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
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
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
IAQ – Related Illness
and related diseases Respiratory and skin allergies Chemical poisoning Radiation-related sickness Odor-related discomfort
Pneumonia
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
IAQ Evaluation
visit Interview exposed group Monitor air quality and ventilation Relate observations to data and problem Make recommendations for abatement
Site
IAQ Abatement (general)
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)
Reduce
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)
Shower Curtain Mold
Source of Allergins
Ventilator
Influent Vent for Ventilator
Kitchen Vent
Bathroom Vent
Main Return With Microfilter
HEPA Ventilation Unit
Vacuum With HEPA Filter
Vacuum Filters (paper and HEPA)
Original Apparatus Attached to A/C System
Objectives
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
To
Biofilm Growth in A/C Systems
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
Effects of Biofilm
Health
effects
allergies, asthma hyper-sensitivity pneumonitis legionnaire's disease sick building syndrome
Decreased
efficiency of heat exchanger
Ozone
oxidant and powerful disinfectant Decomposes quickly Adverse health effects
Strong
eye irritation, headaches, dizziness, coughing, tightness in chest, premature aging of the lung
for water disinfection Opportunities in air treatment
Used
Patent 5,286,447 (1994) K. F. Fannin and D. P. Chynoweth
and Apparatus for Controlling Microbial Growth on Condensation Coils” Principles
“Method
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
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
Determine
Original Apparatus Attached to A/C System
Test Apparatus
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
Ozone Exposure
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
One
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
Trial Overview
Trial Ozone Conc. (mg/L) 0.0044 0.0044 0.0044 0.0044 0.0273 Duration (min) 20 20 120 60 60 Frequency (per day) 2 12 2 2 2 Media Conc. (%) 100 100 100 10 100
1 2 3 4 5
Trial 3
Frequency: 2/day Duration: 120 min Serratia marcescens
Trial 3
Frequency: 2/day Duration: 120 min Serratia marcescens streak
Trial 3
Frequency: 2/day Duration: 120 min Aspergillus niger
Trial 3
Frequency: 2/day Duration: 120 min Aspergillus niger streak
Summary of Trials With One Ozone Generator; Inoculum Serratia or Aspergillus
Trial 1 2 3 4 5 Conc. Dur. (mg/L) (min) 0.0044 20 0.0044 0.0044 0.0044 0.0273 20 120 60 60 Freq. (per day) 2 12 2 2 2 Serratia Growth limited limited none limited none Aspergillus Growth limited limited limited limited limited
Summary of Trials With Two Ozone Generators; Inoculum, Serratia or Aspergillus
Trial 6 7 8 Conc. Dur. (mg/L) (min) 0.018 0.018 0.018 15 60 60 Freq. (per day) 24 2 2 Serratia Growth none limited limited Aspergillus Growth none limited limited
Summary of Trials With Two Ozone Generators; Natural Airborne Inoculum
Trial 9 10 11 Conc. Dur. (mg/L) (min) 0.018 0.018 0.018 30 30 30 Freq. (per day) 4 6 12 Bacterial Growth none none none Fungal Growth limited none none
Summary of Trials With Two Ozone Generators; Natural Airborne Inoculum
Trial 12 13 14 15 Conc. Dur. (mg/L) (min) no ozone 0.018 0.018 0.018 30 30 30 30 Freq. (per day) 2 2 2 2 Bacterial Growth heavy none none none Fungal Growth heavy limited limited none
Effect of Exposure Time on Chamber Ozone Conc. (two ozonaters in series)
0.02 0.015 0.01 0.005 0 0 10 20 30 40 50 Time, min
Ozone, mg/L
Natural Air Flora Control (no ozone; 2X per day for 30 min;)
Natural Air Flora Experimental (ozone, 0.018 mg/L; 2x per day for 30 min.)
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.
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).
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
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