The Scentroid SP50 Oxidisation Purger is a revolutionary device designed to provide effective and reliable cleaning solutions for olfactometers, sample bags, PTFE lines, and other equipment that may be contaminated by odours. The SP50 provides a mixture of clean air with oxidization gases such as ozone and hydroxyl to effectively decontaminate sampling Tedlar or Teflon bags, sampling probes, or sampling lines. The mixture is injected, with the desired concentration to allow high levels of decontamination either, remaining contaminants, bacteria or fungus.

The SP50 has been built with safety in mind, the purger has a built in-carbon filter that scrubs and cleans the contaminated air coming from the equipment that is being cleaned such as bags or probes before it is released into the laboratory.

Benefits of Oxidisation

Oxidisation is a powerful tool for decontamination. Ozone has demonstrated its decontamination capabilities vs. formaldehyde for bio-clean rooms, and high neutralizing effects for several pollutants.

Oxidisation Purger Basics of Operation

Mode 1: Continuous Ozone Injection: Used when the user wants a deeper cleaning of sample bags or probes 

• The operator sets the ozone concentration levels
• The unit provides continuous ozone cleaned air for better decontamination 

Mode 2: User Ozone Injection: Used to quickly clean reusable sample bags or probes

• The operator sets the ozone concentration levels
• The unit injects clean air in continuous mode and ozone with the user presses the “inject ozone” button

For more information on the Scentroid Oxidisation Purger, click here!

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The inability or decreased ability to perceive an odour as continued exposure to that odour increases over time.  An odour may initially be strongly detectable but may diminish completely in a few minutes. Hydrogen sulphide is an example of a chemical that emits a rotten egg smell, but depending on concentration and exposure time, the rotten egg smell will no longer be perceived even though it is still present.  Olfactory fatigue is not desired during olfactometry analysis or ambient odour monitoring.  In the “EN13725 standard”, are allowed for a series of measurements during olfactometry analysis.

During ambient odour monitoring, it is desired to provide rest periods in a neutral environment compared to the one odour is present if possible.  An example may include a vehicle, which may act as a separate environment to the one ambient odour monitoring is taking place. Perfumeries use coffee bean odour to ‘reset’ the olfactory sense. Also, having neutral odourless air to be smelled for a few minutes may help reset the olfactory sense.

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Pertaining to the sense of smell. It is the least understood of the five senses.  No device exists that has the ability to measure odour response as the human nose. The process of olfaction essentially involves a molecule that stimulates nerve cells called olfactory cells where this information is sent to the brain for interpretation.

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The process of analyzing the responses of odour(s) using human subjects (assessors). The responses can be used to determine the odour concentration of odour intensities or the hedonic tone of the odour. Assessors will use a series of devices known as olfactometers.

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A device that is used to determine odour concentration, odour intensity and hedonic tone. This is achieved by diluting the odour sample with odour-neutral air, which is then presented to a panel. The dilutions may be done by volume or flow-rate and are referred to as a static olfactometer or dynamic olfactometer respectively.

The device may be a mobile unit or permanently in place. It is important to note that the olfactometer should be in an odour free environment so as to not to interfere with measurements. Materials used in an olfactometer must be an odour neutral substance such as stainless steel or PTFE.

Olfactometer Range

According to the EN13725, the range of an olfactometer shall be less than 2⁷ to at least 2¹⁴, with a range of 2¹³.  The presentation of diluted air (neutral gas and odour sample) is to be at least 20l/min.

A full list of Scentroid olfactometers can be found here.

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American and Australian Odour Unit (OU)

One odour unit is a number where a panel is presented odours in decreasing dilution (increasing concentration) until detection. This is termed the detection threshold (DT) and is 1 Odour Unit.  Above all, if a sample were diluted 500 times, the odour concentration is 500 dilutions / 1 OU of the sample. This would result in 500 OU.  This can be expressed as ‘dilutions to threshold’.  However, the panel can only detect at 1OU (the detection threshold) and not 2OU for example.

European Calculation (OU_E/m³)

One European Odor Unit, [OU_E/m³], is the amount of odourant(s) evaporated into one cubic metre of neutral gas. At standard conditions, it elicits a physiological response from a panel (detection threshold). Above all, This is equivalent to that elicited by one European Reference Odor Mass (EROM), evaporated in 1 m³ of neutral gas. One EROM is equivalent to 123microg n-butanol.  Subjects are standardized to n-butanol which is the reference material.  When odours are detected at the threshold, it is expressed as a multiple of the reference material.

For reference, 1 EROM ≡ 123 µg of n-butanol ≡ 1 OU_E for the mixture of odorants

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A location or object that emanates odours. Sources can be divided by point, area, or volume sources that are of either passive, active or fugitive type. For example, a rectangular oil pond would be labelled as a ‘passive area source’ and a biofilter may be labelled as an ‘active area source.’ The term diffuse source is used to describe area or volume sources. Fugitive samples are essentially unintended releases of odour. A summary is shown below:

Point source > Passive or active or fugitive

Diffuse source  > Area source or volume source  > Passive or active or fugitive

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A measure of how strong an odor may be based on an initial perception. Odor intensities and odour concentration have a non-linear relationship. For instance, if two distinct odours are both at a concentration of 3 OU/m3, the resultant intensity measurement may result in one being more offensive than the other.  For example, a low odour concentration of hydrogen sulphide (rotten egg smell) may have a higher odour intensity due to the nature of the smell.

VDI 3882 Qualitative Scale

The German standard Olfactometry Determination of Odour Intensity VDI 3882 Part 1 outlines a qualitative scale to measure odour intensity shown below:

Unlike measurements of odour concentration that take place at the detection threshold (1 OU/m3), odour intensity measurements are taken at and beyond the detection threshold. Note that the odour concentration is known for each odour intensity measurement since the detection threshold is known a prior and can be adjusted by changing the dilution.

Once odour concentration and intensity are determined, they can be expressed as a nonlinear mathematical relationship.  Intensity increases linearly with the logarithm of the odour concentration.  Some formulae include Weber Fechner Law (exponential function) and Stevens Law (power function). 

Webner Fechner Law (Exponential Function)

Webner Fechner Law is shown below:

I = kw log(C/Co) + const

Where:
I: Odour Intensity
kw: Weber-Fechner constant
C: Odour Concentration;
Co: Concentration of odorant at the detection threshold (by definition equals 1OU when using odour units);
const: a constant which relates to the use of mean intensity levels that can be calculated from the line of best fit for each odorant.

An example calculation can be found in the German Standard VDI 3882 for the Webner Fechner Law.

Steven’s Law (Power Function)

Stevens Law is shown below:

I = k(C)ⁿ

Where:
I represents odour intensity
C:  odour concentration
K: constant
N:  exponent

A straight line in logarithmic coordinates appears if function plotted as:

log I = log K + nlog (C)

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Uses a three-level framework in the assessment for odour sources.

A Level 1 odour impact assessment is a simple screening based on general site activity and parameters. This level requires minimal data and is used to determine the likely extent of an odour. It may be used is in smaller developments and less populated areas or sites with few sensitive receptors.

Level 2 odour impact assessments use a dispersion modelling technique using worst-case scenario data. This level is more in-depth and provides a more realistic prediction of any odour impact than level 1. This level of impact assessment may be used when determining whether an upgrade to a wastewater facility will result in an odour impact.

Level 3 odour impact assessments are is a modelling technique that uses site-specific data and therefore is the most comprehensive impact assessment.

Reference: Assessment and management of odour from stationary sources in NSW.

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Determines the odour concentration per time from a source. It is calculated by taking the product of the odour concentration and flow rate from a source. For example, if a stack has a volumetric flow rate of 2m3/s and the olfactometry analysis resulted in 220 OU_E/m³, then the OER = 2m3/s * 220OU/m3 = 440 OU/s. It is not sufficient to calculate the odour concentration but to determine the rate of odour emission during and evaluation of the source.

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