one odour unit-precisely how can an odour unit be measured?
DESCRIPTION
One Odour Unit-Precisely how can an Odour Unit be measured?TRANSCRIPT
1
One Odour Unit-Precisely how can an Odour Unit be
measured?WEF/A&WMA
Odors and Air Pollutants 2010
Presented by:
Anna H. BokowaORTECH Environmental
Mississauga, OntarioCANADA
Overview• Introduction• Factors influencing off-site odour
concentration determinations• Case studies• Conclusions
2
3
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
4
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
1.Careful selection of all potential odour sources in the plant (point, area, fugitive)
2.Sampling methodology 3.Time period between the collection of the
samples and their evaluation4.Selection of the olfactometer used for
odour evaluations5.Panelists selection and their sensitivity6.Dispersion modelling used
5
Factors Influencing Off-Site OdourConcentration 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
6
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
7
Factor 1: Example of Missing Sources
8
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 MethodologyPoint 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
9
10
Factor 2: Effect of Different Techniques used
For Collection of Samples-Point SourcesSamplin
gLocation
SampleNo. Predilutio
n
Raw ODTV(ou)
NetODTV(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
* 16X lower value
11
Factor 2: Effect of Different Techniques usedFor Collection of Samples- Point Sources
Sampling
Location
SampleNo. Predilutio
n
Raw ODTV(ou)
NetODTV(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
* 13X lower value
Source PredilutionNet Odour
(ou) Difference
1 50 34,300 16X
None 2,025
2 30 1,600 13X
None 124
12
Factor 2: Effect of Dilution-Point Sources
13
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
MethodPredilutio
n
Geometric Mean of
OTV Samples
(ou)
Emission Rate
(ou/s/m2)Differenc
e
Wind Tunnel None 760 62 11X
Flux Chamber 20 19,860 5.1
14
Factor 2: Study 2 Comparison of Wind Tunnel and Flux Chamber
15
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
16
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
17
Study 3Effect of Techniques used for Ambient
AssessmentsLocation Sample Number Odour Concentration Nasal Ranger Ratio Nasal Ranger
determined by on site Odour Concentration in the bag
olfactometer in the Bag ou D/T to Nasal Ranger D/T
Site 1Location 1 Sample 1 48 7 6.9 4
Sample 2 87 7 12.4 4Sample 3 73 7 10.4 4
Location 2 Sample 1 91 15 6.1 7
Sample 2 86 15 5.7 7Sample 3 60 7 8.6 4
Site 2Location 1 Sample 1 26 4 6.5 2
Sample 2 34 4 8.5 2Sample 3 48 4 12.0 NM*
Location 2 Sample 1 38 4 9.5 2
Sample 2 52 4 13.0 2Sample 3 122 NM* ND** 7
18
Study 3Effect of Techniques used for Ambient Assessments
Location Sample Odour Concentration Nasal Ranger Ratio Nasal Ranger Readings
Number determined by Readings Odour Concentration in the Bag
olfactometer on site in the Bag ou D/T to Nasal Ranger D/T
Location 1 Sample 1 164 60 2.7 30Sample 2 128 60 2.1 15Sample 3 178 60 3.0 15
Location 2 Sample 1 262 100 2.6 30
Sample 2 186 60 3.1 15Sample 3 207 60 3.5 30
19
Losses of odour might be significant, when compounds are not stable (H2S)
Analysis should be done within few hours
ORTECH performs analysis within 6 hours (preferably) but not exceeding 12 hours
Factor 3: Time between the samplingand 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)
21
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
22
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
23
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
24
Conclusions (cont’d.)
Final CommentRegulation of 1 ou or 0.5 ou is unrealistic unless step by step sampling and analysis methodologies are followed
26
Contact Information
Anna H. Bokowa, M.Sc.Manager, Odour
Assessment
ORTECH Environmental804 Southdown RoadMississauga, Ontario
L5J 2Y41-877-774-6560, Ext. 669