Ozone Treatment for Prevention of Microbial Growth in Air Conditioning Systems
David P. Chynoweth
Agricultural & Biological Engineering UNIVERSITY OF FLORIDA
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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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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
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IAQ – Related Illness
and related diseases Respiratory and skin allergies Chemical poisoning Radiation-related sickness Odor-related discomfort
Pneumonia
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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
visit Interview exposed group Monitor air quality and ventilation Relate observations to data and problem Make recommendations for abatement
Site
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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
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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
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
Collection
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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 Gaseous property facilitates efficient dispersion Decomposes quickly to non-toxic products Adverse health effects
Used for water disinfection (well studied) Opportunities in air treatment (not well studied or widely used)
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eye irritation, headaches, dizziness, coughing, tightness in chest, premature aging of the lung
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Physiological Effects of Ozone on Humans
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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Permissible
Research Objectives
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
Determine
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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) radiationbased 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 <10%> 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
Ozone Concentration vs. Time
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Ozone Concentration(PPM)
30 25 20 15 10 5 0 0 5 10 15 Time (minutes) 20 25 30
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Frequency: 2/day Duration: 120 min Serratia marcescens streak
Trial 3
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Frequency: 2/day Duration: 120 min
Trial 3
Aspergillus niger
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Frequency: 2/day Duration: 120 min Aspergillus niger streak
Trial 3
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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
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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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Prevention of Growth in Air Handling Systems
Commercial Applications
space craft, space stations
NASA:
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)
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Acknowledgements
Funding:
savings Researchers:
NASA/UF ES CSTC salary
Alison Vergari, Undergrad. Internship Aakash Khurana, Master’s Thesis
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