Hill, W. F., F. E. Hamblet, et al. (1970). "Ultraviolet devitalization of eight selected
enteric viruses in estuarine water." Appl. Microb. 19(5): 805-812.
20. Hollaender, A. (1943). "Effect of long ultraviolet and short visible radiation (3500 to
4900) on Escherichia coli." J. Bact. 46: 531-541.
21. Jagger, J. (1967). Ultraviolet Photobiology. Englewood Cliffs, Prentice-Hall, Inc.
22. Jensen, M. M. (1964). "Inactivation of airborne viruses by ultraviolet irradiation."
Applied Microbiology 12(5): 418-420.
23. Keller, L. C., T. L. Thompson, et al. (1982). "UV light-induced survival response in a
highly radiation-resistant isolate of the Moraxella-Acinetobacter group." Appl. &
Environ. Microb. 43(2): 424-429.
24. Knudson, G.B. (1986). "Photoreactivation of ultraviolet-irradiated, plasmid-bearing,
and plasmid-free strains of bacillus anthracis." Appl. & Environ. Microbiol. 52(3):
444-449.
25. Kundsin, R. B. (1966). "Characterization of Mycoplasma aerosols as to viability,
particle size, and lethality of ultraviolet radiation." J. Bacteriol. 91(3): 942-944.
26. Kundsin, R. B. (1968). "Aerosols of Mycoplasmas, L forms, and bacteria:
Comparison of particle size, viability, and lethality of ultraviolet radition." Applied
Microbiology 16(1): 143-146.
27. Lidwell, O. M. and E. J. Lowbury (1960). "The survival of bacteria in dust." Annual
Review of Microbiology 14: 38-43.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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28. Miller, W. R., E. T. Jarrett, et al. (1948). "Evaluation of ultraviolet radiation and dust
control measures in control of respiratory disease at a naval training center." 82: 86-
100.
29. Mitscherlich, E. and E. H. Marth (1984). Microbial Survival in the Environment.
Berlin, Springer-Verlag.
30. Mongold, J. (1992). "DNA repair and the evolution of transformation in Haemophilus
influenzae." Genetics 132: 893-898.
31. Morrissey, R. F. and G. B. Phillips (1993). Sterilization Technology. New York, Van
Nostrand Reinhold.
32. Munakata, N., M. Saito, et al. (1991). "Inactivation action spectra of Bacillus subtilis
spores in extended ultraviolet wavelengths (50-300 nm) obtained with synchrotron
radiation." Photochem. & Photobiol. 54(5): 761-768.
33. Philips (1985). Germicidal Lamps and Applications, Philips Lighting Div.
34. Phillips, G. B. and F. E. Novak (1955). "Applications of germicidal ultraviolet in
infectious disease laboratories." Appl. Microb. 4: 95-96.
35. Pollard, E. C. (1960). "Theory of the physical means of the inactivation of viruses."
Annals of the New York Academy of Sciences 82: 654-660.
36. Prengle, H. W. J. (1983). "Experimental rate constants and reactor conditions for the
destruction of micropollutants and trihalomethane precursors by ozone with
ultraviolet radiation." Environ. Sci. Technol. 17: 743.
37. Qualls, R. G. and J. D. Johnson (1983). "Bioassay and dose measurement in UV
disinfection." Appl. Microb. 45(3): 872-877.
38. Qualls, R. G. and J. D. Johnson (1985). "Modeling and efficiency of ultraviolet
disinfection systems." Water Res. 19(8): 1039-1046.
39. Rainbow, A. J. and S. Mak (1973). "DNA damage and biological function of human
adenovirus after U.V. irradiation." Int. J. Radiat. Bil. 24(1): 59-72.
40. Rauth, A. M. (1965). "The physical state of viral nucleic acid and the sensitivity of
viruses to ultraviolet light." Biophysical Journal 5: 257-273.
41. Rentschler, H. C., R. Nagy, et al. (1941). "Bactericidal effect of ultraviolet radiation."
J. Bacteriol. 42: 745-774.
42. Rentschler, H. C. and R. Nagy (1942). "Bactericidal action of ultraviolet radiation on
air-borne microorganisms." J. Bacteriol. 44: 85-94.
43. Riley, R. L. and F. O'Grady (1961). Airborne Infection. New York, The Macmillan
Company.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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44. Riley, R. L. K., J.E. (1972). "Effect of relative humidity on the inactivation of airborne
Serratia marcescens by ultraviolet radiation." Applied Microbiology 23(6): 1113-
1120.
45. Riley, R. L. and E. A. Nardell (1989). "Clearing the air: The theory and application of
ultraviolet disinfection." Am. Rev. Resp. Dis. 139: 1286-1294.
46. Scheir, R. and F. B. Fencl (1996). "Using UVC Technology to Enhance IAQ." HPAC
Feb.
47. Seagal-Maurer, S. and G. E. Kalkut (1994). "Environmental control of tuberculosis:
Continuing controversy." Clinical Infectious Diseases 19: 299-308.
48. Severin, B. F., M. T. Suidan, et al. (1983). "Kinetic modeling of U.V. disinfection of
water." Water Res. 17(11): 1669-1678.
49. Severin, B. F. (1986). "Ultraviolet disinfection for municipal wastewater." Chemical
Engineering Progress 81: 37-44.
50. Shama, G. (1992). "Inactivation of Escherichia coli by ultraviolet light and hydrogen
peroxide in a thin film contactor." Letters in Appl. Microb. 15: 259-260.
51. Shama, G. (1992). "Ultraviolet irradiation apparatus for disinfecting liquids of high
ultraviolet absorptivities." Letters in Appl. Microb. 15: 69-72.
52. Sharp, D. G. (1938). "A quantitative method of determining the lethal effect of
ultraviolet light on bacteria suspended in air." J. Bact. 35: 589-599.
53. Sharp, G. (1939). "The lethal action of short ultraviolet rays on several common
pathogenic bacteria." J. Bact. 37: 447-459.
54. Sharp, G. (1940). "The effects of ultraviolet light on bacteria suspended in air." J.
Bact. 38: 535-547.
55. Sylvania (1981). Sylvania Engineering Bulletin 0-342, Germicidal and Short-Wave
Ultraviolet Radiation, GTE Products Corp.
56. Takahashi, N. (1990). "Ozonation of several organic compounds having low
molecular weight under ultraviolet irradiation." Ozone Science & Engineering 12: 1-
17.
57. Tamm, I. and D. J. Fluke (1950). "The effect of monochromatic ultraviolet radiation
on the infectivity and hemagglutinating ability of the influenza virus type A strain PR-
8." J. Bact. 59: 449-461.
58. Taylor, A. R. (1960). "Effects of nonionizing radiations of animal viruses." Annals of
the New York Academy of Sciences 82: 670-683.
59. Von Sonntag, C. (1986). "Disinfection by free radicals and UV-radiation." Water
Supply 4: 11-18.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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60. Wang, Y. and A. Casadevall (1994). "Decreased susceptibility of melanized
Cryptococcus neoformans to UV light." Appl. Microb. 60(10): 3864-3866.
61. Wells, W. F. (1955). Airborne Contagion. New York, New York Academy of
Sciences.
62. Westinghouse (1982). Booklet A-8968, Westinghouse Electric Corp., Lamp Div.
63. Scheir, R. and F. B. Fencl ,Steril-Aire USA, Inc. (1997). Electric utility solves IAQ
problem with UVC electrical energy. (You'll want to know) HPAC Vol. 69, No. 5.
May, p28.
4.4 – OUTDOOR AIR PURGIN
OUTDOOR PURGE AIR SYSTEM
Airborne pathogens can be removed by purging with outside air, which is naturally
sterilized. Airborne bacteria and viruses pathogenic for humans rarely occur in the
outdoor air, and cannot survive long if they do. Spores of fungi and actinomycetes
can occur in outside air but rarely occur in hazardous concentrations (Goodfellow
1984). The concentration of fungal spores in outdoor air varies, but is often as low
as 100 CFU/m3 in residential areas (see Table 2.3).
The only condition in which purging with outside air is not a solution to an indoor
microbial contamination problem is when microbial growth has occurred inside the
air handling unit, because this may increase respiratory distress throughout the
building. Therefore, under normal conditions, purging a building with outside air is an
acceptable way of removing airborne pathogens, especially contagious human
pathogens.
Even the cleanest of human environments is full of microbes. Table 2.1 lists the
variety of airborne microorganisms that have been isolated on American and Soviet
spacecraft (Nicogossian 1977 & 1993, Johnson et al 1977). The last column
identifies those species that are found in outdoor air, based on several studies
(Kemp 1995, Li 1992, Straja 1996). This table highlights an important distinction --
contagious human pathogens are found concentrated indoors, not outdoors
(Gregory 1973), close to their main source, humans. Fungi can occur in both
locations (Samson 1994, Reponen 1992).
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Limits for Indoor Airborne Microbes
No standards exist for acceptable levels of indoor air contamination with
microorganisms, since the infectivity of pathogens is extremely species dependent,
although a number of guidelines exist for indoor spore levels, and a few exist for
indoor bacterial levels (Rao 1996, Su et al 1992, Godish 1995).
Table 2.3 and Table 2.4 summarize some of the lower levels that have been
suggested as limits, along with data from various sources indicating average
ambient outdoor or indoor levels. These limits are by no means the only limits
specified in the literature, but they are representative of the low end of all the limits
or averages that have been published. The bacteria referred to are implicitly
ambient, or environmental bacteria. Pathogenic bacteria and viruses, particularly
contagious pathogens, are considered to have no safe limits (Rao et al 1996).
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The rate of removal of airborne pathogens depends on two factors, the air change
rate (ACH) and the ventilation effectiveness (or degree of air mixing). If plug flow
(piston flow) were assumed, then one air change would completely remove all
pathogens that were initially present in a room. This is rarely the case, except when
it is by design (ASHRAE 1991).
Complete air mixing will delay the removal of airborne pathogens in an exponential
manner. This represents the limiting case for normal buildings, and is a reasonable
and simple model to use for evaluating the removal rate of airborne pathogens.
Given the assumption of complete air mixing, the primary factor determining the
removal of airborne pathogens is the air change rate.
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Airborne pathogen hazards are dependent on the species of microbe. Some
microbes are extremely lethal at very low doses. Some guidelines exist for levels of
airborne fungi, and these are used as general indicators. The ACGIH and the AIHA
define 1000 CFU/m3 as an upper limit for concentrations in indoor environments,
while the CEC defines 2000 CFU/m3 as a "very high" level (Rao et al 1996). A value
of 10,000 CFU/m3 of nondescript airborne microbes could therefore be considered a
hazardous level for indoor environments.
The chart below illustrates the purging effect of different rates of outdoor air, in
terms of ACH (air change per hour). The actual amount of outdoor air that can be
economically brought in to a building can depend heavily on ambient conditions. In
mild dry climates, large volumes of outdoor air can be used to purge a building
continuously with little added cost. In hot, dry climates it is possible to use two stage
evaporative coolers to recover a large fraction of exhaust cooling and thereby bring
in outdoor air at possible high volumes for a much reduced cost. In cold climates,
high efficiency air-to-air or run around heat exchangers can recover heat losses, but
the problem becomes one of economics as well as system operating parameters.
References
1. May, K. R., H.A.Druett, L.P.Packman (1969). “Toxicity of open air to a variety of
microorganisms.” Nature 221: 1146-1147.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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2. Cox, C. S., J.Baxter, B.J.Maidment (1973). “A mathematical expression for oxygen-
induced death in dehydrated bacteria.” Journal of General Microbiology 75: 179-
185.
3. Cox, C. S., F.Baldwin (1967). “The toxic effect of oxygen upon the aerosol survival
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4. de Jong, J. C., K.C.Winkler (1968). “The inactivation of poliovirus in aerosols.”
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5. Harper, G. J. (1961). “Airborne micro-organisms : survival tests with four viruses.”
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6. Benbough, J. E., A.M.Hood (1971). “Viricidal activity of open air.” Journal of Hygiene
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7. de Mik, G., I.de Groot (1977). “The germicidal effect of the open air in different parts
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8. Zeterberg, J. M. (1973). “A review of respiratory virology and the spread of virulent
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228-299.
9. Sullivan, J. F., J.R.Songer (1966). “Role of differential air pressure zones in the
control of aerosols in a large animal isolation facility.” Applied Microbiology 14(4):
674-678.
10. Lidwell, O. M. and R.E.O.Williams (1960). “The ventilation of operating-theatres.”
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Hygiene 58: 427-448.
12. Liu, R., and M.A.Huza (1995). “Filtration and indoor air quality: a practical
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13. Miller-Leiden, S., C. Lobascio and W.W.Nazaroff (1996). “Effectiveness of in-room
air filtration and dilution ventilation for tuberculosis infection control.” Journal of the
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14. ICCCS (1992). The Future Practice of Contamination Control. Proceedings of the
11th International Symposium on Contamination Control, Westminster, Mechanical
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15. Hers, J. F., K. C. Winkler, et al. (1973). Airborne Transmission and Airborne
Infection. VIth International Symposium on Aerobiology, Technical University at
Enschede, The Netherlands, Oosthoek Publishing Company.
16. Seagal-Maurer, S. and G. E. Kalkut (1994). “Environmental control of tuberculosis:
Continuing controversy.” Clinical Infectious Diseases 19: 299-308.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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17. Lidwell, O. M. (1960). “The evaluation of ventilation.” J. Hygiene 58: 297-305.
18. Brief, R. S. and T. Bernath (1988). “Indoor pollution: guidelines for prevention and
control of microbiological respiratory hazards associated with air conditioning and
ventilation systems.” Appl. Indust. Hyg. 3: 5-10.
19. ANSI (1992). American national standard for laboratory ventilation. New York,
American National Standards Institute.
20. Rivers, R. D. (1982). “Predicting particulate air quality in recirculatory ventilation
systems.” ASHRAE Transactions(82): 929949.
21. Clark, R. P. (1985). “Ventilation conditions and air-borne bacteria and particles in
operating theatres: proposed safe economies.” J. Hyg. 95: 325-335.
22. Hambraeus, A., S. Bengtsson, et al. (1977). “Bacterial contamination in a modern
operating suite.” J. Hyg. 79: 121-132.
23. Phelps, E. B., L. Buchbinder, et al. (1942). “Studies on Microorganisms in simulated
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341-358.
26. Jenkins, P. A. (1991). Mycobacteria in the environment. Pathogens in the
Environment. B. Austin. Oxford, Blackwell Scientific Publications.
27. Kowalski, W. J. (1997). Master's Thesis -- Technologies for controlling respiratory
disease transmission in indoor environments: Theoretical performance and
economics., Ann Arbor, UMI Dissertation Services.
28. Li, D.-W. and B. Kendrick (1995). “A year-round comaprison of fungal spores in
indoor and outdoor air.” Mycologia 87(2): 190-195.
29. Pasanen, A.-L. and e. al (1991). Airborne bacteria and fungi in rural houses in
Finland. IAQ '91. Washington, Healthy Buildings/IAQ '91.
30. Burge, H. (1990). “Bioaerosols: Prevalence and health effects in the indoor
environment.” J. Allerg. Clin. Immunol. 86(5): 687-781.
31. Fulton, J. D. and et al (1966). “Microorganisms of the upper atmosphere, I - V.”
Appl. Microbiol. 14(2): 232.
32. Pady, S. M. (1957). “Quantitative studies of fungus spores in the air.” Mycologia 49:
339-353.
33. Nardell, E. A., J. Keegan, et al. (1991). “Airborne infection: Theoretical limits of
protection acheivable by building ventilation.” Am. Rev. Resp. Dis. 144: 302-306.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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34. Tamblyn, R. T. (1995). “Toward zero complaints for office air conditioning.” Heating,
Piping & Air Conditioning March: 67-72.
4.5 - ELECTROSTATIC PRECIPITATION
Electrostatic
precipitators are
commonly used to
remove particles from
airstreams having large
steady flow rates.
Typical applications
include coal-burning
plants and cement kilns.
A typical two-stage
electrostatic precipitator
has a stage of corona
wires and a stage of collecting plates, as illustrated in the diagram at right. The
corona wires are maintained at several thousand volts which produces a corona that
releases electrons into the airstream. These electrons attach to dust particles and
give them a net negative charge. The collecting plates are grounded and attract the
charged dust particles. The collecting plates are periodically rapped by mechanical
rappers to dislodge the collected dust, which then drop into hoppers below. The air
velocity between the plates needs to be sufficiently low to allow the dust to fall and
not to be re-entrained in the airstream.
It takes between 0.01 and 0.1 second for dust particles to acquire a charge in the
corona region. Industrial systems are normally designed with more than 1 second
residence time in the first stage to assure the charging of dust particles. Industrial
systems are capable of removing particles in the size range 0.01 -- 10 microns and
can achieve efficiencies in the neighborhood of 95%.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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Small electrostatic precipitators designed for home or other non-industrial
applications are known as electronic air cleaners. These do not have rappers, but
must be taken apart and cleaned periodically. also, these devices are often inserted
into airstreams without regard to residence time or air velocities, and hence
efficiencies can be much lower than those used in industrial applications. A well-
designed electronic air cleaner for home or office building applications would not
only be relatively large and have a high energy demand, but it would also generate
ozone at potentially hazardous levels.
Even a well-sized, efficinently operating air cleaner cannot achieve the efficiency
necessary to guarantee complete interception of airborne bacteria, let alone viruses.
However, as a means of simply improving air quality and decreasing dust and
airborne microbes, electronic air cleaners do indeed have some value in homer and
office building environments.
No studies exist which examine the effectiveness of electrostatic precipitators in
controlling airborne microorganisms. A computer simulation is currently in progress
at Penn State which analyzes the effectiveness of electrostatic precipitation in
controlling airborne microbes in a model building. The results of this study will be
presented here upon completion.
References
1. Heinsohn, R.J., Kabel, R.L. (1996). Sources and Control of Air Pollution. The
Pennsylvania State University.
2. Khare, M. and M. S. (1996). "Computer aided simulation of efficiency of an
electrostatic precipitator." Environment International 22(4): 451-462.
3. Mohr, M., B.A.Kwetkus and H.Burtscher (1993). "Improvement of electrostatic
precipitation by UV-charging of submicron particles." Journal of Aerosol Science
24(S1): s247-s248.
4. Seto, K., K. Okuyama and Y. Inuoe (1995). "Electrostatic precipitation of fine
particulate contaminants by UV/photoelectron method under low pressure
condition." Journal of Aerosol Science 26(S1): s17-s18.
5. Stenhouse, J. I. T. and K. B. (1990). "Aerosol deposition in e;ectrostatic
precipitators." Journal of Aerosol Science 21(s1): s703-s706.
6. Zhibin, Z. and Z. G. (1992). "New model of electrostatic precipitation efficiency
accounting for turbulent mixing." Journal of Aerosol Science 23(2): 115-121.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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4.6 – NEGATIVE AIR IONIZATION
Negative air ionization has the potential to reduce the concentration of airborne
microorganisms. The effect appears to result from the ionization of bioaerosols and
dust particles that may carry microorganisms, causing them to settle out more
rapidly. Settling tends to occur on horizontal surfaces, especially metallic surfaces,
and generally in the area near the ionization unit. Ionization may enhance
agglomeration, creating larger particles out of smaller particles, thereby increasing
the settling rate. Ionization may also cause attraction between ionized particles and
grounded surfaces.
In situations where dust may carry microorganisms, negative air ionization can be
economical to use to reduce infections. It has been used economically to reduce the
incidence of Newcastle Disease Virus in poultry houses (Mitchell 1994). Poultry
houses can be notoriously dusty.
The above chart shows the Colony Forming Units (CFU) measured with and without
ionization in a dental clinic by Gabbay et al (1990). Airborne microbial levels were
reduced by 32-52% with ionization. He also found that horizontal plates picked up
considerably more cultures than vertical plates, strongly suggesting that settling out
of ionized particles was the primary mode of removal.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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This chart summarizes the results of studies by Makela et al (1979), who found that
bacterial aerosols in patient rooms of a burns and plastic surgery unit could be
reduced with air ionization. Variations in the bacterial levels were associated with
bed-changing and other room activities. The humidity in the rooms was low, which
may have enhanced the effect.
In this chart, also based on results from Makela et al (1979), specifically identified
Staphylococcus aureus levels in a room with and without ionization. The average for
two days of monitoring indicated a definitive reduction in airborne levels.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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Staphylococcus aureus is a potential nosocomial infectious agent of wounds and
burns.
The chart above summarizes some results from Happ et al (1966), who found that
levels of aerosolized virus T1 bacteriophage were rduced under various types of
ionization, which included mixed ions, negative ions and positive ions. All three
types of ionization had comparable results in terms of reducing airborne levels. The
method used by Happ involved testing the filtration efficiency, in which lower filter
efficiencies demonstrated lower recoveries rom the air. These lower recoveries
suggested either that the phage was not present in the air or had perhaps been
inactivated.
TYPICAL SPECIFICATIONS FOR ION GENERATORS
Ion Generation Method Pulse Ionization Field
Power Supply 9 kV - 15 kV
Wattage 0.75 - 2.7 W
Ozone Production < 0.02 PPM
References
1. Gabbay, J. (1990). “Effect of ionization on microbial air pollution in the dental clinic.”
Environ. Res. 52(1): 99.
2. Happ, J. W., J. B. Harstad, et al. (1966). “Effect of air ions on submicron T1
bacteriophage aerosols.” Appl. Microb. 14: 888-891.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
39
3. ICCCS (1992). The Future Practice of Contamination Control. Proceedings of the
11th International Symposium on Contamination Control, Westminster, Mechanical
Engineering Publications.
4. Mitchell, B. W. a. D. J. K. (1994). “Effect of negative air ionization on airborne
transmission of newcastle disease virus.” Avian Diseases 38: 725-732.
5. Mitchell, B. W. (1994). “Effect of negative air ionization on airborne transmission of
Newcastle Disease Virus.” Avian Dis. 38(4): 725.
6. Phillips, G., G. J. Harris, et al. (1963). “The effect of ions on microorganisms.” Int. J.
Biometerol. 8: 27-37.
7. Estola, T., P. Makela, et al. (1979). "The effect of air ionization on the air-borne
transmission of experimental Newcastle disease virus infections in chickens." J.
Hyg. 83: 59-67.
8. Kreuger, A. P., R. F. Smith, et al. (1957). "The action of air ions on bacteria." J. Gen.
Physiol. 41: 359-381.
9. Krueger, A. P. and E. J. Reed (1976). "Biological Impact of Small Air Ions." Science
193(Sep): 1209-1213.
10. Lehtimaki, M. and G. Graeffe (1976). The effect of the ionization of air on aerosols
in closed spaces. Proceedings of the 3rd International Symposium on
Contamination Control, Copenhagen.
11. Makela, P., J. Ojajarvi, et al. (1979). "Studies on the effects of ionization on bacterial
aerosols in a burns and plastic surgery unit." J. Hyg. 83: 199-206.
12. Phillips, G., G. J. Harris, et al. (1964). "Effect of air ions on bacterial aerosols." Intl.
J. of Biometerol. 8: 27-37.
13. Soyka, F. & A. Edmonds (1991). "The Ion Effect" Bantam Books.
(Many thanks to the people at Electrocorp for providing some of the above
information and support for the ongoing studies of negative air ionization at PSU.)
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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4.7 – VEGETATION
VEGETATION AND AIR DESINFECTATION
A handful of studies have investigated the use of vegetation as a means of removing
or reducing levels of airborne microorganisms. This has sometimes been referred to
as "growing clean air." Recently a Canadian firm developed what it called a
"breathing wall," or a wall of plants and waterfalls that seems to improve air quality
(ASHRAE Journal 1998, May, p58). Earlier results of studies by government
agencies seemed inconclusive but recent experience suggests there may be merit
to this idea.
The reasons that vegetation may reduce levels of airborne microorganisms are
varied. The surface area of large amounts of vegetation may absorb or adsorb
microbes or dust. The oxygen generation of the plants may have an oxidative effect
on microbes. The increased humidity may have an effect on reducing some
microbial species although it may favor others. The presence of symbiotic microbes
such as streptomyces may cause some disinfection of the air. Natural plant
defences against bacteria may operate against mammalian pathogens.
One downside to keeping large amounts of vegetation indoors is that the potting soil
may include potentially allergenic fungi. The presence of moisture may also
contribute to fungal problem. Clearly there is some balance to be achieved between
the desirable and undesirable effects.
The use of waterfalls in conjunction with vegetation will increase local humidity.
Humidity has mixed effects, as stated before, but the use of moving water may
generate positive or negative ions, or may simply cause hygrophobic microbes to
precipitate out of the air. The evaporative cooling effect of dripping water may chill
some microbes into inactivation. Cooling coils have a similar effect. Evaporative
coolers (not warm cooling towers) may have a similar effect.
A possible application might be to route building return air through a greenhouse.
Not only will some filtering effects occur, but oxygen will be replenished and the
solar exposure will cause some air disinfection.
Few references are available at present, but those that provide related information
are listed below.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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References
1. Burroughs, H. E. B. (1997). “IAQ: An environmental factor in the indoor habitat.”
HPAC, 69(2), 57-60.
2. Cox, C. S., F.Baldwin. (1967). “The toxic effect of oxygen upon the aerosol survival
of Escherichia coli.” Journal of General Microbiology, 49, 115-117.
3. Davey, B., and Halliday, T. (1994). Human biology and health: An evolutionary
approach, Open University Press, London.
4. de Jong, J. C., K.C.Winkler. (1968). “The inactivation of poliovirus in aerosols.”
Journal of Hygiene, 66, 557-565.
5. de Mik, G., I.de Groot. (1977). “The germicidal effect of the open air in different
parts of the Netherlands.” J. Hygiene, 78, 175-187.
6. Dorgan, C. B., Dorgan, C. E., Kanarek, M. S., and Willman, A. J. (1998). “Health
and productivity benefits of improved air quality.” ASHRAE Transactions, 104(1).
7. Estola, T., Makela, P., and Hovi, T. (1979). “The effect of air ionization on the air-
borne transmission of experimental Newcastle disease virus infections in chickens.”
J. Hyg., 83, 59-67.
8. Fisk, W. (1994). “The California healthy buildings study.” Center for Building
Science News, Spring 1994, 7,13.
9. Fisk, W., and Rosenfeld, A. (1997). “Improved productivity and health from better
indoor environments.” Center for Building Science News, Summer, 5.
10. Futter, B. V. (1967). “Inactivation of bacterial spores by visible radiation.” J. Appl.
Bact., 30(2), 347-353.
11. Gregory, P. H. (1973). Microbiology of the atmosphere, Leonard Hill Books,
Plymouth.
12. Harper, G. J. (1961). “Airborne micro-organisms : survival tests with four viruses.”
Journal of Hygiene, 59, 479-486.
13. Hatch, M. T., and Dimmick, R. L. (1966). “Physiological responses of airborne
bacteria to shifts in relative humidity.” Bacteriological Reviews, 30(3), 597.
14. Hautanen, J., T.Watanabe, T.Tuschida, Y.Koizumi, F.Tochikubo, E.Kauppinen,
K.Lehtinen and J.Jokiniemi. (1995). “Brownian agglomeration of bipolarly charged
aerosol particles.” Journal of Aerosol Science, 26(S1), s21-s22.
15. Hyvarinen, A., O'Rourke, M. K., Meldrum, J., Stetzenbach, L., and Reid, H. (1995).
“Influence of cooling type on airborne viable fungi.” Journal of Aerosol Science,
26(S1), s887-s888.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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16. Isaac, S. (1996). “To what extent do airborne fungal spores contribute to respiratory
disease and allergic reactions in humans?” Mycologist, 10(1), 31-32.
17. Kreuger, A. P., Smith, R. F., and Go, I. G. (1957). “The action of air ions on
bacteria.” J. Gen. Physiol., 41, 359-381.
18. Krueger, A. P., and Reed, E. J. (1976). “Biological Impact of Small Air Ions.”
Science, 193(Sep), 1209-1213.
19. Lidwell, O. M., and Lowbury, E. J. (1960). “The survival of bacteria in dust.” Annual
Review of Microbiology, 14, 38-43.
20. May, K. R., H.A.Druett, L.P.Packman. (1969). “Toxicity of open air to a variety of
microorganisms.” Nature, 221, 1146-1147.
21. Phelps, E. B., Buchbinder, L., and Solowey, M. (1942). “Studies on Microorganisms
in simulated room environments, I, II, III.” J. Bacteriol., 42, 321-366.
22. Phillips, G., Harris, G. J., and Jones, M. V. (1964). “Effect of air ions on bacterial
aerosols.” Intl. J. of Biometerol., 8, 27-37.
23. Puckorius, P. R., Thomas, P. T., and Augspurger, R. L. (1995). “Why evaporative
coolers have not caused Legionnaire's Disease.” ASHRAE Journal, Jan, 29-33.
24. Stroh, G., and Stahl, W. “Effect of surfactants on the filtration properties of fine
particles.” Filtech 89, Karlesruhe, West Germany.
25. Watanabe, T., F.Tochikubo, J.Hautanen and E.I.Kauppinen. (1995). “Review of
particle agglomeration.” Journal of Aerosol Science, 26(S1), s19-s20.
26. Wise, J. A. (1997). “How nature nurtures: Buildings as habitats and their benefits to
people.” HPAC, 69(2), 48.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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5. - DESCRIPTON OF DEVELOPMENTAL AIRBONE PATHOGEN CONTROL
TECHNOLOGIES
5.1 – PHOTOCATALYTIC OXIDATION
PHOTOCATALYTIC OXIDATION (PCO)
Titanium dioxide (TiO2) is a semiconductor photocatalyst with a band gap energy of
3.2 eV. When this material is irradiated with photons of less than 385 nm, the band
gap energy is exceeded and an electron is promoted from the valence band to the
conduction band. The resultant electron-hole pair has a lifetime in the space-charge
region that enables its participation in chemical reactions. The most widely
postulated reactions are shown here.
OH- + h+ _________> .OH
O2 + e- _________> O2-
Hydroxyl radicals and super-oxide ions are highly reactive species that will oxidize
volatile organic compounds (VOCs) adsorbed on the catalyst surface. They will also
kill and decompose adsorbed bioaerosols. The process is referred to as
heterogeneous photocatalysis or, more specifically, photocatalytic oxidation (PCO).
Several attributes of PCO make it a strong candidate for indoor air quality (IAQ)
applications. Pollutants, particularly VOCs, are preferentially adsorbed on the
surface and oxidized to (primarily) carbon dioxide (CO2). Thus, rather than simply
changing the phase and concentrating the contaminant, the absolute toxicity of the
treated air stream is reduced, allowing the photocatalytic reactor to operate as a
self-cleaning filter relative to organic material on the catalyst surface.
Photocatalytic reactors may be integrated into new and existing heating, ventilation,
and air conditioning (HVAC) systems due to their modular design, room temperature
operation, and negligible pressure drop. PCO reactors also feature low power
consumption, potentially long service life, and low maintenance requirements. These
attributes contribute to the potential of PCO technology to be an effective process
for removing and destroying low level pollutants in indoor air, including bacteria,
viruses and fungi.
Technical issues that must be confronted before PCO reactors can be used in this
application include the formation of products of incomplete oxidation, reaction rate
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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inhibition due to humidity, mass transport issues associated with high-flow rate
systems, catalyst deactivation and inorganic contamination (dust and soil).
(The above information was provided courtesy of Dr. Bill Jacoby)
References
1. Block, S. S.; Goswami, D.Y. (1995). "Chemically enhanced sunlight for killing
bacteria." Solar Engineering - ASME 1995 1: 431-437.
2. Goswami, D. Y.; Trivedi, D.M.; Block, S.S. (1995). "Photocatalytic disinfection of
indoor air." Solar Engineering - ASME 1995 1: 421-427.
3. Ireland, J. C. K., P.; Rice, E.W.; Clark, R.M. (1993). "Inactivation of Escherichia coli
by titanium dioxide photocatalytic oxidation." Applied and Environmental
Microbiology 59(5): 1668-1670.
4. Jacoby, W. A.; Blake, D.M.; Fennell, J.A.; Boulter, J.E.; Vargo, L.M. (1996).
"Heterogeneous photocatalysis for control of volatile organic compounds in indoor
air." Journal of Air & Waste Management 46: 891-898.
5. Matusunga, T. (1985). "Sterilization with particulate photosemiconductor." Journal of
Antibacterial Antifungal Agents 13: 211-220.
6. Nagame, S.; Oku, T. Kambara, M.; Konishi, K. (1989). "Antibacterial effect of the
powdered semiconductor TiO2 on the viability of oral microorganism." Journal of
Dental Research 68: 1696-1697.
7. Saito, T.; Iwase, T.; Horie, J.; Morioka,T. (1992). "Mode of photocatalytic
bactericidal action of powdered semiconductor TiO2 on Streptococci mutans."
Journal of Photochemical Photobiology 14: 369-379.
5.2 – AIR OZONIZATION
OZONIZATION AND RECLAMATION
In this depicted system, ozone is injected into the airsteam and mixed in the turbulator
to a degree that would guarantee ozonization of all organic compounds, including viral
nucleic acids and bacteria. Due to the corrosiveness of the ozone, an efficient
reclamation system must be developed. Reclaimed ozone could be recycled to the
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
45
injector, or else neutralized and used to regenerate electricity which would feed back to
the regenerator.
An alternative to regeneration of the ozone is ozone filtration through the use of the
polymer NoXon, which removes ozone from air. This polymer, developed by Hoechst,
converts the ozone to oxygen. Reportedly, the triatomic ozone molecule is disrupted,
one of its oxygen atoms binds to the polymer, and the remaining two atoms form
diatomic oxygen. The polymer's active absorption sites eventually become saturated
and it must be regenerated or replaced. Although this product is not yet on the market,
its application to the above described system holds great potential.
Ozonization has proven extremely effective in water systems, but as yet no airside
systems have been developed and proven safe and effective. Ongoing research at
Penn State has found airborne concentrations of ozone highly effective at disinfecting
surfaces. The levels of ozone capable of producing rapid sterilization appear low
enough that natural decay, or decay enhanced by uv radiation, may be sufficient to
render the sterilized air breathable without recourse to ozone filtration. Results of this
research cannot be presented here at present, but summaries will be provided later, or
on request to interested parties.
References
1. Beltran, F. J. (1995). "Theoretical aspects of the kinetics of competitive ozone
reactions in water." Ozone Science and Engineering 17: 163-181.
2. Beltran, F. J. and P. Alvarez (1996). "Rate constant determination of ozone-
organic fast reactions in water using an agitated cell." Journal of Environmental
Science & Health A31(5): 1159-1178.
3. Botzenhart, K., G. M. Tarcson, et al. (1993). "Inactivation of bacteria and
coliphages by ozone and chlorine dioxide in a continuous flow reactor." Water
Science Technology 27(3-4): 363-370.
4. Broadwater, W. T., R. C. Hoehn, et al. (1973). "Sensitivity of three selected
bacterial species to ozone." Applied Microbiology 26(3): 393-393.
5. Bunning, G. and D. C. Hempel (1996). "Vital-fluorochromization oF
microorganisms using 3',6'-diacetylfluorescein to determine damages of cell
membranes and loss of metabolic activity by ozonation." Ozone Science and
Engineering 18: 173-181.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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6. Chang, C. Y., C. Y. Chiu, et al. (1996). "Combined self-absorption and self-
decomposition of ozone in aqueous solutions with interfacial resistance." Ozone
Science & Engineering 18: 183-194.
7. de Mik, G., I.de Groot (1977). "The germicidal effect of the open air in different
parts of the Netherlands." Journal of Hygiene 78: 175-187.
8. Elford, W. J. and J. v. d. Eude (1942). "An investigation of the merits of ozone
as an aerial disinfectant." Journal of Hygiene 42: 240-265.
9. Fetner, R. H. and R. S. Ingols (1956). "A comparison of the bactericidal activity
of ozone and chlorine against Escherichia coli at 1 C." Journal of General
Microbiology 15: 381-385.
10. Finch, G. R., D. W. Smith, et al. (1988). "Dose-response of Escherichia coli in
ozone demand-free phosphate buffer." Water Resources Technology 22(12):
1563-1570.
11. Finch, G. R. and D. W. Smith (1989). "Evaluation of empirical process design
relationships for ozone disinfection of water and wastewater." Ozone Science
and Engineering 12(2): 157-175.
12. Hall, R. M. and M. D. Sobsey (1993). "Inactivation of Hepatitis A virus and MS2
by ozone and ozone-hydrogen peroxide in buffered water." Water Science
Technology 27(3-4): 371-378.
13. Harakeh, M. S. and M. Butler (1985). "Factors influencing the ozone inactivation
of enteric viruses in effluent." Ozone Science & Engineering 6: 235-243.
14. Hart, J., I. Walker, et al. (1995). "The use of high concentration ozone for water
treatment." Ozone Science & Engineering 17: 485-497.
15. Hartman (1925). J. Am. Soc. Heat. & Vent. Engrs. 31: 33.
16. Heindel, T. H., R. Streib, et al. (1993). "Effect of ozone on airborne
microorganisms." Zbl. Hygiene 194: 464-480.
17. Katzenelson, E. and H. I. Shuval (1973). Studies on the disinfection of water by
ozone : viruses and bacteria. First International Symposium on Ozone for Water
& Wastewater Treament, Washington D.C., Hampson Press.
18. Katzenelson, E., G. Koerner, et al. (1979). "Measurement of the inactivation
kinetics of poliovirus by ozone in a fast-flow mixer." Applied and Environmental
Microbiology 37(4): 715-718.
19. Levenspiel, O. Chemical Reaction Engineering. New York, John Wiley & Sons.
20. Lockowitz, T. G., H. N. Guttman, et al. (1973). Deactivation of virus by
ozonation in a stirred tank reactor. First International Symposium on Ozone for
Water & Wastewater Treament, Washington D.C., Hampson Press.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
47
21. Masaoka, T., Y. Kubota, et al. (1982). "Ozone decontamination of bioclean
rooms." Applied and Environmental Microbiology 43(3): 509-513.
22. McCarthy, J. J. and C. H. Smith (1974). "A review of ozone and its application
to domestic wastewater treaTment." Journal of the American Water Works
Association 74: 718-729.
23. Mik, G. d. and I. d. Groot (1977). "Mechanisms of inactivation of bacteriophage
pX174 and its DNA in aerosols by ozone and ozonized cyclohexene." J.
Hygiene 78: 199-211.
24. Perez-Rey, R., H. Chavez, et al. (1995). "Ozone inactivation of biologically-risky
wastewaters." Ozone Science & Engineering 17: 499-509.
25. Rahn, O. (1945). "Death of bacteria by chemical agents." Biodynamica 5(96): 1-
14.
26. Reiger, I. H., G. Feucht, et al. (1995). "Selective adsorption of noxon for the
detection of ozone." Odours & VOC's Journal(December): 39-44.
27. Rice, R. G. (1997). "Applications of ozone for industrial wastewater treatment --
A review." Ozone Science & Engineering 18: 477-515.
28. Roy, D. (1981). "Mechanism of enteroviral inactivation by ozone." Applied and
Environmental Microbiology 41(3): 718-723.
29. Roy, D., R. S. Englebrecht, et al. (1982). "Comparative inactivation of six
enteroviruses by ozone." Journal of the American Water Works Association 74:
660-664.
30. Scott, D. B. M. and E. C. Lesher (1962). "Effect of ozone on survival and
permeability of Escherichia coli." Journal of Bacteriology 85: 567-576.
31. Sobsey, M. D. (1989). "Inactivation of health-related microorganisms in water by
disinfection processes." Water Science Technology 21(3): 179-195.
32. Sproul, O. J. and S. B. Majumdar (1973). Poliovirus inactivation with ozone in
water. First International Symposium on Ozone for Water & Wastewater
Treament, Washington D.C., Hampson Press.
33. Technology, N. I. S. t. (1992). "Photoinitiated ozone-water reaction." Journal of
Research of the National Institute of Standards and Technology 97(4): 499.
34. Vaughn, J. M., Y. S. Chen, et al. (1987). "Inactivation of human and simian
rotaviruses by ozone." Applied and Environmental Microbiology 53(9): 2218-
2221.
35. Zeterberg, J. M. (1973). "A review of respiratory virology and the spread of
virulent and possibly antigenic viruses via air conditioning systems." Annals of
Allergy 31: 228-299.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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5.3 –CARBON ADSORTION
Carbon adsorption is used primarily for removal of gases and vapors. It is
effective against volatile organic compounds (VOCs) but is not used for
control of airborne dust or microorganisms. It is, in fact, not advisable to use
carbon adsorption where particulate matter is present and may clog the
adsorbent bed.
Carbon adsorption depends on the use of materials like activated charcoal
which possess an enormous amount of surface area per unit mass. The
presence of this surface area allows gas molecules to adhere to the surface.
Though carbon adsorbers are unlikely to have a significant effect on airborne
microbes, they can be effective at removing VOCs generated by fungi and
bacteria, and so decrease the health threats.
Although it is not used for intercepting particulate matter, the use of carbon
adsorption for the control of airborne viruses, which are not much larger than
VOCs, is a potential application which remains to be studied. A mere tenfold
increase in pore size might be sufficient to adsorb viruses.
References
1. Heinsohn, R.J., Kabel, R.L. (1996). Sources and Control of Air Pollution. The
Pennsylvania State University.
2. Tamai, H. 1996. Synthesis of extremely large mesoporous activated carbon
and its unique adsorption for giant molecules. Chemistry of Materials. v8 n2
p454.
3. Delanghe, B. 1996. Removal of organic micropollutants by adsorption onto
fibrous activated carbon. Water Supply v14 n2 p177.
4. Gomez, A.F. 1995. Adsorption of Botulinum Toxin to activated charcoal with
a mouse bioassay. Annals of Emergency Medicine 25:818.
5. VanOsdell, D.W., L.E.Sparks. (1995). Carbon Adsorption for Indoor Air
Cleaning. ASHRAE Journal, February 1995. p34-40.
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6. Stenzel, M.H. 1993. Remove organics by activated carbon adsorption.
Chemical Engineering Progress. v89 n4 p36.
7. Liu, R.T. 1990. Removal of volatile organic compounds in IAQ concentrations
with short carbon bed depths. Proceedings of Indoor Air 90. Toronto,
Canada. p177-182.
5.4 – PASSIVE SOLAR EXPOSURE
Passive exposure to solar
irradiation as a means of
destroying airborne pathogens is
being investigated by the Penn
State Architectural Engineering
Department. The principle is that
ultraviolet, and other, radiation
from the sun is sufficient to sterilize most pathogens within the space of about 30-60
seconds. This is the primary reason most infectious microorganisms die in the
outdoor air. In the diagram shown at the right, the spectrum of light produced by the
sun is illustrated. The ultraviolet component of sunlight includes the range of 2050 -
3020 Angstroms, which is biocidal to microorganisms. UVGI systems operate at
2537 Angstroms, and can be highly effective.
In the design for a ten-story office building
shown at left, a portion of the windows
serves as the outside face of the duct, and
the rest of the duct can be inexpensive
plexiglas. The vertical red bars represent
very long runs of transparent ductwork, or
the Passive Solar Exposure (PSE) plenum.
These faces can be oriented east and west,
and as the air is mixed on the roof, the
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same sterilizing effect can be had moring or afternoon. Air exhausted from each
room passes into the PSE plenum and travels down to the first floor before turning
back up towards the roof. The air handling unit on the roof then filters (and
processes) the air for return, also through the PSE plenum.
In the alternate design depicted below the entire window area of each face serves
as a return or supply air plenum. As it is transparent on both sides the view is
preserved for the occupants. As in the design above, the air is reheated, or cooled,
and mixed at the zone itself. The red rectangles penetrating the window space each
represent a zone inlet and zone
exhaust. Except for the local zone
equipment, this building has no
ductwork at all.
The fact that the duct occupies
window space means there is no
additional cooling or heating load on
the building as the result of this
design. One innovation incorporated
in this design is the intake of outside
air at the individual room, where it is
mixed with return air in a ceiling
plenum. In addition, the return air is
heated (reheated) in the ceiling
plenum prior to mixing with the
outside air, which has improved
germicidal effects.
Cooling is accomplished with chilled water coils in the plenum and chilled
water is supplied from basement chillers.
The main advantage of this design is that the increased cost of operating this
system is very small, and also, the first cost of construction can be integrated
into the building design at a minor add-on cost.
One potential enhancement to this design is the incorporation of titanium
oxide PCO (Photocatalytic Oxidation) units into the PSE plenum. The
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ultraviolet light from the sun would activate the titanium dioxide and oxidize
any microorganisms in the plenum air. The effectiveness of such a design is
currently being explored at Penn State with a computer simulation of the ten
story building depicted in the wire frame drawing above. Other
enhancements and innovations are being investigated and will be presented
here upon project completion. For more information see the section on
Photocatalytic Oxidation.
References
1. Baseler, M. W., B.Fogelmark, R.Burrell (1983). "Differential toxicity of inhaled
gram-negative bacteria." Infection and Immunity 40(1): 133-138.
2. Beebe, J. M. (1958). "Stability of disseminated aerosols of Pastuerella
tularensis subjected to simulated solar radiations at various humidities."
Journal of Bacteriology 78: 18-24.
3. Benbough, J. E., A.M.Hood (1971). "Viricidal activity of open air." Journal of
Hygiene 69: 619-626.
4. Buckland, F. E., D.A.J.Tyrrell (1962). "Loss of infectivity on drying various
viruses." Nature 195: 1063-1064.
5. Cox, C. S., F.Baldwin (1967). "The toxic effect of oxygen upon the aerosol
survival of Escherichia coli." Journal of General Microbiology 49: 115-117.
6. Cox, C. S., J.Baxter, B.J.Maidment (1973). "A mathematical expression for
oxygen-induced death in dehydrated bacteria." Journal of General
Microbiology 75: 179-185.
7. de Jong, J. C., K.C.Winkler (1968). "The inactivation of poliovirus in
aerosols." Journal of Hygiene 66: 557-565.
8. de Mik, G., I.de Groot (1977). "The germicidal effect of the open air in
different parts of the Netherlands." Journal of Hygiene 78: 175-187.
9. Dimmock, N. (1967). "Differences between the thermal inactivation of
Picornaviruses at high and low temperatures." Virology 31: 338-353.
10. DOE (1994). BLAST : Building Loads Analysis and System
Thermodynamics, Department of Energy.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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11. Goodlow, R. G., F.A.Leonard (1961). "Viability and infectivity of
microorganisms in experimental airborne infection." Bacteriology Reviews
25: 182-187.
12. Harper, G. J. (1961). "Airborne micro-organisms : survival tests with four
viruses." Journal of Hygiene 59: 479-486.
13. Hemmes, J. H., K.C.Winkler, S.M.Kool (1960). "Virus survival as a seasonal
factor in Influenza and Poliomyelitis." Nature 188: 430-431.
14. Jensen, M. M. (1964). "Inactivation of airborne viruses by ultraviolet
irradiation." Applied Microbiology 12(5): 418-420.
15. Langmuir, A. D. (1961). "Epidemiology of airborne infection." Bacteriology
Reviews 25: 173-181.
16. May, K. R., H.A.Druett, L.P.Packman (1969). "Toxicity of open air to a
avariety of microorganisms." Nature 221: 1146-1147.
17. Sullivan, J. F., J.R.Songer (1966). "Role of differential air pressure zones in
the control of aerosols in a large animal isolation facility." Applied
Microbiology 14(4): 674-678.
18. Walton, G., J. Axley, J. Grot (1995). CONTAM95 : Contaminant Analysis
Program, NIST.
19. Wilkinson, T. R. (1966). "Survival of bacteria on metal surfaces." Applied
Microbiology 14: 303-307.
20. Zeterberg, J. M. (1973). "A review of respiratory virology and the spread of
virulent and possibly antigenic viruses via air conditioning systems." Annals
of Allergy 31: 228-299.
5.5 – PULSED LIGHT
PULSED LIGHT & PEF
Pulsed White Light (PWL), also called Pulsed Light or Pulsed UV Light,
involves the pulsing of a high-power xenon lamp for about 0.1-3 milliseconds
per some sources (Dunn 1990, Rowan 1999, Johnson 1982), or about 100
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microseconds to 10 milliseconds per other sources (Wekhof 2000). The
spectrum of light produced resembles the spectrum of sunlight but is
momentarily 20,000 times as intense (Bushnell et al. 1997). Figure 1
compares the spectrum of a single pulse of PWL with that of continuous
sunlight at the earth's surface, however, since only broad spectrum UV light
between 200-400 nm contributes to the disinfection effect, the comparison of
solar and PWL spectra has only illustrative value. The spectrum of PWL
includes a large component of ultraviolet light.
These high intensity flashes of broad spectrum white light pulsed several
times a second can inactivate microbes with remarkable rapidity and
effectiveness. The germicidal effect appears to be due to both the high
ultraviolet content and the brief heating effects (Wekhof 2000), however,
these systems can be tuned to produce pulsed light with different
compositions. The Figure below compares two different pulses in which the
frequency spectra have been shifted (Wekhof 2000). The brevity of the pulse
assures no heating effects will occur on a macroscopic level.
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Figure 2. (above) Spectra of a xenon flash lamp: 1- at a high current density
of 6.500 kA/cm2, 2- at a low current density of approx. 1000 kA/cm2.
This technology is currently being applied in the pharmaceutical packaging
industry where translucent aseptically manufactured bottles and containers
are sterilized in a once-through light treatment chamber. The chamber
generates a light intensity at the surface of the exposed containers of about
1.7 J/sq.cm., or 1.7 x E06 microWatt-s/sq.cm. Sunlight produces about 1359
Watts/sq.cm.
Only two or three pulses are sufficient to completely eradicate bacteria and
fungal spores. Two pulses at 0.75 J/cm2 each were sufficient to sterilize plate
cultures of Staphylococcus aureus from more than 7 logs of CFU (Dunn et al.
1997). Spores of Bacillus subtilis, Bacillus pumilus, Bacillus
stearothermophilus, and Aspergillus niger were inactivated completely from
6-8 logs of CFU with 1-3 pulses (Bushnell et al. 1998). These results are
depicted in Figure 3. One of the surprising aspects of PWL exposed cultures
is that they exhibit no tailing to their survival curves (Dunn et al. 1997). In
other words, there seems to be no innate capacity for resistance among
segments of the microbial populations, unlike other inactivation mechanisms.
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The exact mechanism by which PWL kills bacteria and spores appears to be
due to the effects of UV combined with a new disinfection mechanism --
disintegration of the cell wall (Wekhof 2000). While UV causes damage to the
nucleic acid and other components of the cell, the instantaneous heating of
the cell results in the rupture of the cell wall, or lysing. This disintegrating
effect has been demonstrated to occur in the absence of UV (Wekhof 2000,
Dunn 2000).
A comparison of the disinfection rates due to PWL with the disinfection rates
under UVGI exposure suggests that doses for sterilization by PWL are an
order of magnitude lower than that for UV exposure (Wekhof 1991, Rowan et
al 1999, Dunn 2000). Bacillus subtilis, for example is sterilized (99.999%
disinfection) by about 42,600 microW-s/cm2 of UV while requiring a dose of
only 4500 microW-s/cm2 under pulsed light. PWL clearly results in an
apparent synergy of the pulsed energy quanta as compared to the relatively
continuous stream of lower density UVGI quanta.
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In terms of the dose for sterilization, PWL may represent the most efficient
energy delivery mechanism to date. However, the generation of the pulse
requires a considerable amount of energy, and some units requires external
cooling. The power consumption for a typical pulsed light system is about
1000 W while similar results can be achieved with a UVGI system drawing
only 10 W of total power. Applications are therefore limited to situations
where the benefits of rapid sterilization outweigh the costs of pulse
generation, as in the pharmaceuticals and health care industries.
Limited data on energy consumption is currently available for pulsed light
technology, but one production unit uses four 14-inch Xenon gas lamps
powered by a pulsing unit. An economics of use analysis for PWL in food
applications estimates a cost of 0.1-0.4 cents/sq.ft. of irradiated surface area
(Dunn et al. 1997).
This technology has also been applied to water systems, such as for the
eradication of Cryptosporidium, and systems are currently available for such
applications. Water may attenuate the effects to some degree, and PEF may
more suitable for this application as it suffers less attenuation.
PEF involves the pulsing of an electric fields of about 4-14 kV/cm through a
liquid medium. The result of this momentary field is a membrane potential
across the bacterial cell wall of more than 1.0 V, which is sufficient to lyse or
damage the cell irreparably. The inactivation of various microbes, including
Escherichia coli, Lactobacillus brevis, Pseudomonas fluorescens, Bacillus
cereus spores, and S. cerevisiae has been found to be dependent on field
strength and treatment times that are unique to each species. Since this
method has little effect on proteins, enzymes, or vitamins, it is perfectly suited
for food processing where the liquid medium may be anything from boullion
soup to milk.
PWL is a variation of pulsed electric field technology. Electric fields and light
are both electromagnetic radiation, however, the mechanism of inactivation
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due to electric fields appears to be distinctly different. In addition, spores do
not appear to be inactivated by pulsed electric fields.
PEF sterilization requires an electric fields of no less than 8 kV/cm. PEF
exposure exhibits the characteristic survival tail and conforms to the standard
logarithmic decay rate (death curve/survival curve) of microbes subjected to
lethal mechanisms such as radiation, biocides, and heating.
There are currently two manufacturers of pulsed light technologies,
PurePulse Technologies, Inc. of San Diego and Wek-Tec of Heilbronn,
Germany.
References
1. Bushnell, A., Clark, W., Dunn, J., and Salisbury, K. (1997). “Pulsed light
sterilization of products packaged by blow-fill-seal techniques.”
Pharmaceutical Engineering, 17(5), 74-84.
2. Bushnell, A., Cooper, J. R., Dunn, J., Leo, F., and May, R. (1998). “Pulsed
light sterilization tunnels and sterile-pass-throughs.” Pharmaceutical
Engineering, March/April, 48-58.
3. Clark, W., Bushnell, A., Dunn, J., and Ott, T. (1997). “Pulsed light and pulsed
electric fields for food preservation.” AIChE Annual Meeting Abstract.
4. Clark, W., A, B., Dunn, J., and Ott, T. “Pulsed Light and Pulsed Electric
Fields for Food Preservation, Paper 65f.” AIChE Annual Meeting.
5. Dunn, J., Burgess, D., and Leo, F. (1997). “Investigation of pulsed light for
terminal sterilization of WFI filled blow/fill/seal polyethylene containers.”
Parenteral Drug Association J. of Pharm. Sci. & Tech., 51(3), 111-115.
6. Dunn, J., Bushnell, A., Ott, T., and Clark, W. (1997). “Pulsed white light food
processing.” Cereal Foods World, 42(7), 510-515.
7. Grahl, T., and Markl, H. (1996). “Killing of microorganisms by pulsed electric
fields.” Applied Microbiology and Biotechnology, 45, 148-157.
8. Keith, W. D., Harris, L. J., Hudson, L., and Griffiths, M. W. (1997). “Pulsed
electric fields as a processing alternative for microbial reduction in spice.”
Food Research Intl., 30(3/4), 185-191.
COLLEGE OF ENGINEERING Deparatament of Architectural – Enginnering http://www.engr.psu.edu/iec/abe/topics.asp
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9. Peleg, M. (1995). “A model of microbial survival after exposure to pulsed
electric fields.” J. Sci. Food Agric., 67, 93-99.
10. Perkins, R. C., and Honig, W. M. (1991). “A high-intensity pulsed light source
in blue and UV from commercial fluorescent tubes.” IEEE Photonics
Technology Letters, 3(1), 91-92.
11. Qin, B., Zhang, Q., and Barbosa-Canovas, G. V. (1994). “Inactivation of
microorganisms by pulsed electric fields of different voltage waveforms.”
IEEE Transactions on Dielectrics and Electrical Insulation, 1(6), 1047-1056.
12. Qin, B., Pothakamury, U. R., Barbosa-Canovas, G. V., and Swanson, B. G.
(1996). “Nonthermal pasteurization of liquid foods using high-intensity pulsed
electric fields.” Critical reviews in Food Science and Nutrition, 36(6), 603-627.
13. Rice, J. (1994). “Sterilizing with light and electrical impulses.” Food
Processing, July, 66.
14. Schoenbach, K. H., Peterkin, F. E., Alden, R. W., and Beebe, S. J. (1997).
“The effect of pulsed electric fields on biological cells: Experiments and
applications.” IEEE Transactions on Plasma Science, 25(2).
15. Wouters, P. C., and Smelt, J. P. P. M. (1997). “Inactivation of
microorganisms with pulsed electric fields: Potential for food preservation.”
Food Biotechnology, 11(3), 193-229.
16. Zhang, Q., Qin, B., Barbosa-Canovas, G. V., and Swanson, B. G. (1995).
“Inactivation of E. coli for food pasteurization by high-strength pulsed electric
fields.” J. of Food Processing and Preservation, 19, 103-118.
17. Bruhn, R. E. (1997). “Electrical environment surrounding microbes exposed
to pulsed electric fields.” IEEE Transactions: Dielectrics & Electrical
Insulation, 4(6), 806.
18. Castro, A. J. (1993). “Microbial inactivation of foods by pulsed electric fields.”
J. of Food Processing and Preservation, 17(1), 47.
19. Dunn, J. (1995). “Pulsed-light treatment of food and packaging.” Food Tech.,
49(9), 95.
20. Dunn, J. (1997). “Investigation of pulsed light for terminal sterilization of WFI
filled blow/fill/polyethylene seal containers.” PDA J. of Pharm. Sci. & Tech.,
51(3), 111.
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21. Dunn, J. (2000). Private communication with W. J. Kowalski / unpublished
test results.
22. Martin, O. (1997). “Inactivation of Escherichia coli in skim milk by high
intensity pulsed electric fields.” J. of Food Process Eng., 20(4), 317.
23. Martin-Belloso, O. (1997). “Inactivation of Escherichi coli suspended in liquid
egg using pulsed electric fields.” J. of Food Processing and Preservation,
21(3), 193.
24. Pothakamury, U. R. (1996). “Effect of growth stage and processing
temperature on the inactivation of E. coli by pulsed electric fields.” J. of Food
Protection, 59(11), 1167.
25. Qin, B. (1994). “Inactivation of microorganisms by pulsed electric fields of
different voltage waveforms.” IEEE Transactions of Dielectric & Electrical
Insulation, 1(6), 1047.
26. Vega-Mercado, H. (1996). “Inactivation of Escherichia coli by combining pH,
ionic strength and pulsed electric fields.” Food Res. Intl., 29(2), 117.
27. Vega-Mercado, H. (1997). “Non-thermal food preservation: Pulsed electric
fields.” Trends in Food Science & Tech., 8(5), 151.
28. Wekhof, A. (1991). Environmental Progress, V. 10, n. 4, pp. 241 - 247,
U.S.A.,TREATMENT OF CONTAMINATED WATER, AIR AND SOIL WITH
UV FLASHLAMPS.
29. Wekhof, A. (1992). Hazardous Materials Control, V. 5, N. 6. pp. 48 -54,
U.S.A., with E.N. Folsom and Yu. Halpen: TREATMENT OF
GROUNDWATER WITH UV-FLASHLAMPS - THE THIRD GENERATION
OF UV SYSTEMS.
30. Wekhof, A. (1992). Rev. Sci. Instruments, V.. 63, n. 12, pp.5565 -5569 : A
LINEAR ULTRAVIOLET FLASHLAMP WITH SELF-REPLENISHING
CATHODE.
31. Wekhof, A. (1992) Patent N. 5,144,146: METHOD FOR DESTRUCTION OF
TOXIC SUBSTANCES WITH ULTRAVIOLET RADIATION.
32. Wekhof, A. (1992) Patent N. 5,124,131: COMPACT HIGH-THROUGHPUT
ULTRAVIOLET PROCESSING CHAMBER.
33. Wekhof, A. (1992). Patent N. 5,170,091: LINER ULTRAVIOLET
FLASHLAMP WITH SELF-REPLENISHING CATHODE.
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34. Wekhof, A. (2000). Pharma+Food, January, Hüttig Verlag Heidelberg
Germany.
35. Zhang, Q. (1994). “Inactivation of Saccharomyces cerevisiae in apple juice
by square-wave and exponential decay pulsed electric fields.” J. of Food
Process Eng., 17(4), 469.
5.6 – ULTRASONIC ATOMIZATION
Ultrasonics are capable of atomizing water droplets, and in theory could atomize
bacteria, which contain, or are contained in water. Viruses, which are either
contained within droplets of water or have organic components such as DNA, RNA
or proteins, should also be atomizable. There are two methods by which this may be
accomplished, supersonic nozzles and sonic generators.
If the airstream is forced through a supersonic nozzle, a standing shock wave
develops at the nozzle outlet. This shock wave dissipates energy by imparting it to
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the airstream, causing it to expand suddenly and rapidly. This results in the
atomization, or reduction to gas, of all bioaerosols in the airstream. The fan power or
pumping power required to accomplish this however, would be considerable.
The use of a sonic generator to create the standing shock wave has the advantage
of being much more efficient, as they are purely electronic. The sonic generator,
essentially a high-power speaker and amplifier, tuned to resonate within the
ductwork cavity, would create a standing shock wave through which the airstream
would pass, and in which atomization of any bioaerosols would occur. Both this and
the supersonic nozzle system would require a sound insulated ductwork section with
inlet and outlet silencers.
5.7 – MICROWAVE ATOMIZATION
This schematic diagram represents a simplified version of a microwave
sterilization system in which the airstream is sandwiched between the dielectric
surfaces. Alternatively, the airstream could be routed through a large microwave
cavity. The energy efficiency of the microwave system outlined above would likely
be unsurpassed, as essentially only the energy imparted to polar molecules in the
airstream would be converted.
Microwaves consist of mutually
perpendicular electrical waves and
magnetic waves, as depicted in the
diagram at the right. Each of these
components has an effect on the
water molecules and other organic molecules which make up the bacterial cell or
viral structure. The water molecules will rotate at or near the microwave frequency,
and this energy translates into linear motion. Linear motion of gas or liquid defines
heat, and this thermal activity ultimately disrupts the cell and viral structures.
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Microwaves have been demonstrated to have biocidal effects due to the heating
they induce, and are used to sterilize equipment. Normally this requires extended
exposure times, but with a boost in power the exposure times could theoretically be
reduced. In addition, there exists a phenomenon called the microwave effect which
appears to destroy viruses for reasons other than heating.The system depicted
above would be optimized to take advantage of the Microwave Effect. For more
extensive information on microwaves and the microwave effect see the section titled
DNA and the Microwave Effect.
Of related interest is microwave induced resonance.The first three harmonic modes
of DNA have been shown to be excitable in the range of 2.5 - 20 Ghz by Davis et al.
A sufficient power level could disrupt the molecule altogether. Vibrational and
rotational resonance has been demonstrated at much lower frequencies by various
researchers for both RNA & DNA. The specific frequencies and power levels
necessary to dissociate virus nucleic acids remain to be determined
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PART 3 – PUBLICATONS
PUBLICATION DOWNLOAD
http://www.engr.psu.edu/iec/abe/publications.asp