measuring and managing odours - the royal society of ... and managing odours: technical and...

Measuring and managing odours: Technical and practical issues

Nick Jones, OdourNet UK Ltd

Scope Provide a technical definition of ‘odour nuisance’ and describe the key

factors that contribute to its development.

Describe how each of these factors can be considered and how therisk of odour nuisance impact can be assessed in practical terms.

Briefly explain how data obtained from such assessments can be used to assist legal cases, and in defining odour management and control solutions.

What is ‘odour nuisance’? In technical terms, the commonly applied definition

for odour nuisance is:

‘…the cumulative effect on humans, of repeated events of annoyance caused by exposure to odours, over an extended period of time, that leads to modified or altered behaviour.’

Important points to take from that definition are:

Odour nuisance is not a push button reaction.

Exposure generates a negative reaction.

Behavioural changes elicited by nuisance can be passive or active.

Factors that influence development In practical terms, the main factors that determine the development

of nuisance can be usefully summarised by the acronym FIDOL.

Frequency of exposure.

Intensity (or strength) of exposure.

Duration of exposure.

Offensiveness or character of odour.

Location sensitivity.

Development of nuisance is therefore directly influenced by:

Characteristics of the odours released from a given source.

The effects of atmospheric dispersion and dilution as odours travel from the source to the point of detection.

The characteristics of the person or persons exposed.

Factors to consider during assessment

Atmospheric dispersionSource characteristics Receptor sensitivity

Nature of each activity

The type of odour released

The quantity of odour released

Frequency and duration of release

Wind speed and direction

Atmospheric turbulence

Distance to receptor

Type (residential / industrial)

Context

Exposure history

Perception towards source

Identification of odour sources

The first step to assessment is to identify specific operations or activities that have the potential to generate odours that will be detectable offsite.

Define the physical characteristics of the source and mechanism for release (e.g. location, dimensions, source type, etc).

Define the operational factors that influence odour generation and release e.g.

Operational hours.

Processing rates.

Start-up and shut down.

Process variability.

Source characterisation Once the basic characteristics of each source have been defined, it is then

necessary to quantify and characterise the odorous emissions released.

Our primary interest is to characterise the odours in terms that are relevant to human impact. i.e.

Source strength (concentration and mass emission rate).

Character of the odour and potential offensiveness.

It is also important to define the physical and chemical characteristics of each source (e.g. flow rate of air; temperature and moisture content; chemical composition) as these factors have an influence on dispersion and provide important information that can greatly assist in thedevelopment of odour management and treatment solutions.

Measurement of source strength

The preferred method for determining source strength is a sensory technique know as olfactometry (BSEN13725).

This is an ‘at source’ measurement technique that is applicable to a broad range of source types.

Olfactometry involves the determination of the overall concentration of an odour sample by presentation to a panel of observers with known acuity to odour in laboratory conditions.

The odour concentration is expressed in multiples of European Odour Units (ouE), which is similar in concept to a ‘dilution to threshold’.

Once the concentration of the odour is defined, a mass emission rate can be determined by multiplying it by the flow rate of air released from the source.

Odour character and offensiveness The fundamental principals of olfactometry (i.e. the use of trained panellists

to appraise odours) can also be applied to good effect to obtain data on the character and potential offensiveness of source odours.

The most commonly applied techniques from this perspective are:

Odour quality analysis, which describes odours by reference to a set of standardised descriptors.

Hedonic tone analysis, which describes the relative unpleasantness or pleasantness of an odour by reference to a neutral gas.

It should be noted that it is often possible to obtain a sufficient level of understanding of the character and offensiveness of the odours released through the application of common sense and by reference to published literature.

Analysis only tends to be required for unusual or particularly complex odour sources (e.g. food processes).

Alternative techniques In some circumstance, it is not possible to measure odours directly using

olfactometry (e.g. where access is restricted or for inherently diffuse sources such as land-filling operations).

In these cases, source strength can be estimated remotely by use of field assessment techniques.

This approach involves direct monitoring of the plume of odour generated by the source to determine its extent of detection down wind under defined meteorological conditions. This data is then used to back calculate an emission term using a dispersion model.

The main practical drawback of the approach is that many different conditions need to be considered to arrive at robust source estimates, and a fully standardised approach for conducting assessment is not currently available. A CEN standard is however under development.

Assessment of atmospheric dispersion Once odour emissions generated from the facility have

been characterised, this data can be used to investigate the level of odour exposure that is likely to occur around the site over the long term.

This is achieved by use of mathematical models that simulate the effect of atmospheric dispersion that occurs as odours travel from the point of release to the receptor.

In order to ensure all potential meteorological conditions are considered, dispersion modelling is typically conducting using between 3 to 5 years of actual meteorological data.

It is clearly important to ensure that the data chosen is representative of the study site.

Odour impact assessment The assessment of the impact risk is conducted by comparing the

outputs of the dispersion model to a suitable odour impact criterion.

Odour impact criteria essentially define a statistical dose of odour at which there is a risk of development of nuisance.

This dose is typically described using the technical notation

C98, 1-hour = x ouE/m3 where:

x is the limit concentration (in European odour units);

The subscript ‘1-hour’ refers to the averaging time over which the concentration is calculated.

The subscript 98 refers to the statistical basis which should be used to derive concentration values from modelled data (percentile).

When applied to the model output, the area where odour exposure levels have the potential to generate ‘nuisance’ is defined.

Odour impact criteria and FIDOL All five elements of FIDOL are reflected within the odour impact criterion to

some extent.

The Frequency and Duration of exposure elements of FIDOL are represented by the percentile element of the criterion.

The Intensity, Offensiveness and Location sensitivity elements are represented by the concentration element of the criterion.

Variations in the offensiveness of odours and in receptor sensitivity can therefore be reflected by varying the concentration element of the criterion.

However, it is important to note that impact criteria tend to be derived from empirical studies which consider the potential for impact to the most sensitive members of the population. As a result adjustments to reflect receptor sensitivity tend to be rare.

Examples of impact criteria

UK planning‘Complaints’ criterion for sewage odoursC98, 1hour = 5 ouE/m3

Criterion Application Source

C98, 1hour = 1.5 ouE/m3 Indicative criterion for highly offensive odours UK EA

C98, 1hour = 3 ouE/m3 Indicative criterion for moderately offensive odours UK EA

C98, 1hour = 6 ouE/m3 Indicative criterion for low offensive odours UK EA

UK criteria compare favourably with criterion from other European states that tend to fall within the range of C98, 1hour = 0.5 ouE/m3 to C98, 1hour = 10 ouE/m3.

What’s the use? The obvious application of this assessment approach from a legal

perspective is to assist in determining whether adverse impact or ‘nuisance’has occurred.

From this perspective, it is however important to note that technical assessments of odour impact risk may not be directly or fully compatible with regulatory or legal requirements.

The outputs of such assessment should therefore be used to inform such decisions, but conclusions should be drawn by consideration of evidence as a whole (e.g. officer observations; complaints data, etc).

A more important application of odour surveys is to gain an understanding of the problem; since once we understand it we have the ability to solve it.

Source Nature ouE/s %

Material reception

Odour A / B 12,000 8%

Process A1 Odour A 36,000 24%


Process B1 Odour B 25,500 17%


Packaging Odour C 7,500 5%

Example 1: Problem definition

Emission hierarchy

Date Observation

22/5/2010 Odour D

27/05/2010 Odour A all day

01/6/2010 Odour A

02/06/2020 Odour A

03/06/2010 Odour D


Material reception

Odour A / B 12,000 8%







Complaint Log

Emission hierarchy

Date Observation

22/5/2010 Odour D

27/05/2010 Odour A all day

01/6/2010 Odour A

02/06/2020 Odour A

03/06/2010 Odour D


Material reception

Odour A / B 12,000 8%







Complaint Log

Emission hierarchy

Example 2: Nuisance impact assessment

Location of complaints

Assessing / predicting extent of nuisance risk.

Example 2: Nuisance impact assessment


Figure presents the isopleths (i.e lines of equal odour exposure) which correlate to:

C98, 1-hour = 1.5 ouE/m3 (green)C98, 1-hour = 3 ouE/m3 (orange)C98, 1-hour = 6 ouE/m3 (blue)

Example 3: Impact assessment


Area of potential impact

In this example it can be seen that complaints correlate well with predicted exposure levels of C98,

1-hour > 3 ouE/m3

Example 3: Investigating control options

Option 1

Increase stack height

Pale orange colour represents C98, 1-hour = 3 ouE/m3 isopleth for baseline scenario

Deep orange colour represents C98, 1-hour = 3 ouE/m3 isopleth for Option 1

Example 3: Investigating control options

Option 2

Treat emissions from Process A

Pale orange colour represents C98, 1-hour = 3 ouE/m3 isopleth for baseline scenario

Deep orange colour represents C98, 1-hour = 3 ouE/m3 isopleth for Option 2

Example 3: Solution appraisal (impact)

Comparison of options

Treat emissions from Process B

Figure presents C98, 1-hour = 3 ouE/m3 for baseline, Option 1 and Option 2.

Option 1 is clearly the preferred option

Example 4: Selecting treatment options

Flow?Odour concentration?

Technique Chemical composition?

Physical characteristic?

Overall suitability

Carbon filter

Chemical scrubbing

Biofiltration

Incineration

Component Assumption

Emission concentration Approx. 20,000 ouE/m3

Flow rate to treatment Approx. 15 Nm3/s

Moisture content Approx. 70% relative humidity

Temperature Up to 100 oC

Chemical components Insoluble organic compounds

Characteristics of odour source

Options appraisal









Options appraisal

Flow?

√

√

√

√

Odour conc?Technique Chemical composition?

Physical composition?

Overall suitability

Carbon filter

Chemical scrubbing

Biofiltration

Incineration


X

√

√

√

Flow?

√

√

√

√



Overall suitability

Carbon filter

Chemical scrubbing

Biofiltration

Incineration








Options appraisal


X

√

√

√

Flow?

√

√

√

√



Overall suitability

Carbon filter √

Chemical scrubbing √

Biofiltration X

Incineration








Options appraisal


X

√

√

√

Flow?

√

√

√

√



Overall suitability

Carbon filter √ X

Chemical scrubbing √ √

Biofiltration X X

Incineration √ √


Emission concentration 20,000 ouE/m3

Flow rate to treatment 30 Nm3/s

Moisture content 70% relative humidity




Options appraisal


X

√

√

√

Flow?

√

√

√

√



Overall suitability

Carbon filter √ X X

Chemical scrubbing √ √

Biofiltration X X X

Incineration √ √ X








Options appraisal

Summary The technical definition of nuisance provides us with a foundation from

which to objectively assess odour impact risk that is independent of regulatory / operator / complainant opinion.

The techniques offer a valuable approach for investigating the cause of nuisance; identifying and evaluating solutions, and defining effective odour management strategies.

Care must be exercised by applying the techniques for legal purposes.

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