AIR FILTER DISINFECTION USING MICROWAVE RADIATION

A&WMA Int. Specialty Conference: Leapfrogging
Opportunities for Air Quality Improvement, Xi’an, China
AIR FILTER DISINFECTION USING
MICROWAVE RADIATION
Brian Damit, Chang-Yu Wu, Qi Zhang, Myung-Heui Woo,
Hyoungjun Park, Wolfgang Sigmund, Kyle Ulmer, Yu-Mei Hsu
2010/05/11
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Bioterrorism/Airborne Pathogens
Intentional use of bioaerosols to
produce death or disease in
humans, animals or plants
Public Health: Spread of airborne
pathogens such SARS, flu
http://www.lewrockwell.com/orig2/miller6.html
http://www.cnn.com/SPECIALS/2003/sars/
http://www.usatoday.com/news/nation/2002/06/14/anthrax.htm
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Filtration
• Respirators for personal protection & HVAC
(Heating, Ventilation and Air Conditioning)
filters for collective protection
• Drawbacks: breathing difficulty, growth on
filter, re-entrainment, hazardous disposal;
respirator shortage during pandemic
www.indiamart.com/.../industrial-filters.html
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http://www.usatoday.com/news/nation/2002/06/14/anthrax.htm
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Objectives
• Develop microwave assisted filter regeneration
technology to inactivate airborne pathogens
without damaging the filter
– Assess the feasibility of microwave irradiation for
disinfection of air filters
– Evaluate the effects of operating parameters
(power level, irradiation time)
– Investigate the utilization of microwave absorbing
support for enhanced performance
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Filter
Filter: Polyacrylonitrile (PAN) nanofiber filter, df = 195 nm. Filters
fabricated by UF Material Science using electrospinning .
2 µm
Scale: 2 µm, taken with JEOL JSM 6400 SEM.
For Heating:
(high electric permittivity)
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SiC fibermat
SiC disk
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Microwave and Reactor
Microwave: Panasonic Model NN-T945SF, continuous irradiation
Inside the reactor:
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Testing Microorganisms
• Testing Microorganisms:
– Escherichia coli (da = 0.8 µm)
– Bacillus subtilis endospores (da = 0.9 µm)
• These surrogate microbes are
physically and biologically similar to
E. coli
pathogenic microbes.
B. anthracis
Images obtained from http://www.cdc.gov/.
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On-Filter Static Microbe Inactivation
Before in-flight experiments, static on-filter inactivation tests
were conducted to explore feasibility and to establish a baseline.
These results gave indication that microbe inactivation on the
filter during in-flight tests would be possible.
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In-flight Inactivation
 CFU exp
Log Inactivation = − log 
 CFU control
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
 = − log( survival )

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In-flight E. coli results
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In-flight B. subtilis spore results
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Reduced Flow Results
With less heat loss to the flow, the filter is able to
achieve a greater temperature and destroy spores
more effectively.
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Power
Time application
Inactivation with
no flow reduction
750 W
1.25 min/cycle
75.15%
Aerosol & Particulate Research Lab
Inactivation with
50% flow
reduction
94.25 %
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HVAC Filter
Filter Medium
Filtrete 1250 from 3M
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Microorganism
E. coli
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HVAC Filter with Microwave Irradiation
↑ irradiation time
↑ deactivation
↑ loading system relative humidity
↑ deactivation
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Conclusions
• Greater than 4 log inactivation of E. coli
and > 2 log inactivation of endospores.
• Reduced flow conditions increased filter
temperature and microbe inactivation.
• SiC support greatly enhances MW assisted
inactivation
• The results show promise in regenerating
air filters with microwave radiation.
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Acknowledgments
• This work was funded by the Defense Threat
Reduction Agency (DTRA) project grant #
BB07PRO013.
• Brian Damit is thankful for the National Science
Foundation (NSF) Bridge to the Doctorate
Fellowship.
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Thank you!
Questions?
Chang-Yu Wu
University of Florida
Department of Environmental Engineering Sciences
352-392-0845; cywu@ufl.edu
Microwave Disinfection
• Electromagnetic radiation of wavelength 1 mm – 1
m, frequencies from 300 MHz to 3 GHz; domestic
MW oven uses 2.45 GHz
• Rapid fluctuations in the electromagnetic spectrum
cause dipole (e.g. water molecules) to repeatedly
change orientation; friction between molecules
translates into heat
• Past studies conducted for disinfection in water, not
in air filtration
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Respirator Shortage during Pandemic Influenza
• “CDC estimates that in the event of a severe influenza
pandemic at least 1.5 billion medical masks would be
needed by the healthcare sector and an additional 1.1
billion would be needed by the public. Demand for the
N95 respirator by the healthcare sector could exceed
90 million for a 42-day outbreak.”
• Possible solution: decontaminate the respirator and
reuse it
Q: How?
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Comparisons to Past Study (E. coli)
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In-flight MS2 virus results
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