Sampling and olfactometric analysis: a constant challenge

sesion03 vergara04To ensure the representativeness and quality of the results of olfactometric analysis, it is essential to identify and monitor each of the variables involved in the entire process, including prior, during and after sampling.

Bravo M.J., H. Vergara

Ecometrika - Av.americoVespucci 2296, Conchalí, Santiago, Chile

mjbravo@ecometrika.com , hvergara@ecometrika.com

Competing interests: The author has declared that no competing interests exist.

Academic editor: Carlos N Díaz.

Content quality: This paper has been peer reviewed by at least two reviewers. See scientific committee here

Citation: Bravo M.J., H. Vergara., 2014,Sampling and olfactometric analysis: a constant challenge., Ist International Seminar of Odours in the Environment, Santiago, Chile, www.olores.org

Copyright: 2014 olores.org. open access Creative Commons, It is allowed to download, reuse, reprint, modify, distribute, and/or copy articles in olores.org website, as long as the original authors and source are cited. No permission is required from the authors or the publishers.

Keywords Olfactometry, VDI3880:2011, olfactometricsamples, homogeneity, temperature, analysis time

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Abstract

   To ensure the representativeness and quality of the results of olfactometric analysis, it is essential to identify and monitor each of the variables involved in the entire process, including prior, during and following sampling. Standard VDI 3880:2011 addresses this issue specifically, providing guidelines that allow for controlling and minimising harmful variable effects with respect to the representativeness of the sample both during the sampling as well as the stages prior to the olfactometric analysis. Before sampling, proper planning and detailed knowledge of the process to be characterised become important when performing a representative sampling. The same thing occurs during the sampling, where particular conditions on the ground may be present and should be considered. Finally, after sampling, during the stages of transportation, storage and conservation of the olfactometric samples, it is possible to classify two sets of critical factors that affect odour concentration, upon directly interacting with the sampling bag or indirectly with the sample collected, these being environmental and operational factors. Hence the importance of addressing the variables that may or may not influence a representative sampling and olfactometric analysis, beginning with the initial stages of the process.

 

1. Introduction

Although there are some technical guidelines in the European Standard EN13725:2003 concerning olfactometric sampling, standard VDI 3880:2011specifically addresses points related to a static olfactometric sampling. Among the main variables that are directly related to the sampling and analysis that will be carried out in this document, is the importance of the technical and specific information of the processes to sample as input information for each project's sampling olfactometry. The homogeneity of the surfaces to sample will also be analysed as relevant in achieving representativeness of the selected points. Finally, after sampling, the transportation and storage of the samples will be considered as important variables.

 

2. Theoretical development

2.1 Sampling inputs: planning prior to sampling

This section evaluates the importance of maintaining a smooth, precise and direct communication with the buyer of a service, in relation to the delivery of information and how this is reflected in the first stage of a project: sampling.

Based on the experience of companies of different products (projects), plans for the different types of sampling have been developed, depending on the type of source. However, it is critical to have all of the information attached that could be reflected in the sampling planning. In this way, companies that report being operational 24/7, and operate every day of the year, have a period of "x" hours during the day in their operation where they operate at full capacity.

In the case of an odourant impact study, instances of information delivery prior to the modelling process to determine the odour dispersion and that will directly affect the sampling stage, are reflected with contact or an approach towards the customer which is what allows the generation of the service to deliver: project type, number of sources, number of samples, determination of critical or relevant sources, determination of the sampling schedule (operational status):

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Case study: Determination of Odour Emission Rates (OER) based on operational conditions

In a sampling situation during a process of washing of organic waste from farm animals, the OER must be determined both to characterise emissions by animal raising age, and to determine the scope of the odour by means of an atmospheric dispersion model.

In the initial contact with the customer, the operational condition of the farm – the washing system for the organic waste from animals – had not been considered. Based on this information, we planned the sampling in order to determine the variations in odourant emission rates for different animal raising ages, prior to, during and following the washing process. Having received this information before making a schedule, it became crucial to determine the optimal sampling schedule, data that would later be reflected in the dispersion model.

The following is the result of the waste disposal from the farm, for an initial age of animal raising:

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Fig. 1. Odour Emission Rate chart for sampling time during waste washing

It was determined that the emissions varied during the day as the organic waste was disposed. The greatest emissions range was a period of approximately 12 minutes, where the discharge had commenced, and then decreased minutes after the process had been completed.

2.2 Homogeneity: Condition during sampling

The main variables that define the types and characteristics of sources to sample, is the degree of homogeneity, which is determined for a homogeneous flow of emissions based on the guidelines of the German standard VDI 3880:2011, wherethe speeds of the different sections of the surface to sample differ at most by a factor of 2.

For sampling purposes, the importance of homogeneity lies in considering a surface representative of odour emissions, and thus obtaining a particular characterisation of the source allowing a projection of the emission.

Case study: homogeneity of sources

In general terms, when there are passive sources, in addition to having low odour emission flows, for the most part they do not have significant differences between them, a condition that requires generating a flow forced upon the surface.

In this case, a good tool to confirm the homogeneity of the sample surface is the consideration of the surface temperature of the source, measured by thermographic images.

Homogeneous sources

The condition of a "homogeneous" source will be present when there is a maximum variation of up to 50%, in degrees, for the maximum and minimum temperature with respect to the measured average temperature on the surface.

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 Fig. 2. Comparison of actual and thermal image from an Industrial Waste Water treatment pool

Figure 2 shows an example with actual information from an Industrial Waste Water treatment pool from a rendering industry in which there is surface homogeneity, confirmed by both the thermal imaging as well as the temperature data obtained, as shown in table 1.

Table 1. Characteristics of the source and surface temperatures in the Industrial Waste Water treatment pool

Source:

Industrial Waste Water treatment pools

Type of source

Passive

Type of surface

Liquid

Average temperature of the source

13.7°C

Minimum temperature

13.1°C

Maximum temperature

14.3°C

Δ minimum Tº with respect to the average

0.6°C (-4.4%)

Δ maximum Tº with respect to the average

0.8ºC (+ 5.8%)

Δ: Delta Temperature

For the planning of sampling in such sources, simple or composite samples can be considered due to the homogeneous condition of emission.

Non-homogeneous sources

A given source is considered non-homogeneous source when there is a difference or variability in emission flow at different points by a factor greater than 2, a condition that is measurable by the field sampling staff, however, there are some particular conditions in which there may be sources that meet this condition in terms of flows, and upon evaluatingthe surface emission and its temperature, conditions of heterogeneity may occur that can directly influence the odourant flow to be calculated.

Figure 3 shows the aforementioned situation for the case of a container of animal entrails which shows the presence of hot and cold spots, revealing the heterogeneity of the source.

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Fig. 3. Comparison of actual thermal image of an entrails container
 Table 2. Characteristics of the source and surface temperatures in an entrails container

Source:

Entrails container

Type of source

Passive

Type of surface

Solid

Average temperature of the source

8.7°C

Minimum temperature

4.2°C

Maximum temperature

13.7°C

Δ minimum Tº with respect to the average

4.5°C (-51.7%)

Δ maximum Tº with respect to the average

5.0°C (+ 54.0%)

Δ: Delta Temperature

For the planning of sampling for such sources, if considered a simple sampling, it is important to define a large number of simple or composite samples that allow the inclusion of the various points of emission from the surface, whether due to variations in flows and/or cold/hot spots.

2.3 Transportation and storage of samples: temperature is key

In accordance with the German VDI 3880:2011, the transportation and storage of the samples must meet certain parameters that are relevant to avoid changes in the odour concentration, in this particular case, for instance: storage temperature below 25°C.

A correlation between the diffusion coefficient of the film and the temperature during the transportation and storage of samples has been observed (Guillot and Beghi, 1998).

For this reason the temperature control during the stages of storage and conservation, acquires great importance, and even more so in compounds that are less stable, such as some volatile compounds.It has been shown that the percentage of sample loss in volatile sulphur compounds doubles over 30°C in comparison with a range between 5°C and 20°C (Le et al, 2013).

The technical standard highlights that to minimise alterations of the samples, the conservation conditions must be ensured above the dew point and not greater than 25°C, thus avoiding situations of condensation inside the bag.

Case: Temperatures of transportation and storage of samples

Ecometrikafrequently performs comparative time studies. One of these tests was carried out to assess the effects that temperature has on the odour concentration in olfactometry samples, The Ecometrika dynamic olfactometry laboratory conducted a laboratory test which compared samples from the same odour emission source, sampled under identical conditions, both analysed immediately following the sampling, and then both samples were stored in different temperature conditions: M1 samples at a controlled temperature of 20°C in an air conditioned container to maintain a stable temperature and a continuous temperature sensor, and M2 samples stored at room temperature during the summer, at an average temperature of 30°C.

All samples were analysed on time at 0600 and 2400 and the results were as follows:

Table 3. Time of analysis, odour concentration and percentage reduction for M1 and M2

Analysis time (hr)

? M1 - Odour Concentration (ouE/m3)

? M2 - Odour Concentration (ouE/m3)

% Variation of Odour Concentration M1

% Variation of Odour Concentration M2

0

5,230

5,180

-

-

6

4,950

4,120

-5

-20

24

4,350

3,020

-17

-42

 

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 Fig. 4. Graphic variation in odour concentration with regard to time and storage temperature

2.4 Storage of samples prior to olfactometric analysis

There are critical environmental factors such as: solar radiation, relative humidity and external or surface contamination in sampling bags. It has been shown that direct exposure of the collected samples to sunlight can promote chemical photoreactions with some components of the sample, affecting their stability and therefore the representativeness of the sample (Tattileet, 2012).

Humidity, both in the storage and conservation of samples, can lead to the rapid spread of some gaseous compounds through the film of the sampling bags affecting results during their analysis (Guillot and Beghi, 1998).

Studies have shown that the sampling bag is a physical barrier for containment of the sample and provides insulation against external agents. The efficiency of the sampling bag depends proportionally on its thickness and composition because there is a significant diffusion coefficient against some compound odourants, especially if they are water soluble as NH3, H2S y CH2O (Hudson and Ayoko, 2008).

On the other hand, direct contact of the film with odourant compounds may alter the actual composition of the sample by chemical adsorption processes.

The critical operational factors that can affect the representativeness of the results correspond mainly to conditions of thermal variability outside the range established by technical standards VDI 3880:2011, the time spent in sampling and in the different stages, prior to the olfactometric analysis of the samples.

Time management in the phases after sampling is crucial to ensure a representative analysis. For this reason, time between sample collection and analysis must be minimised to prevent alterations in the composition of the sample during storage and conservation.

All technical standards to date include maximum time recommendations in their guidelines: 3880 VDI: 2011 - 6 hours, NCh 3190:2010 - 24 hours, in 13725:2003 - 30 hours, various studies have shown the importance of these timeframes, evaluating how the concentration of these samples decreases at different times.

Case study: Variation of the odour concentration according to time of analysis (after sampling).

In order to evaluate the variability in the odour concentration on the elapsed time from the drawing of the sample to the olfactometric analysis, lab tests were performed for sludge and compost samples from a single treatment plant. The experimental conditions were standardised according to the requirements of the technical standard VDI 3880:2011.

The odour concentration in time was established as the dependent variable, the analysis of samples at 0, 6, 24, 30 and 48 hours, whose periods were set based on the time limits established in the regulations VDI 3880:2011:2011, NCh 3190:2010 and on 13725:2003.

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 Fig. 5. Graph of variation in odour concentration with respect to time and storage temperature

Correlation tests were conducted in each period of time to establish the degree of relationship of the series of samples for the same class. The minimum and maximum correlation coefficients observed correspond to: 0.964 and 0.99 for sludge; and 0.930 and 0.990 for compost. At the same time non-parametric statistical tests Kruskal-Wallis were carried out, recording values of 0.226 for sludge and 0.330 for compost on a significance level of α = 0.05. This verifies that the analysed data sets correspond to a same group, validating the results that are presented below.

 

Table 4. Analysis time and odour concentration samples of sludge and compost

Time of Analysis from sampling (hr)

M1 (ouE/m3)

% Variation

M2 (ouE/m3)

% Variation

0

2,366

-

2,656

-

6

645

-73

1,183

-56

24

304

-87

395

-85

30

228

-90

332

-88

48

215

-91

443

-83

The obtained results are congruent with previously published studies.

3. Conclusions

Related to the stages prior to the implementation of a sampling, it is of vital importance to note that the quality of the results will depend on how well the sampling is performed, among other elements, deliveringinput data to dispersion models. One of the items that must be considered in all planning, therefore, is the quality of the information that must be representative of the operating conditions.

In relation to the sampling, it is of great importance for the planning of a representative sampling, to consider the type of source to be sampled and the homogeneity of the sample surface. This will ensure reliable results for the calculation of Odour Emission Rates from sampled sources.

For testing, both forthe storage temperature of samples as well as the time between sampling and laboratory analysis, the results confirm the importance of analysis within the initial hours following sampling and of maintaining a proper and controlled chain of temperature for sample transportation and storage. For this reason, when planning samples where the analysis within that time period may be difficult, proximity to the point of analysis becomes of utmost importance, as well as proper coordination of air transportation and the application of new technologies such as mobile laboratories, which can allow the production of actual results.

4. References

Belgiorno V., Naddeo V., Zarra T. 2012. Odour Impact Assessment Handbook.John Wiley & Sons.

Boeker, P., Haas, T., Diekmann, B., Schulze Lammers, P. 2010. New odour sampling method: adsorption and reconstitution of odours.

EN 13725:2003. 2003. Air Quality – Determination of odour concentration by dynamic olfactometry.

Frenchen, F.B. 2008. Odour Sampling – International Conference on Environmental Odour Monitoring and Control. http://hrzvm162.hrz.uniassel.de/web/SiwawiDokumente/pdf/publikationen/vortraege/2008/G_NOSE2008_Keynote_Rom_2008-07-08_P_SD.pdf

Guillot J, Beghi S. 2008. Permeability to water vapour and hydrogen sulphide of some sampling bags recommended by EN 13725.Ecole des Mines Alès.

Hudson N, Ayoko G. 2008. Odour Sampling 1: Physical Chemistry Considerations. Bioresource Technology Vol.10.

Qu. G., Feddes J. 2013. Estimation of measurable error caused by background odor in sampling bags.American Society of Agricultural and Biological Engineers. PN: 064141

Le H , Sivret E.C.,Parcsi G., Stuetz R.M. 2013. Stability of volatile sulfur compounds (VSCs) in sampling bags - impact of temperature. Water Science & Technology.

Le H.; Sivret E. C.; Parcsi G.; Stuetz R. M. 2013. Stability of Volatile Sulfur Compounds (VSCs) in sampling bags - impact of temperature.WaterScience&Technology. Vol. 68 Issue 8.

NCh 3190:2010. 2010. Calidad el Aire – Determinación de la concentración de olor por olfatometría dinámica.

Richter, C.J., Frenchen, F.B., 2009. Sampling for Olfactometric Measurement: The New VDI guideline 3880.

VDI 3880:2009. 2009. Olfaktometrie – StatischeProbenahme. Draft, Berlin.

VDI 3880:2011. 2011. Olfactometry – Static Sampling. Berlin

 

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