Influence of Ozone Air Treatment on Growth of Bacteria and Fungi in Air Conditioning Systems

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Influence of Ozone Air Treatment on Growth of
Bacteria and Fungi in Air Conditioning Systems

• David P. Chynoweth
• Agricultural and Biological Engineering Dept.
• University of Florida, Gainesville, FL

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Scope of Presentation

• Objectives
• Indoor air quality problem (causes, effects,
  abatement)
• Biofilms in A/C systems
• Ozone treatment system
• Experimental system
• Results and discussion
• Conclusions

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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

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IAQ Related Illness

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

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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

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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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Objectives

• To demonstrate the effect of intermittent ozone
  treatment on growth of microorganisms in air
  conditioning systems
• To determine the effect of ozone concentration,
  exposure time, and exposure frequency on
  microbial growth

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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

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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
• Decomposes quickly
• Adverse health effects
• eye irritation, headaches, dizziness, coughing,
  tightness in chest, premature aging of the lung
• Used for water disinfection
• Opportunities in air treatment

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Patent 5,286,447 (1994) K. F. Fannin and D. P.
Chynoweth

• Method and Apparatus for Controlling Microbial
  Growth on Condensation Coils
• Principles
• Intermittent treatment with ozone
• Controller shuts off A/C, isolates treatment
  zone, treats with ozone, evacuates ozone, and
  turns A/C back on
• Vary ozone concentration, treatment duration, and
  treatment frequency

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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

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Original Apparatus Attached to A/C System
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Test Apparatus
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Experimental Procedure

• Inoculum
• 1) spread plates of diluted bacterium Serratia
  marcescens or fungus Aspergillus niger spread on
  Petri dishes,
• 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 Exposure

• One or two ultraviolet ozone generators
• Airflow rate 1.5 cfm
• Ozone concentrations
• 0.0044 mg/L
• 0.018 mg/L
• Frequency 2, 4, 6, 12, or 24 times per day
• Duration 15, 20, 60, or 120 min

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Ozone Measurement Procedure

• Potassium Iodide
• Add 10 mL of 1 N sulfuric acid
• 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
• Titrate with 0.003 N thiosulfate solution, add 2
  mL starch indicator just before clear endpoint
• Drager Tubes

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Trial Overview
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Results of Trial 1Frequency 2/day Duration 20
min
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Trial 3Frequency 2/day Duration 120
minSerratia marcescens
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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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Summary of Trials With One Ozone Generator
Inoculum Serratia or Aspergillus
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Summary of Trials With Two Ozone Generators
Inoculum, Serratia or Aspergillus
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Summary of Trials With Two Ozone Generators
Natural Airborne Inoculum
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Summary of Trials With Two Ozone Generators
Natural Airborne Inoculum
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Effect of Exposure Time on Chamber Ozone Conc.
(two ozonaters in series)
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Natural Air Flora Control(no ozone 2X per day
for 30 min)
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Natural Air Flora Experimental (ozone, 0.018
mg/L 2x per day for 30 min.)
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Conclusions (1)

• Ozone is an effective method for prevention of
  growth of bacteria and mold in A/C systems.
• Concentration of 0.0044 mg/L, duration of 30 min,
  and frequency of 2 times per day prevented
  visible accumulation of microbial biofilm in an
  A/C unit over a period of six months
• Concentration of 0.0044 mg/L, duration of 120
  min, and frequency of 2 times per day resulted in
  total inhibition of Serratia and partial
  inhibition of Aspergillus.

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Conclusions (2)

• Concentration of 0.018 mg/L, duration of 15 min
  and frequency of 24 times per day resulted in
  total inhibition of Serratia and Aspergillus.
• Concentration of 0.018 mg/L, duration of 15 min
  and frequency of 6 times per day resulted in
  total inhibition of natural airborne organisms.
• Concentration of 0.018 mg/L, duration of 30min
  and frequency of 2 times per day resulted in
  total inhibition of natural airborne organisms
  (only partial inhibition of fungi was observed in
  one run under these conditions).

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Future Work

• Evaluate higher ozone concentrations
• Develop inhibition model based on ozone
  concentration, treatment time, and treatment
  frequency
• Conduct microbial analyses in actual A/C systems
• Commercialize