Title: Influence of Ozone Air Treatment on Growth of Bacteria and Fungi in Air Conditioning Systems
1Influence 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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2Scope of Presentation
- Objectives
- Factors affecting indoor air quality
- Biofilms in A/C systems
- Ozone treatment system
- Experimental system
- Results and discussion
- Conclusions
3Objectives
- 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
4Indoor 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
5Biofilm Growth in A/C Systems
6Causes 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
7Effects of Biofilm
- Health effects
- allergies, asthma
- hyper-sensitivity pneumonitis
- legionnaire's disease
- sick building syndrome
- Decreased efficiency of heat exchanger
8Health Effects
- Hyper-sensitivity
- Pneumonitis
- Sick Building Syndrome
- Legionnaire's Disease
- Asthma
- Allergies
9Ozone
- 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
10Research 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
11Original Apparatus Attached to A/C System
12Test Apparatus
13Experimental 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
14Ozone 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.
15Ozone 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
16Trial Overview
17Results of Trial 1Frequency 2/day Duration 20
min
18Trial 3Frequency 2/day Duration 120
minSerratia marcescens
19Trial 3Frequency 2/day Duration 120
minSerratia marcescens streak
20Trial 3Frequency 2/day Duration 120
minAspergillus niger
21Trial 3Frequency 2/day Duration 120
minAspergillus niger streak
22Summary of Trials With One Ozone Generator
Inoculum Serratia or Aspergillus
23Summary of Trials With Two Ozone Generators
Inoculum, Serratia or Aspergillus
24Summary of Trials With Two Ozone Generators
Natural Airborne Inoculum
25Summary of Trials With Two Ozone Generators
Natural Airborne Inoculum
26Effect of Exposure Time on Chamber Ozone Conc.
(two ozonaters in series)
27Natural Air Flora Control(no ozone 2X per day
for 30 min)
28Natural Air Flora Experimental (ozone, 0.018
mg/L 2x per day for 30 min.)
29Conclusions (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.
30Conclusions (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).
31Future 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