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One Odour Unit-Precisely how can an Odour Unit be measured?

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One Odour Unit-Precisely how can an Odour Unit be measured?

One Odour Unit-Precisely how can an Odour Unit be measured?

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    One Odour Unit-Precisely how can an Odour Unit be measured? One Odour Unit-Precisely how can an Odour Unit be measured? Presentation Transcript

    • One Odour Unit-Precisely how can an Odour Unit be measured? WEF/A&WMA Odors and Air Pollutants 2010 Presented by: Anna H. Bokowa ORTECH Environmental Mississauga, Ontario CANADA
    • Overview
      • Introduction
      • Factors influencing off-site odour concentration determinations
      • Case studies
      • Conclusions
      • Odour - nuisance in most jurisdictions in Canada, Australia, United States
      • A nuisance can be demonstrated by verifiable complaints and by odour testing programs
      • In Ontario, Canada, target 1 ou at the any sensitive receptor (based on predicted odour concentrations using measured odour emission rates and dispersion modelling) or ambient measurements
      Introduction
    • Introduction (cont’d.)
      • In Queensland, Australia, requirement of 0.5 ou for tall stacks or 2.5 ou for short stacks
      • How precisely can we measure or predict odour units?
      • Is it possible to measure or predict 0.5 ou or 1 ou?
      • 1 ou might be 10 ou or greater and will depend on several factors (selection of sources, sampling methodology, analysis, dispersion modelling)
      • The losses of odour might be significant if proper sampling methodology is not used
      • Careful selection of all potential odour sources in the plant (point, area, fugitive)
      • Sampling methodology
      • Time period between the collection of the samples and their evaluation
      • Selection of the olfactometer used for odour evaluations
      • Panelists selection and their sensitivity
      • Dispersion modelling used
      Factors Influencing Off-Site Odour Concentration Determinations
      • Important to include all sources in the assessment (point sources, area sources, fugitive sources)
      • Fugitive sources are often omitted
      • Predicted odour concentrations using modelling are lower than actual or measured ambient levels when sources are omitted
      • Cases when significant sources were omitted and predicted concentrations were 10 ou as a maximum but measured off site odour was 200 ou
      • Good practice to combine source testing with ambient sampling
      Factor 1: Selection of all Potential Odour Sources
      • Mushroom/Compost Facility- operation carried on as a normal farm practice?
      • Is it normal to be exposed to 200 ou at a residence
      • Facility assessed and predicted off-site concentration only 10 ou as the worst case scenario (one consultant)
      • but measured off site 200 ou (by ambient sampling and odour evaluation by another consultant)
      • Who is right? Good practice to combine source testing with ambient monitoring
      Factor 1: Example of Missing Sources
      • Point Sources
      • In Ontario the methodology is very strict
      • and requires sampling at a dilution when the minimum odour loss occurs during collection of the samples (optimum dilution)
      • In the predilution technique, emission gases are diluted with nitrogen in order to minimize the loss of odourant by adsorption, condensation and oxidation
      • Most European countries use the dilution technique when collecting samples from point sources ( hot, humid)
      Factor 2: Sampling Methodology
    • Factor 2 (cont’d.): Sampling Methodology
      • Point Sources
      • Only in the US, the dilution techniques is not used in most states
      • Dilution technique is very important especially for hot, humid sources
      • The loss of the odour might be significant when dilution on site is not used
      • Therefore the predicted concentration of 1 ou may actually be much higher
      • 1 ou measured might actually be 16 ou
    • Factor 2: Effect of Different Techniques used For Collection of Samples-Point Sources * 16X lower value Sampling Location Sample No. Predilution Raw ODTV (ou) Net ODTV (ou) Geometric Mean Net ODTV (ou) Source 1 1 50 651 32,550 2 50 668 33,400 34,294 * 3 50 742 37,100 1 40 636 25,440 1 60 336 20,160 1 1 2130 2,130 2 1 1969 1,969 2,075 * 3 1 2130 2,130
    • Factor 2: Effect of Different Techniques used For Collection of Samples- Point Sources * 13X lower value Sampling Location Sample No. Predilution Raw ODTV (ou) Net ODTV (ou) Geometric Mean Net ODTV (ou) Source 2 1 40 19 760 1 30 50 1,500 2 30 56 1,680 1,588 * 3 30 53 1,590 1 20 57 1,140 1 1 123 123 2 1 121 121 124* 3 1 128 128
    • Factor 2: Effect of Dilution-Point Sources Source Predilution Net Odour (ou) Difference 1 50 34,300 16X None 2,025 2 30 1,600 13X None 124
      • Different methods: flux chamber method and wind tunnel method
      • In recent years, several studies in Canada and Europe had shown a significant difference in the results
      • Wind tunnel technique is a more appropriate method and gives much higher results (up to 11 times higher)
      Factor 2: Area Sources
    • Factor 2: Study 2 Comparison of Wind Tunnel and Flux Chamber Method Predilution Geometric Mean of OTV Samples (ou) Emission Rate (ou/s/m 2 ) Difference Wind Tunnel None 760 62 11X Flux Chamber 20 19,860 5.1
      • In US odour is still regulated based on the ambient levels
      • Different methods for ambient odour level assessments: collection of ambient samples and evaluation by an odour panel (in Ontario common approach)
      • Scentometers or Nasal Ranger instruments- mostly in US
      Factor 2: Ambient Assessment
      • Scentometers-1959 - instrument should not be used any more due to the same deficiency
      • Results obtained by the Scentometer or Nasal Ranger are based on one person readings and their sensitivity.
      • No assurance that the operators nose has re-established its peak level of sensitivity, therefore the readings would be lower than results obtained by collecting ambient samples and analysis
      • 1 ou measured might actually be up to 13 ou
      Factor 2 (cont’d.): Ambient Assessment
    • Study 3 Effect of Techniques used for Ambient Assessments
    • Study 3 Effect of Techniques used for Ambient Assessments
      • Losses of odour might be significant, when compounds are not stable (H 2 S)
      • Analysis should be done within few hours
      • ORTECH performs analysis within 6 hours (preferably) but not exceeding 12 hours
      Factor 3: Time between the sampling and odour evaluation
    • Factor 4: Types of Olfactometers
      • Different types of olfactometers: one station and multiple station
      • Multiple station-evaluation of samples at the same time by 6 or 8 panelists (ORTECH has 8)
      • One station-evaluation done by one panelist at a time (greater error in the results due to several factors such as uncertainty in using the same dilution for all panelists, short mixing time, possible contamination of the system with so many dilution changes for each panelist)
      • European Standard EN 13725 :2003 requires panelists with an average sensitivity of 20 ppb to 80 ppb for n- butanol
      • One laboratory uses panelists with average sensitivity of 20-30 ppb and second with 70-80 ppb
      • Difference in the results by a factor of about 3-4 times
      • 1 ou measured might actually be 3 ou or 4 ou just by selecting the panelists
      Factor 5: Panelist Selection
      • Compliance with odour regulations such as 1 ou or 0.5 ou is difficult to demonstrate unless a proper sampling methodology is developed, approved and followed by all consultants
      • 1ou might be very easily 10 ou or greater and will depend on factors such as:
      • Methodology used for the collection of the samples, their evaluation, time elapsed between sampling and analysis, omitting significant odour sources at the plant, ambient techniques for assessing ambient odours
      Conclusions
      • When assessing odours at the facility it is important to include all sources in the plant (point, area, fugitive)
      • Proper sampling methodology is required especially when sampling at hot, humid sources (dilution technique) to avoid any odour losses during sampling
      • Undilution technique should not be used for collection of samples from hot , humid sources
      • Limit the time between sampling and evaluations
      Conclusions (cont’d.)
      • When sampling at area sources a wind tunnel technique is the preferred technique under conditions where the wind might have some influence on emissions
      • When assessing ambient levels the technique with collection of ambient samples and evaluation by a dynamic olfactometry is the preferred method
      • Scentometers should be not used due to their deficiencies
      Conclusions (cont’d.)
    • Final Comment
      • Regulation of 1 ou or 0.5 ou is unrealistic unless step by step sampling and analysis methodologies are followed
    • Contact Information Anna H. Bokowa, M.Sc. Manager, Odour Assessment ORTECH Environmental 804 Southdown Road Mississauga, Ontario L5J 2Y4 1-877-774-6560, Ext. 669 [email_address]