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, Alison Vergari, Paul Lane,
  and Kerby F. Fannin
• Agricultural and Biological Engineering Dept.
• University of Florida, Gainesville, FL

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Scope of Presentation

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

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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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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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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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Health Effects

• Hyper-sensitivity
• Pneumonitis
• Sick Building Syndrome
• Legionnaire's Disease
• Asthma
• Allergies

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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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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
• 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

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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