aereobiological enginnering topics - pennsylvania

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

http://www.engr.psu.edu/iec/abe/database.asp#v

http://www.engr.psu.edu/iec/abe/database.asp#b

http://www.engr.psu.edu/iec/abe/database.asp#f

http://www.engr.psu.edu/iec/abe/database/pathogen_list.asp


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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

http://www.engr.psu.edu/iec/abe/control/isolation.asp

http://www.engr.psu.edu/iec/abe/control/filtration.asp

http://www.engr.psu.edu/iec/abe/control/ultraviolet.asp

http://www.engr.psu.edu/iec/abe/control/outdoor_purge.asp

http://www.engr.psu.edu/iec/abe/control/electrostatic.asp

http://www.engr.psu.edu/iec/abe/control/neg_ion.asp

http://www.engr.psu.edu/iec/abe/control/vegetation.asp

http://www.engr.psu.edu/iec/abe/control/photocatalytic.asp

http://www.engr.psu.edu/iec/abe/control/ozonization.asp

http://www.engr.psu.edu/iec/abe/control/carbon_adsorption.asp

http://www.engr.psu.edu/iec/abe/control/passive_solar.asp

http://www.engr.psu.edu/iec/abe/control/ultrasonic.asp

http://www.engr.psu.edu/iec/abe/control/microwave.asp

http://www.engr.psu.edu/iec/abe/control/pulsed_light.asp


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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.


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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.


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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.

References

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2. Brown, R. C., & D. Wake (1991). "Air filtration by interception -- theory and

experiment." Journal of Aerosol Science 22(2): 181-186.


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3. Chang, J. C. S., K.K.Foarde & D.W.VanOsdell (1996). "Assessment of fungal

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and gas filtration for the brewing process." Brewers Digest 65(4): 33-35.

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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."


32. Stechkina, I. B., and A.A.Kirsch (1994). "Multistage high efficiency air filtration."


33. Straja, S., and R.T.Leonard (1996). "Statistical analysis of indoor bacterial air

concentration and comparison of four RCS biotest samplers." Environment


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.


21

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.


22

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


23

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.

http://www.engr.psu.edu/iec/abe/publications/math_modeling.pdf

http://www.engr.psu.edu/iec/abe/publications/math_modeling.pdf


24

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.


25

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.


26

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.


27

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).


28

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).


29


30

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.


31

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.


32

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

of Escherichia coli.” Journal of General Microbiology 49: 115-117.

4. de Jong, J. C., K.C.Winkler (1968). “The inactivation of poliovirus in aerosols.”


5. Harper, G. J. (1961). “Airborne micro-organisms : survival tests with four viruses.”


6. Benbough, J. E., A.M.Hood (1971). “Viricidal activity of open air.” Journal of Hygiene

69: 619-626.

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. 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.

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.”


11. Blowers, R. and B.Crew (1960). “Ventilation of operating-theatres.” Journal of

Hygiene 58: 427-448.

12. Liu, R., and M.A.Huza (1995). “Filtration and indoor air quality: a practical

approach.” ASHRAE Journal 37(2): 18.

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





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.


33

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

room environments, I, II, III.” J. Bacteriol. 42: 321-366.

24. ASHRAE (1989). Standard 62R: Ventilation for acceptable indoor air quality,

ASHRAE.

25. Ager, B. P. and J. A. Tickner (1983). “The control of microbiological hazards

associated with air conditioning and ventilation systems.” Ann. Occup. Hyg. 27(4):

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.


34

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%.


35

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.


36

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.


37

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.


38

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.


39




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.)


40

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.


41

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.


42

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.


43

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


44

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


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

mailto:[email protected]


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.


46

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


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


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.


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.


48

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.


49

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


50

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


51

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


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.


52

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


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


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


53

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.


54

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.


55

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.


56

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


57

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.

http://www.purepulse.com/

http://www.wektec.com/


58

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.


59

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.


60

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


61

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.


62

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


63

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