Ozone Treatment for Prevention of Microbial Growth in Air Conditioning Systems

1
Ozone Treatment for Prevention of Microbial
Growth in Air Conditioning Systems

• David P. Chynoweth
• Agricultural Biological Engineering
• UNIVERSITY OF FLORIDA

2
Scope of Presentation

• Objectives
• Factors affecting indoor air quality
• Biofilms in A/C systems
• Ozone treatment system
• Experimental system
• Results and discussion
• Conclusions

3
Indoor Air Quality Is Affected By

• Accumulation of microorganisms in A/C systems
• Outdoor microorganisms
• Contamination of building materials
• Decreased air exchange from design changes to
  conserve energy
• Less ventilation due to increased use of A/C
  systems

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Categories of Indoor Air Pollutants

• Pathogenic microorganisms (bacteria, molds and
  viruses)
• Allergenic microorganisms (bacteria, molds)
• Respirable particles (smoke, dust, pet hairs,
  dust mites, etc.)
• Volatile organic compounds (formaldehyde, cooking
  products, hair sprays, pesticides)
• Radon and radon decay products

5
IAQ Related Illness

• Pneumonia and related diseases
• Respiratory and skin allergies
• Chemical poisoning
• Radiation-related sickness
• Odor-related discomfort

6
Why Increased IAQ-Related Illness

• Decreased air exchange related to tighter
  buildings (energy conservation)
• Less ventilation to conserve on A/C and heating
• Contamination from A/C condensers
• Increase use of pesticides and other chemicals
• More time spend indoors (up to 90)
• Increased awareness of relationship between IAQ
  and illness
• Increased awareness of indoor pollutants such as
  tobacco smoke and radon

7
IAQ Evaluation

• Site visit
• Interview exposed group
• Monitor air quality and ventilation
• Relate observations to data and problem
• Make recommendations for abatement

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IAQ Abatement (general)

• Reduce sources of pollutants (general house
  cleaning, clean ducts, pet management, clean air
  conditioner)
• Humidity control (at 50)
• Increase ventilation (indoor-outdoor air
  exchange, vent cooking gasses, reduce indoor dead
  zones
• Air cleaning (removal of airborne particulates
  and chemicals)

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IAQ Abatement (specific)

• Vacuum with HEPA or outside-exhausting system
• Use high efficiency return air filters
• Use on-line or room air HEPA filters
• Clean A/C condensation coils and pan 2X per year
• Ventilate dwelling
• Dehumidify (50)
• Eliminate moisture (leaks, condensation,
  bathrooms, kitchen)

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Shower Curtain Mold
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Source of Allergins
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Ventilator
13
Influent Vent for Ventilator
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Kitchen Vent
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Bathroom Vent
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Main Return With Microfilter
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HEPA Ventilation Unit
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Vacuum With HEPA Filter
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Vacuum Filters (paper and HEPA)
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Biofilm Growth in A/C Systems
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Causes of Biofilm

• Collection of water from condensation coil on
  coil and in drip pan
• Impingement of organic matter from airborne
  particles
• Resident microorganisms from air
• Growth of microorganisms on organic matter

22
Effects of Biofilm

• Health effects
• allergies, asthma
• hyper-sensitivity pneumonitis
• legionnaire's disease
• sick building syndrome
• Decreased efficiency of heat exchanger

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Ozone

• Strong oxidant and powerful disinfectant
• Gaseous property facilitates efficient dispersion
• Decomposes quickly to non-toxic products
• Adverse health effects
• eye irritation, headaches, dizziness, coughing,
  tightness in chest, premature aging of the lung
• Used for water disinfection (well studied)
• Opportunities in air treatment (not well studied
  or widely used)

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Physiological Effects of Ozone on Humans

• Permissible short-term exposure limit of 0.3 PPM
  for less than 15 minutes (OSHA ,1975)
• 0.1-1PPM-Headache, Throat Dryness, Respiratory
  Irritation
• 1-100 PPM-Tiredness, Lack of Appetite,
  Respiratory Problems
• Higher concentrations- Throat Irritation,
  Hemorrhaging, Pulmonary edema

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Research Objectives

• Determine quantitative effects of ozone treatment
  on microbial growth in A/C systems
• Find the optimum combination of ozone exposure
  frequency, duration, and concentration
• Develop engineering design data base

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Original Apparatus Attached to A/C System
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Original Test Apparatus
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Laboratory Test Apparatus
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Ozone Generation

• Ultravoilet (UV) radiation- based ozone
  generators

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Experimental Procedure

• Inoculum
• 1) spread plates of diluted bacterium Serratia
  marcescens or fungus Aspergillus niger spread on
  Petri dishes (dilute lt10gt broad spectrum media)
• 2) streak plates of Serratia or Aspergillus
• 3) impingement of room air natural flora
• Placed experimental and control dishes in test
  chamber incubated 3-5 days
• Set ozone treatment concentration, duration, and
  frequency

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Ozone Measurement Procedure

• Potassium Iodide
• Place 400 mL of 2 KI in the absorber and insert
  gas diffusion tube
• Connect sampling line and pass 4.6 cfm ozonated
  air through KI solution for 10 min
• Add 10 mL of 1 N sulfuric acid
• Titrate with 0.003 N thiosulfate solution, add 2
  mL starch indicator just before clear endpoint
• Drager Tubes (used for rapid verification)
• Ozone Analyzer (too sensitive)

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Times Required to Stabilize Ozone Concentration
in an Exposure Chamber
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Trial 3Frequency 2/day Duration 120
minSerratia marcescens streak
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Trial 3Frequency 2/day Duration 120
minAspergillus niger
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Trial 3Frequency 2/day Duration 120
minAspergillus niger streak
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Comparison of Ozone Treated Plate (left) with
Untreated Plate (right)
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Previous Work at UF
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Previous Work at UF (cont.)
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Inhibition Design Matrix
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Conclusions

• Ozone treatment is effective in prevention of
  growth of microorganisms in A/C systems
• One 15-min treatment per day of ozone exposure at
  45 PPM is effective
• One 30-min treatment per of ozone exposure at 25
  PPM is effective

41
Patent

• Fannin, K. F. and Chynoweth, D. P., "Method and
  Apparatus for Controlling Microbial Growth on
  Condensation Coils," U.S. Patent 5,286,447,
  February 15, 1994.

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Commercial ApplicationsPrevention of Growth in
Air Handling Systems

• NASA space craft, space stations
• Terrestrial homes, buildings, automobiles,
  buses, ships, trains, aircraft

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Suggestions for Future Work

• Mechanisms of microbe reduction growth versus
  death
• Field trials in real A/C systems
• Reducing ozone concentration in exhaust or
  decomposing ozone into oxygen thermally and/or
  by catalytic means
• Cost economics study to determine commercial
  feasibility (ES CSTC effort)
• Commercialization (ES CSTC effort)

44
Acknowledgements

• Funding NASA/UF ES CSTC salary savings
• Researchers
• Alison Vergari, Undergrad. Internship
• Aakash Khurana, Masters Thesis