Content

Costs and odour emissions reduction in WWTPs by means of CFD models

There are many cases in which the atmosphere contained into the process buildings on a Waste Water Treatment Plant (WWTP), show important deficiencies regarding air renovation.

R. Cerdá Ortiz *; J.M. Juárez-Galán; A.J. Amo Peña; I. Valor

Aqualogy Medio Ambiente. C/Dracma 16-18. Polígono Industrial Las Atalayas. 03114 Alicante. * ruben.cerda@labaqua.com

Keywords: CFD, odours, ventilation, energy efficiency, WWTP.

Abstract

   There are many cases in which the atmosphere contained into the process buildings on a Waste Water Treatment Plant (WWTP), show important deficiencies regarding air renovation. This contributes to increase the concentration of chemical compounds, which can be potentially responsible of odour episodes, health risk for the operators, corrosion and fugitive emissions. In many occasions, ventilation systems are designed based on over sizing the air changes per hour ratio (ACH), without ensuring an optimal behavior. The verification of ventilation systems efficiency is a very complex task in which the consideration of several parameters is required. Thus, it is mandatory to use tools able to predict the bahaviour of air and pollutans contained into process buildings. Simulation by CFD (Computational Fluid Dynamics) software, is a cutting-edge tool for assisting in the optimization of ventilation systems in process buildings, in a cost and time saving way, with the aim of improving the indoor air quality and the extraction of odours for an adequate treatment, optimizing the costs derived from the ventilation. In this paper, the CFD optimization of the ventilation systems of a sludge dewatering building located on a WWTP is presented. The results of the study show the deficiencies on the initial design proposed so, several modifications, both geometric and operational, were suggested. The study also proves that the most efficient design is not always the one in which the highest ACH ratio is used. The obtained result implies a better indoor atmosphere (lower pollutant concentration), and an approximated cost savings around 25% of the ventilation costs.

 

 

 

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Events

Odours in the Environment, a different kind of conference organised by the Association of German Engineers VDI.

Carlos N Díaz¹

 

¹. MSc Chemistry. University of Seville. Chief Editor of olores.org

  The conference about Odours in the environment organized by the German Association of Engineers (VDI) took place the 29th and 30th of November 2011. In this paper, the articles presented in this conference will be summarised with the aim of filling the gap of information for non-German speakers who did not assist to this conference.

Funding: This work was partially funded by Labaqua S.A.

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

Citation: Díaz, C  (2012) Odours in the Environment (Gerüche in der Umwelt), a different kind of conference organised by the Association of German Engineers VDI. www.olores.org.

Copyright: 2012 olores.org. open access Creative Commons, It is allowed to download, reuse, reprint, modify, distribute, and/or copy articles in olores.org website, so long as the original authors and source are cited. No permission is required from the authors or the publishers.

Key Words: Odours, legislation, VDI conference, dynamic olfactometry.

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In this fourth conference edition the programme has been divided into several parts:

• Immision evaluation
• Sample collection and measurement through olfactometry
• Accreditation of odour consultancy companies
• Prognosis of odours
• Interpretation of odours
• Case studies and projects.

The attendance to the conference was excellent, considering that the conference on odours in Brazil organised by the IWA had taken place only one month prior. In general, the quality of the presentations was satisfactory, even though in this edition some multidisciplinary essays and basic research were missed.

Basic research was the topic of the first presentation, titled “Olfactory receptors in biosensor systems for the detection of odorants”. This interesting presentation was given by Dr. Dietmar Krautwurst, Director of the German Research Institute for Food Chemistry.

Dr. Krautwurst discussed research related to the sense of smell, specifically regarding the discriminatory abilities of humans to recognise a set number of odorant substances, principally through the large family of 391 odour receptors. These receptors together with g proteins have a structure similar to that of Rhodopsin. However, the most important challenge in the coding of odours is finding out which receptor is related to which odorant substance. This question remains unanswered to date for the majority of human odour receptors, 20 years after the discovery of Nobel Prize winners Buck and Axel.

It is known that a receptor can be activated in principle through different odorous substances, and at the same time one odorant can activate multiple receptors. The challenge of delineating these different combinations is enormous, especially considering – for example – that only 200 of the approximately 8,000 volatile substances that can be found in food are biologically important odorous substances. Molecular biology and genetics have joined together to create cellular test systems that allow the clarification of the specificity for each fragrant substance in relation to each type of odour receptor. Through these cellular test systems, congruent classifications can be established based on the level of affinity of each receptor and its specificity for each odorous substance.

ODOUR ASSESSMENT ON AMBIENT AIR

 

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The part of the VDI conference’s programme dedicated to immision evaluation was moderated by Dr. Eckehard Koch, Chief of the Department of Atmospheric Pollution of the Ministry of Climate, Environment, Agriculture, Natural Protection and Consumer Protection of North Rhine-Westphalia, Düsseldorf. Mr. Koch is well known in the world of odours and has broad experience in the field.

The first presentation in this section titled the New European Directive on the Assessment of Odour Immision levels with the Plume and Grid measurement methods was presented in equal parts by Mr. Werner- Jürgen Kost, who presented the section on VDI 3940 and Mr. Toon van Elst, who presented the section on the guidelines corresponding to Belgian regulations.

Work group 27 (WG 27) of the European Guideline CEN /TC 2641WG27 “air quality” technical committee has been working for several years on a European guideline for the evaluation of odour immision with field inspections. In this international work group (28 participants from 13 countries) the different methods of estimating used in Europe will be brought together, in addition to any other updated information available, with the objective of elaborating the broadest and most uniform  European guideline possible.

Due to differences in their respective objectives and evaluation frameworks, each country has applied different estimation methods. In this case, the European Guideline will be divided into 2 parts. In part 1 the procedure of the “grid” measurement will be described and in part 2 the procedure for the “plume” measurement will be elaborated. Within Part 2, 2 different methods will be described: the static plume measurement and the dynamic plume measurement.

This European Guideline is the direct consequence of work developed over the course of almost 30 years with the German guideline VDI 3940.  

The second presentation was given by Mr. Zimmerman, project chief at the Department of Environment in the Müller-BBM GmbH Company. This presentation discussed the influence of the choice of planned inspection date on the results of the evaluation areas in field inspections using the grid method.

An important component that will allow the evaluation of the validity of an immision measurement is knowledge of its capacities and constraints. During an odour inspection this can be crucial if the result is close to the limit established by current regulations. In the case of odour impact studies utilizing the grid method, the result of the measurement is affected by an uncertainty that depends on the number of measurements taken. In other words, the result depends on the statistical estimation method chosen.

Mr. Zimmerman presented research showing the results of 3 field inspections carried out according to the VDI 3940 with the grid method. The purpose was to examine how the result would vary if the measurement dates were changed in each one of the vertexes in the estimation area.

In this interesting and exhaustive research, 24 possible combinations of panellist distributions were carried out for a measurement square.

• In the same period of time
• With the same distribution (for example on the same days during the same time period of the year)
• The same group of panellists ⁽¹⁾
• The same panellist for each measurement day
• Approximately the same time of measurement for each point

But with a variation in the estimation days for individual measurement points.

The Standard Deviation and confidence interval data for the measurement results show that the uncertainty in the method probably has a greater influence on the measurement result than the uncertainty related to the measurement itself. In other words, in this interesting research significant variations have been found depending on the choice of dates for field inspection.

SAMPLE COLLECTION AND MEASUREMENT WITH OLFACTOMETRY

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The part of the VDI conference programme dedicated to sample collection and measurement with dynamic olfactometry was moderated by Mr. Dietmar Mannebeck.

The first presentation in this second section titled “Proficiency testing trials according to Guideline EN 13725 in 2010” was presented by Mr. Bjorn Maxeiner, Director of Odournet GmbH (previously OLFAtec GMBH).

Determining the odour concentration with dynamic olfactometry is an internationally recognised measurement method which is described in guideline EN 13725 “Air Quality. Determining odour concentration with dynamic olfactometry”. Since 2003 the OLFAtec Company has been carrying out proficiency testing for dynamic olfactometry. The principal objective of these tests is to verify accuracy and precision based on the requirements specified in Guideline UNE EN 13725 and the guidelines ISO 5725-2:1994 e ISO 13528:2005, among others.

In the aptitude test carried out in 2010, 37 testing laboratories from around the world participated, of which three laboratories were Spanish and one was Chilean. Since ENAC’s website (Spain) lists 4 testing laboratories accredited in Spain, one can deduce that there is at least one that has not participated in the proficiency tests in Spain.

On this occasion work began again on a decentralised test in which an independent observer was assigned to work as a monitor of the test. Noteworthy beginning in 2010, laboratories were given the option to choose an external coding institute to apply a double blind test (this requirement will be obligatory as of 2012). This external institute ensured that the data were anonymous for participants as well as for organisers.

Also noteworthy for 2010 was the possibility of demonstrating precision (like repeatability) and accuracy of the laboratory trials with a gas other than n-butanol. The gas chosen was a combination of DMS/TBM (Dimethyl Sulfide/Tertiary Butyl Mercaptan).

The following chart shows for example the precision (r) and accuracy (A) data in the case of n-butanol gas for the different laboratories that participated in the proficiency tests calculated according to EN 13725 and ordered by precision value. Let us remember that the guideline establishes the following limits: r = 0.477 and A = 0.217.

Chart 1: Precision r and accuracy A for n-butanol according to EN 13725. Reproduced with permission from Mr. B. Maxeiner, 2011, VDI Gerüche in der Umwelt.

Unfortunately, not all the labs participating in a proficiency test publish their individual performance results in their website. this is a way to check the transparency of a testing laboratory. At Olores.org we encourage to every laboratory participating in a PT to publish their results in their websites.

The conclusions of the research from Mr. Maxeiner were the following:

• The use of an aptitude test is appropriate to be in compliance with the essential requirements for the Standard EN 13725.
• The requirements are challenging, but within reach.
• As of 2012 it will be obligatory to use the services of a coding entity.
• Also in the future other odorous substances like the DMS/TBM combination will be offered along with n-butanol.

The second presentation from this section was given by Mr. Ralf Both, Advisor to the Regional Office of the Environment and Consumer Protection of North Rhine Wesphalia, Recklinghausen. Currently, Mr. Both is posted in Seville in the Institute for Prospective Studies (IPTS) of the Joint Research Centre (JRC). His conference was titled “Reflections on uncertainty in olfactometric measurements. An evaluation of the n-butanol data from 19 laboratories.”

The evaluation of uncertainty in measurement plays an important role in evaluating the quality of some measurements. Determining the uncertainty in olfactometric methods is difficult even for a single measurement. Carrying out 2 measurements to improve this calculation implies a great effort for laboratories. According to Mr. Both, there is currently no adequate proficiency test offered, and the use of sample replicas is so infeasible that that another measurement system is needed.

The estimation of uncertainty with olfactometric methods is based on the estimate of precision as repeatability (r) and accuracy (A) according to guideline EN 13725, but this does not provide an estimate for the real measurement uncertainty according to the ISO 20988 Air Quality. Guidelines for the estimate of measurement uncertainty or the German guideline VDI 4219 determining the uncertainty of measurements in emissions with discontinuous methods.

In the research presented by Mr. Both the results of the precision and accuracy data were analysed from 19 olfactometric laboratories with samples of n-butanol according to guideline EN 13725. Based on this data the Factor 10^r of each one of the laboratories was calculated and the results were compared.

With the exception of one case in which the laboratory reported an r above the limit established by EN 13725 (> 0.477) in the worst case one laboratory reported a result of r = 0.4432 (10^r = 2.8). The laboratory that obtained the best result reported a precision r of r = 0.1424 (10^r = 1.4).

This means that even though all of the laboratories considered met the criteria established in EN 13725, the difference between the results of the two individual measurements taken by the best and the worst laboratories evaluated in the same sample, in 95% of cases could vary by a factor of 1.4 and 2.8 respectively.

 

Lab Date Accuracy A Repeatability r Number  Individual Odour Estimated ZITE Lab_01 19-11-07 0.0828 0.2065 11 Lab_02 01-02-08 0.0648 0.3464 115 Lab_03 20-12-06 0.1271 0.4880 55 Lab_04 29-04-08 0.1093 0.3434 10 Lab_05 23-01-08 0.1661 0.3963 85 Lab_06 19-03-08 0.0988 0.3875 54 Lab_07 12-11-07 0.1485 0.2694 75 Lab_08 16-05-07 0.0920 0.3716 132 Lab_09 20-02-08 0.2396 0.3778 35 Lab_10 07-02-08 0.1787 0.1995 152 Lab_11 16-04-08 0.1098 0.3379 12 Lab_12 14-01-08 0.1108 0.2046 48 Lab_13 20-02-08 0.0579 0.3444 54 Lab_14 13-02-08 0.0370 0.2317 37 Lab_15 19-03-08 0.1701 0.3561 330 Lab_16 12-09-07 0.0938 0.3311 697 Lab_17 19-02-08 0.0955 0.4432 77 Lab_18 07-04-08 0.0905 0.3890 162 Lab_19 13-02-08 0.1357 0.1424 10

Table 1: Precision (r) and accuracy (A) for 19 laboratories. Reproduced with permission of the author. Both, R.; Müller, F. (2011): Überlegungen zur Messunsicherheit bei olfaktometrischen Messungen – Eine Auswertung der n-Butanol-Daten von 19 Laboratorien. In: VDI Wissensforum GmbH (Hrsg.): Gerüche in der Umwelt. VDI-Berichte 2141, S. 43–54

Using, for example, a result of 532 ou_E/m³ Mr. Both reflected on the upper and lower values with a confidence interval of 95% for each laboratory.

Chart 2: Precision (r) of a supposed measurement of 532 ouE/m3 from each testing laboratory for a confidence interval of 95%. Reproduced with the permission of the author. Both, R.; Müller, F. (2011): Überlegungen zur Messunsicherheit bei olfaktometrischen Messungen – Eine Auswertung der n-Butanol-Daten von 19 Laboratorien. In: VDI Wissensforum GmbH (Hrsg.): Gerüche in der Umwelt. VDI-Berichte 2141, S. 43–54

Using the calculation methodology of guideline VDI 4219, an estimate of the standard uncertainty u(y) and the expanded uncertainty U_0.95(y) was made for each one of the 19 laboratories. In order to do this, 3 situations were studied with the n-butanol data available from these 19 German laboratories.
 

1.    Random selection of all of the values measured by each testing laboratory.

In order to do this 40 n-butanol measurement results from each one of the 19 laboratories were taken and chosen at random. Based on these results 20 value pairs were generated, with which an analysis of uncertainty was carried out according to German guideline VDI 4219. The standard uncertainty u(y) varied between 3.4 and 16.3 ppb and the U_0.95(y) varied between 7.1 and 33.9 ppb. Nevertheless, the most interesting part of this exercise of analysis was that for 7 laboratories, the lower limit of the application range was below the value of the expanded uncertainty. In other words, the application of this expanded uncertainty for n-butanol for these 7 testing laboratories would generate threshold odour values below 0 ppb, which is impossible!

For this reason, the focus on the calculation of measurement uncertainty based on the estimate of uncertainty in concentrations of n-butanol is not adequate.

Mr. Both continued with another series of examples that demonstrated that the use of VDI 4219 for the calculation of olfactometric measurement uncertainty is not possible, such as:

2.    Use of the most current methods in each testing laboratory.

The standard and expanded uncertainty was calculated for the 20 most updated measurement pairs of each laboratory, generating the same result: for 7 laboratories the lower limit value of the application range was less than the expanded uncertainty. As previously mentioned this is not possible, the odour threshold can never be less than or equal to zero.

3.    Use of a series of measurements with identical test gas concentrations.

Of all of the measurement series from each testing laboratory, 40 were chosen that carried out the same test concentrations of gas. Of the results of these 40 measurement series, 20 measurement pairs were established, to which an uncertainty analysis was performed again. The results matched previous analyses.

  With the three previous analyses, the conclusion is drawn that using a linear scale for the evaluation of measurement uncertainty does not offer plausible results and therefore a different approach is needed.

Estimate of expanded uncertainty U_0.95(y) of repeated measurements.

Mr. Both calculated the mean value and the expanded uncertainty for a confidence interval of 95% for the 10-20 latest estimates of the odour threshold for n-butanol reported by each laboratory. For the determination of the uncertainty MU, the mean values y_m were used on a logarithmic scale and later the sum of the averages plus the logarithmic expanded uncertainty was determined (y_m+ U_0.95(y)).

The average of the uncertainties MU of all of the laboratories produced a value of 1.8 dB_od(odour decibels)⁽²⁾.

 

Laboratory ym (linear) [ppb] U0.95(y) (linear) [ppb] Level of ym [dBod] Level of ym+U0.95(y) [dBod] Level of MU [dBod] Lab_01 36.6 5.19 15.6 16.7 1.1 Lab_02 40.9 10.88 16.1 18.0 1.9 Lab_03 35.7 12.95 15.5 17.9 2.4 Lab_04 43.1 11.04 16.3 18.1 1.8 Lab_05 50.5 16.86 17.1 19.3 2.2 Lab_06 36.7 12.91 15.6 18.0 2.3 Lab_07 51.0 10.25 17.1 18.5 1.5 Lab_08 37.1 11.35 15.7 17.8 2.1 Lab_09 26.4 7.58 14.2 16.2 2.0 Lab_10 56.1 8.58 17.5 18.7 1.2 Lab_11 36.4 9.46 15.6 17.4 1.8 Lab_12 33.4 4.98 15.2 16.4 1.1 Lab_13 39.7 8.97 16.0 17.6 1.6 Lab_14 40.0 7.70 16.0 17.4 1.4 Lab_15 30.8 8.47 14.9 16.8 1.9 Lab_16 44.0 12.00 16.4 18.3 1.9 Lab_17 37.7 15.90 15.8 18.4 2.7 Lab_18 42.8 12.67 16.3 18.3 2.0 Lab_19 50.8 5.08 17.1 17.9 0.8

Table 2: Measurement results of the repeated measurements (odor level). Reproduced with permission of the author. Both, R.; Müller, F. (2011): Überlegungen zur Messunsicherheit bei olfaktometrischen Messungen – Eine Auswertung der n-Butanol-Daten von 19 Laboratorien. In: VDI Wissensforum GmbH (Hrsg.): Gerüche in der Umwelt. VDI-Berichte 2141, S. 43–54

A similar exercise was carried out by taking an odour concentration sample of 532 ou_E/m³ (≈ 27.3 dB_od) and observing the lower and upper values generated based on the uncertainty calculated. The results of this analysis are shown in the following table.

Laboratory   Level of MU (dBod) Measurement result (dBod) lower limit (ouE/m3) Measurement result (ouE/m3) upper limit (ouE/m3) Lab_01 1.1 27.3 413 532 685 Lab_02 1.9 27.3 343 532 824 Lab_03 2.4 27.3 306 532 925 Lab_04 1.8 27.3 351 532 805 Lab_05 2.2 27.3 321 532 883 Lab_06 2.3 27.3 313 532 903 Lab_07 1.5 27.3 377 532 751 Lab_08 2.1 27.3 328 532 863 Lab_09 2 27.3 336 532 843 Lab_10 1.2 27.3 404 532 701 Lab_11 1.8 27.3 351 532 805 Lab_12 1.1 27.3 413 532 685 Lab_13 1.6 27.3 368 532 769 Lab_14 1.4 27.3 385 532 734 Lab_15 1.9 27.3 343 532 824 Lab_16 1.9 27.3 343 532 824 Lab_17 2.7 27.3 286 532 991 Lab_18 2 27.3 336 532 843 Lab_19 0.8 27.3 442 532 640

Table 3: 95% confidence interval, depending on the level of uncertainty. Reproduced with permission of the author. Both, R.; Müller, F. (2011): Überlegungen zur Messunsicherheit bei olfaktometrischen Messungen – Eine Auswertung der n-Butanol-Daten von 19 Laboratorien. In: VDI Wissensforum GmbH (Hrsg.): Gerüche in der Umwelt. VDI-Berichte 2141, S. 43–54

The analysis was later repeated with an odour concentration of 1000 ou_E/m³ (30 dB_od). All these results show that the calculated values have a plausible magnitude, that makes valid this method for estimation of the uncertainty of the measurement. The implied transferability to odours in the environment can be calculated using the level of the expanded uncertainty on the basis of the data of n-butanol from a laboratory with this method. In addition, the levels for the lower and the upper limits in a lineal scala can be estimated.

In the next presentation, given by Mr. Claus-Jürgen Richter, Director of iMA Richter & Röckle GmbH & Co. KG in Freiburg, the principal new features were given of the new guideline VDI 3880, Static sample collection in olfactometry recently published in October of last year.

The new guideline VDI 3880, contains the following chapters:

1. Planning sampling and measurement

2. General requirements for sampling

• Work conditions
• Sampling team
• Sampling bag
• Implementing sample collection
• Predilution
• Sampling time
• Number of samples
• Sample storage
• Sample transportation

3. Performance of sampling by the type of source

• Active sources
• Passive sources (ex. diffuse sources)

4. Quality Assurance

A general description of the contents of each chapter will be now discussed.

1. Planning sampling and measurement

For the planning of measurement a deep knowledge of plant processes will be necessary. It will be necessary to understand the processes that are carried out, the production of the plant, as well as emission flows. Planning will also require looking into the possible composition of gas that is going to be analysed, as the protection of the panellists is the main priority.

2. General requirements for sampling and analysis

2.1 Sampling duration

The sampling period will generally be half an hour. Only in special cases will some specific exceptions be made, since the operating processes prevent sample collection during this time. In this case, this must be duly justified in the measurement report. The flow of extraction from the sampling system must be designed in such a way that even the smallest volumes can be collected.

2.2 Number of samples

If the results of the measurements are going to be used later in an odour dispersion model, a representative distribution of the situation of the plant must be recorded if possible. As the relevance of an odour source depends on the odour flow as well on its duration, at least three samples for each “normal condition” of operation must be taken, regardless of the levels of emission and duration.

In case the measurement results are to be used to certify the compliance with a limit value, the number of samples to be taken and the manner of taking them will depend on whether the plant functions normally in stable conditions or if the process is variable.

In the plants that function under stable working conditions, without significant variations, at least 3 individual measurements must be taken in continuous operation with the odour flow established at maximum load conditions and at least one additional measurement under normal conditions of operation.

In plants whose industrial processes are variable over time, samples at least must be taken during the 6 different conditions of operation that are believed to be responsible for the higher rates of odour emissions.

2.3 Average

The geometric mean (not the arithmetic) of the concentration measurements and the odour flows.

2.4 Storing of the odour samples

The analysis of olfactometry must take place in the shortest possible time period after the collection of the sample to minimise the possible changes in the samples during their storage. The maximum storage time must not exceed six hours. This represents a significant shortening in the time of analysis for a sample with respect to the requirements of guideline EN 13725 that sets a maximum of 30 hours. During the transportation and the storage, the temperature in the sample bags should not rise above 25 ° C.

3 Sample collections at point, source and volumetric surfaces

3.1 Distinction between active and passive sources

The emission of odours takes place in the interface between the odour source and the open air. For this reason, different sample collection methods will be necessary depending on the nature of this interface.

For fixed sources (chimneys and other emitting sources) the emission of odour will depend to a great extent on the flow of the odour emitted into the atmosphere. Therefore, during the measurement of a cross-section of the flow the higher volumes and odour concentrations can be recorded. In this way the mass flow of the emissions in odour units by unit in time can be calculated through a simple multiplication.

It does not matter if the interface is liquid-air (ex. waste water, slurry) or solid-air (ex. waste, compost), the odours can be transmitted by diffusion as well as by convection through the material (ex. bio-filters, ventilated tanks). If the velocity of the release of odourous gases is much greater than the velocity of atmospheric diffusion, the source will be named an “active source”. Otherwise it will be considered a “passive source”.

According to the theory of the boundary layer, the rate of diffusion is limited by the resistance of the laminar sublayer. The laminar sublayer is typically only a few milimeters thick but it can be up to 10 mm thick. For this reason, the rate of diffusion can vary from a few milimeters per second to up to 10 meters per hour. In comparison, in bio-filters the flow generally varies between 50 m/h and 250 m/h.

In guideline VDI 3880, the boundary between an active and a passive source is established by agreement at 30 m³/(m²•h).

3.2 Active point sources

Active point sources are for example ventilation tubes or chimneys. The sampling method for these sources is described with sufficient precision in the guidelines UNE EN 13725 y UNE EN 15259. The VDI 3880 refers to these guidelines for simple collection in these types of sources.

3.3 Active surface sources

Active surface (or ventilated) sources are for example the open bio-filters or other ventilated surfaces that have a flow above 30 m³/(m²•h). If the flow is lower the odour emission source should be dealt with as a passive source.

For active sources it is possible to determine the odour concentration in basically two ways:

1. Total covering of the source or
2. Selective sampling in different sub-areas.  

 

The total covering is preferable to the selective sampling method as long as the surface area is small enough to make the covering viable. The total covering has an advantage in that all of the odour flow exits through one opening and therefore determining the total intensity of the source is possible with only a few samples. Likewise the mean value of the odour concentration and the total odour flow can be determined with certainty.

In practice, a polythene sheet can be used with a thickness between 0.10 mm and 0.15 mm, such as for example the sheet that is used for silage in agriculture. Regardless the material of the covering should have little odour itself.

The sheet should be placed in such a way that other emissions from peripheral areas are not permitted to enter the emissions source. The placement device for the sheet should be strong enough to allow the full inflation of the sheet. Once the sheet is inflated, it must not touch the surface of the filter. In VDI 3880 additional specifications can be found for the total covering of a source.

Selective sampling in certain parts of the emissions area has the advantage of allowing the distribution of the flows from a surface source to be known; for example, this can be used to ascertain the state of an open bio-filter. In general, the pyramid shaped bell that covers a surface area of 1 m² should be used. In VDI 3880 additional specifications can be found for this device. The VDI-3880 likewise provides orientation on the number of sampling points, the size of the sampling sub-areas and the methods of evaluation.

3.4 Passive Surface Sources

Passive surface sources are those whose volumetric flow per surface unit is less than 30 m³/(m²•h). Examples of this type of surface are rubbish dumps, decanters of Waste Water Treatment Plants (WWTPs), compost piles, manholes, ventilated or non-ventilated biological tanks, etc.

For these types of surfaces a notable influence over the velocity of diffusion in the emission flow total is expected and a device that covers the defined area will be necessary, through which a current of odour-free air will move at a known flow rate. The design details of this device are discussed in detail in guideline VDI 3880.

The number of measuring points on a passive surface will depend on the size and homogeneity of this source, for example, for a 100 m² homogenous passive source, at least 3 samples in three different points on the surface should be taken. For non-homogenous surface sources (for example rubbish dumps) the number of samples must be greater.

3.5 Passive volumetric sources

Passive volumetric sources consist of a horizontal plane as well as a vertical one whose length cannot be insignificant. This type of source generally includes entire buildings where odours are emitted through windows, doors, ventilation shafts on the roof, etc. situated at different heights.  

These types of sources can be measured with adequate planning. Nevertheless, in more complex cases, for example in refineries, this method is not adequate and another method must be used to measure protection distances based on plume dispersión through guideline VDI 3940 part 2.

The flow rate of a non-ventilated building can be calculated based on the air exchange rate per time unit. With the product of the flow rate and the volume of the building the diffuse emission flow can be generated.

Since the flow in the interior of a building is not always uniform, the preferred pathways of the flow should be taken into consideration. An adequate method can be the use of a gas tracer such as hexafluoride Sulfur SF6 or carbon dioxide (CO₂). In this case the number of air changes per hour can be calculated with the decay method. This method is described in detail in the guideline.

The key points of the new VDI 3880 are the following:

1. A sampling period of half an hour is established.
2. The storage time for the samples prior to analysis is limited to 6 hours.
3. Sample collection in passive sources is described in detail.
4. Predilution methods are described in detail.

The next presentation in the programme was given by Mr. Frechen, Chief of the Department of the Urban Management of Water and of the Institute for Water, Waste and Environment from the University of Kassel. This presentation was postponed until the end because the speaker was unable to participate in the first part of the conference. However, as this is part of the sampling and olfactometric measurement section, it will be discussed now.

The presentation of Mr. Frechen addressed the concept of Odour Emission Capacity (OEC) of liquids which the speaker has been working on for various years, and presented for the first time to the international communityin 2004 in Cologne, Germany. OEC is defined as the total quantity of odorous substances that can be extracted from a liquid through stripping under predetermined conditions and is expressed in the liquid ou_E/m³. On this occasion Mr. Frechen spoke about the elaboration of a new German guideline VDI 3885/1 that will detail the measurement of OEC in liquids.

Specifically, the following advantages in the application of guideline VDI 3884/1 were delineated:

1. Description of the liquids with respect to the strength of their odour.
2. Description of the different industrial effluents that have been studied very little to date (with the new VDI 3885/1 it will even be possible to establish limits and monitor them later).
3. Identification of problems in odour emissions. In this section an example was given about a large auto body paint plant (1800 automobiles/day).
4. Effectiveness of the dosing methods of chemical products in waste water collectors: In this section the collector Colonia/ Mönchengladbach was discussed.
5. Verification of the impact of odours on changes in industrial processes: On this point the switch from open channeling of waste waters to non-atmospheric sewer pipes and their influence on odour emission was discussed.

Estimate of the release of odour in drops in waste water levels in wastewater pipelines.

The OEC will be a very useful tool when designing odour treatment systems in liquid transfer systems (pipes, pipelines, deposits, decanters, etc.) that will require one more turn of the screw in the broadening of knowledge on urban and industrial waste water odour emissions.

ACCREDITATION OF ODOUR CONSULTANCY COMPANIES

 

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After the coffee break the conference moved on to the next section dedicated to the accreditation of odour consultancy companies. This section was moderated by Mrs. Franzen-Reuter.

The first presentation in this section was given by Mr. Wagner, Chief of Department in the German city of Essen of the Ministry of Climate Protection, Environment, Agriculture, Nature and Consumer Protection in North Rhine-Westphalia. His presentation was titled quality assurance in the identification of odours as the basis for securing accreditation.

The presentation of Mr. Wagner shed light on notifications (Notifizierung o Bekanntgabe) and accreditations (Akkreditierung) in Germany.

In Germany big changes have been made after having various accreditation entities at a state level in the past ⁽³⁾.

Determining the emissions and immisions in Germany is carried out by independent private companies that are qualified to perform these measurement tasks at the request of operators or regulatory agencies. The technical competence of these companies is confirmed through accreditation⁽⁴⁾  for an individual determination.

Competence includes, in addition to the technical outfitting of the testing laboratories corresponding to the foreseen activities, the operation of a quality management system and an aptitude test for the staff in charge at the accredited company, measured through high quality and expert reports.

The competence test for the testing laboratories accredited and “notified” regarding the adequate implementation of the measurement methods is guided by the results of their participation in laboratory proficiency testing. The evaluation criteria are the precision of the measurement results during these proficiency tests, along with the estimate of uncertainty associated with the measurements. Likewise, the experience in the employment of measurement methods, planning and the evaluation of results must be demonstrated.

For certain research in the legal and regulatory field, in addition to accreditation, it is necessary to obtain recognition from the proper authorities. To do this, some additional requirements are essential beyond some professional competency tests. These requirements are submitted to continuous state monitoring, which verifies the quality of the measurement method as well as its application and the documentation of the results.

The next presentation was given by Mr. Krieger, a specialist and analyst from the LGA Landesgewerbeanstalt, a certification company headquartered in Bavaria, Nuremberg. The title of his presentation was “Accreditation of odour consultancy companies according to DIN EN ISO / IEC 17025, the focus of the German Accreditation Service (DAkkS)”.

Mr. Krieger noted that securing a notification based on section 26 of the Germany Law for Federal Immision Control is a prerequisite for carrying out odour determinations and is therefore necessary for the majority of the olfactometric testing laboratories in Germany. Securing a notification implies both compliance with requirements of the ISO 17025 and compliance with the directive on notifications.

In the majority of German states this is a prerequisite for the successful completion of an accreditation process. In the presentation of Mr. Krieger the different causes that can influence the time necessary for securing a notification and/or an accreditation were presented.

Although the procedures have been significantly improved through the participation of mixed cooperation committees between the Dakks and the state authorities, notification and accreditation are formally two independent processes; the time required for these processes should not be underestimated. Mr. Krieger noted in his presentation that adequate planning is always necessary, with sufficient time in advance to ensure beforehand that all of the documents are complete and that they comply with the standards required in each case.

The next, and the last, presentation in this session was dedicated to the accreditation of olfactometric testing laboratories and given by Mr. Van Harreveld, General Director of the Odournet Group and was titled “The practice of accreditation audits for ISO 17025 in olfactometry laboratories in the European Union.”

Mr. Van Harreveld discussed the special characteristics of German notification, pointing out that this type of precept does not exist in any other European country. In theory, a testing laboratory needs to have an accreditation to be able to have a notification, however in practice, of the 28 olfactometry laboratories in Germany that operate according to the guideline EN 13725, only 15 are currently both accredited and notified ⁽⁵⁾.

The current situation in Germany, where both the accreditation and the notification coexist in similar terms without a clear definition of how the two mechanisms interact, seems contrary to the European Guideline 765/2008 that requires a clear choice if an alternative system of notification is to be maintained.

Of the 28 olfactometric laboratories in Germany, only 13 participated in a laboratory proficiency test 2011, which, according to Mr. van Harreveld, is the cause of deep concern as it seems that the requirements for accreditation in Germany are less demanding than in other European countries.

In this sense the speaker recommended that the methods and processes of accreditation in Europe be harmonised to the extent possible to reduce the apparent differences in the levels of rigour in the auditing of olfactometric laboratories.  

After a brief pause in which the above issues were debated, work was concluded for the day.
 

PROGNOSIS OF ODOURS.

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This part of the conference was moderated by Mr. Both.

In the first conference, Mr. Hartung, from the Department of Technology of Agricultural Processes at the University of Christian-Albrechts discussed the state of development of part 2 of the VDI 3894 “Emissions and immisions on Farms. Types of stabling and emissions. Pigs, cattle, poultry and horse raising.”, Method for Determining Distance (distance control). Odours.

The completed draft of part II of the VDI 3894 has still not been approved ⁽⁶⁾, at least as of this conference in Baden-Baden. The German guideline VDI 3894 describes a simplified method for the evaluation of odour immision in farms through the calculation of setback distances. This guideline will substitute guidelines VDI 3471, VDI 3472 and the drafts of VDI 3473 part I and VDI 3474. Part II of the VDI 3894 develops what was described in part I on the state of the art and measurements necessary to lower the emission of odours on pig, beef, horse and poultry farms. In part I the limit values are also described (as well as ammonia and suspended particles) based on which the use of a dispersion model is necessary.

The minimum setback distances of farms with respect to populated areas described in the German guideline VDI 3894 part 2 have been established according to the current state of scientific knowledge and have been based on the data of numerous odour measurements carried out on a large number of farms with pigs, cows, horses and birds. Likewise, the results of an enormous number of calculations carried out with the dispersion model AUSTAL2000 have been taken into consideration. For the estimate of setback distances of farms with respect to human populations, various test emission sources have been taken and different conditions of propagation have been studied, based on empirical experience with the assistance of regression analysis.

The distances determined in this way correspond with certain odour frequencies in the proximity of farms that can be evaluated depending on the imission situation. Through the procedure described in guideline VDI 3894 part II the different odour frequencies are established in a simplified way based on setback distances which are based on calculations performed with a dispersion model. In addition, methods are established to determine the total contribution of odour in case various farms are located in the area.

The equation used for the calculation of the setback distance is the following:  
R = a•Q^b + d_r
where,

R: Setback distance
a: Coefficient dependent on wind direction and the frequency of odour-hour
Q: Odour emission from the source (in ou_E/s)
d_r: Additional separation dependent on the geometry of the source

For a more detailed analysis of the equation used to determine the setback distance and of the methods used to determine the odour emissions of multiple farms, a review of VDI 3894 part II ⁽⁶⁾ is recommended.

The next presentation in this session was given by Mr. Puhlman, Chief of the prognosis Area of the Immision, odour research, asset analysis at TÜV NORD Umweltschutz GmbH & Co. KG in Hamburg. This presentation was titled Dispersion Models. Limits in the application of Model AUSTAL2000G.

The restrictions in the use of the odour dispersion model AUSTAL2000G and the field wind diagnostic model (TALdia) are normally due more to the low availability of sufficient representative meteorological data than to the actual Langrangian model itself.

Most of the time, experts have to confront situations that are not within the normal range of the AUSTAL2000G model, so alternative methods must be selected. For example, one constraint of this model is that the height of the source (commonly chimneys) must be at least 1.2 times greater than the height of the building where they are located. When the chimney is close to the roof of the building, pragmatic solutions can be found through different approaches, which can in some cases result in unwanted overestimates.  

The combination of different prognosis field models for meso-scale winds can be helpful in cases where the slope of the land in the study areas is too steep. In the case of nearby buildings located downwind from the source predictive models at a microscale can be combined with AUSTAL2000G.

In general, it is not always easy to find the most adequate solution. Many experts do not consider these drawbacks, such that the results of the modelling are questionable at the very least. In this presentation, Mr. Puhlmann discussed two types of common problems: 1) the large number of emission sources close to the ground; and 2) emission sources close to the ground on land with steep slopes.

Both cases dealt with the diverse approaches carried out to determine the total odour emission in these types of situations.

The next presentation was given by Mr. Hartmann, who discussed the needs and opportunities in the evaluation of odour immision in the context of a substantial modification of an Environmental Authorization. Mr. Hartmann works in the Institute for Environmental Protection ANECO GMBH in the city of Mönchengladbach.

With the introduction of the procedure for the Authorization of a substantial modification of a plant considering section 6 ⁽³⁾ of the German regulation BImSchG (Germany Law for Federal Immision Control) it is possible to grant an authorization, even when the exposure values are exceeded. Nevertheless, this regulation is the best alternative possible for odour evaluation, due to the previous introduction of the Directive for Odour Immisions.

In the presentation given by Mr. Hartmann, two case studies were described focusing on two plants subject to a substantial modification procedure in which the applicants had to identify and repair odour emissions. In both cases the estimates in VDI 3940 were used with respect to the values established in the GIRL guide in addition to measures through dynamic olfactometry.

This work presented the opportunities and difficulties of both the applicants as well as the regulatory authorities. Likewise there was discussion on the use of frequencies of odour-hours as a tool for assessing the odour impact of a plant and there was a comparison with the use of odour intensities to verify the effectiveness of the corrective measures applied.

After a coffee break the group continued to the following section of presentations titled “Interpretation of Odours”.

INTERPRETATION OF ODOURS.

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The moderation of this session of presentations was performed by the previous speaker, Mr. Hartmann.

In the first presentation of this section Mrs. Gallman presented the different criteria for evaluating the presence of odour surrounding the farms. Mrs. Gallman is an Academic Advisor in Process Engineering of Livestock Systems, from the Institute of Agricultural Engineering at the University of Hohenheim.

Source VDI 3474-“ (2001)

The focuses for the evaluation of odour emissions from cattle can be divided into 1) regulations oriented towards the sources that regulate the setback distance; and 2) regulations that limit the frequency of odour-hours or the odour concentration. Both focuses offer ways to ascertain the differences between species in the weighting factor of animal mass, the number of animals or the characteristics of the environmental air.

This work described the principle of evaluation for the setback distances for different species of livestock through a weighting of the sources, their transmission to the air and the immision parameters. Below, these calculations are contrasted with the agreements made in the Directive for odour Control in Germany and with legislation based on limit values of exposure to odours in Holland and other countries.

For example, for a farm with 120 dairy cows stabled in cubicles, the setback distance with respect to a populated area can vary depending on whether the climate conditions are unfavourable or favourable between 59-98m in Austria, 67-101 m in Switzerland and between 73 and 145 m in Germany ⁽⁷⁾.

The following presentation was put together by Mr. Both that discussed some issues of interpretation of the German Directive GIRL ⁽⁸⁾.

The GIRL Directive includes a procedure for the detection and evaluation of odour emissions and is linked to the German Law for Federal Immision Control (BlmSchG) and with the Technical Instructions for Air Quality Control (TA Luft). The GIRL Directive is used in all of the German states to evaluate odour emissions and establish a framework so that experts as well as officials of regional environmental ministries can arrive at an adequate evaluation of the situation in case they forsee, or if in fact there are, odour emissions. However, due to the large number of possible scenarios, questions always arise when the test is designed and the sample collected.

In the presentation given by Mr. Both, different and interesting aspects related to the GIRL Guideline were discussed; these aspects are subject to different interpretations. The cases presented were the following: 1) determining the evaluation area; 2) the inclusion of farm odour control equipment; 3) the consideration of the real or authorised yield for a plant; 4) the typical scenarios in case the value of inmission is exceeded; and 5) consideration of the odour emissions of dairy cows not kept in stables.

Each one of these cases was dealt with in detail, highlighting possible questions and interpretations of the German GIRL Directive.

Lawyer C. Mohr was in charge of the next presentation, she presented her perspective on the management of odour emissions in urban planning: the designation of construction areas close to industrial areas and the distribution of the odour emission components in plans for urban zoning.

Odour emissions can represent an important problem, if those responsible for the development of an urban centre plan to design new residential areas close to activities that could potentially emit odours. During the process of urban planning, the interests of odour emitting industries should be taken into consideration in the most reasonable way possible. Prior to the environmental evaluation of this development, all public and private interests should be considered very carefully. This includes considering not only the interests of the companies in maintaining production but also the potential expansion of local industries. If conflicts due to odour emissions are probable, a detailed review and possible modification of the urban development plan is inevitable.

The same principle is applicable in the development of new expansions for industries that could potentially be emitters of odours in the surroundings of residential areas. According to the Federal Ordinance of Urban Use, corrective measures must be established in the urban development plan to prevent conflicts with the inhabitants of residential areas due to odour emissions.

After a brief break, the conference continued with the the last section of presentations in which various case studies were discussed.

CASE STUDIES AND PROJECTS

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This last section of presentations was moderated by Mr. Koch.

Mrs. Hammerbacher was in charge of the first presentation in this section. She is Executive Director of Hammerbacher GMBH consulting & projects in the German city of Osnabrück, and addressed the issue of the potential for resolving conflicts through dialogue with neighbours in conflicts over odour – a case study of an industrial area with a large number of odour sources.

In this very interesting presentation, Mrs. Hammerbacher mentioned that the potential of annoyance from odours is subjectively influenced, even when the incidence and the characteristics of the odours can be controlled with recognised methods. Therefore, the potential for conflict or the resolution of conflicts over odour emissions depend on such factors that can only be dealt with through communication.

For this reason, there should be a coexistence of new reasons for reaching an open space for all interests, build mutual understanding, recognise areas of work and find concrete and flexible solutions to conflicts over odour. To do this, the author delineates a series of requirements for accepting the emission of odours, which can be divided into various categories.

1)    Passive acceptance through ignorance, which implies silence as consent and the feeling of a lack of importance
2)   Passive acceptance through resignation, in which the neighbours think that nothing can be done, which is accompanied by latent emotions and possible conflicts.
3)   Active acceptance through understanding, which implies that the neighboring population assumes that the odour is acceptable and could occur occasionally.

In this sense Mrs. Hammerbacher defines acceptability as a term constructed by interests, perceptions and expectations of a group of people.

The author proposes an in-depth study of the situation asking the following questions: Who is “affected”? In what way are they affected? What is expected from dialogue? In what groups will the opinion modelling be performed? Who is interested in dialogue?

The author proposes a dynamic conflict space as reflected in the following figure.

Chart 3. Dynamic conflict space. Reproduced with permission from the author. Source: Hammerbacher

For this researcher, precision is very important in conflict resolution.

The following table delineates a series of misunderstandings that can lead to potential conflicts and a clear area where work is needed to resolve them.

Type Cause  Treatment Conflict of interests The conflict is correctly perceived. Example: bad odours. Solution or compromise Latent conflict A pre-existing conflict, that continues to move. Ex: historical events Transparency Conflict assigned incorrectly There is a conflict between the wrong parties. Ex: Residents and company A  instead of company B Transparency Conflict delimited incorrectly The parties discuss different things. Ex: health risks instead of odour emissions. Transparency Conflict of perceptions  The conflict depends on circumstances that are not perceived: Ex. Other odour emissions. Transparency Apparent conflict The conflict stems from misunderstandings or erroneous perceptions. Ex: Preferring odours on the weekends. Transparency

Table 4: Precision in conflict resolution. Reproduced with permission from the author, VDI Gerüche in der Umwelt. Source: Hammerbacher, citing Fietkau, WZB, 2000.

Communication and dialogue structured between those that are affected by the odours and those that emit them, opens the possibility that the emitter and the affected party will get to know each other better. It allows for direct communication and personal contact between those in charge of the plant and the representatives of the affected population. This changes the interpretation and subjective evaluation of the emitter of the emissions from the perspective of the local residents and social groups. Along these lines, there was a presentation of a specific case study on conflict management that was performed in an industrial area, where 4 companies were located and were potentially odour emitters, close to a population where numerous complaints about odours had been lodged.

In this interesting test case the preparations for the dialogue with affected neighbours is described in detail, including the construction of a direct line of communication, dialogue between the accused companies, the balance struck after the initial contact and the description of the relationship between the objective measurement of an odour and the subjective perception of them.

The next presentation given by Mr. Geburek addressed the representation of temporal series to describe the odour emissions from chicken farms and their impact on the result of an immisions prediction.

Odour emissions from cattle depend on the number of animals stabled. On poultry farms and in particular on chicken fattening farms, this odour emission increases by 60 times during the short breeding cycle of 40 days. This influences the behaviour of the dispersion and the resulting immisions. In his presentation Mr. Geburek gave examples of different scenarios depending on the emissions being considered.

To do this the case began with a chicken farm of 39,000 animals with a surface of 1788 m² and with 16 emitting sources with an average flow of 21,000 m³/h. The height of the sources was set at 10 m with an average windspeed of 7 m/s.

With this data three types of emissions were considered:

1)    Constant emissions of 60 ou_E/s per animal unit
2)    Time-dependent emissions of 180 ou_E/s per animal unit
3)    Emissions dependent on the surface of the the farm and the temperature

For each one of these scenarios a dispersion model of the odours was carried out and their results compared, demonstrating the path towards a more adequate calculation of these emissions and guiding the process of environmental authorization of cattle facilities.

The next presentation was given by Mr. Broer, Director of the Department of emissions and immisions from the Institute of Soil and Environment, LUFA Nord-West, en Oldenburg. On this occasion the speaker discussed the reduction of odour emissions on farms through the treatment of exhaust air. How reliable is the certified treatment equipment in practice?

The LUFA institute, with over 150 years in existence, has proven competence in various fields, one of which is cattle.

It is possible to evaluate the capacity of gas treatment equipment by using various approaches. For example, the Testing Centre of the Germany Association of Agriculture (DLG) has a testing protocol for “treatment equipment for odours on farms” through a Signum test. Since 2005 the capacity of several odour treatment equipment have have been measured, especially bio-filters and bio-trickling.

In addition to the yield in odour treatment, ammonia and particles, there has been a determination of the dimensions of the equipment, the use of electricity, water and chemical products; there has been a review in the management plans, maintenance costs as well as personal and team security.

During 2010 and 2011, the LUFA Nord-West Institute has carried out the evaluation of the official measurements of 96 units of treatment equipment. Of these 96 measurements, 56 corresponded to initial audits and 40 were verifications following a period of time in operation.

During the evaluations it was observed that 17 of these 96 sets of treatment equipment went above the criteria established as a limit. In some cases the odour of the gas at the entrance was detectable in the clean air at the exit and in other cases exceeded the limit value of 300 ou_E/m³.

In other words, some 18% of the odour treatment equipment did not comply with the established criteria for treatment. In reality all of the instances where the limit value of 300 ou_E/m³ was exceeded, malfunctions were reported in the treatment systems due almost exclusively to a lack of equipment maintenance.

In conclusion, Mr. Broer called attention to the fact that the research showed that regular monitoring is essential for the proper functioning of equipment.

The last presentation of these conferences and therefore the last of this section was to be given by Mrs. Schwarzböck, but in her place Mr. Frechen closed the conference. However, this article follows the order established in the initial programme, given that the presentation of Mr. Frechen was mentioned previously.

Mrs. Schwarzböck, manager of the Centre of Competence for Water spoke about the use of electronic noses as a tool for odour management in Waste Water Treatment Plants (WWTPs).

In the impressive facilities of the Berlin Centre of Competence for Water a series of experiments are being carried out in a large scale channelled water circuit. In this circuit that carries waste water from Berlin, the abilities of four multigas sensory systems currently available on the market are going to be tested (sometimes called Electronic Noses). The first results are expected to be available in 6 months, in which the real process conditions will be simulated with the aim of demonstrating the applicability of these systems for the management of odours in pipelines with urban waste water.

Currently there is no guideline or guide to carry out a test with these characteristics, therefore a method has been developed that will allow an assessment oriented to the applicability and the innovation of each system following – to a certain extent – the methodology in EN ISO 9169. The criteria established will be adapted and broadened to the measurement concepts of the Electronic Noses and the experimental conditions. The research programme is designed in such a way that different cases of application will be covered (for example, the planning of an additive dosing strategy for the control of odour emissions in sewers).

This is the first experiment of this type that has been done with Multigas Multisensor Systems from different manufacturers at such a large scale and will be useful for learning about the advantages and drawbacks of this type of equipment.

With this presentation, the conference on odours in the environment was concluded with a positive reception from attendees. There have been conferences for several years now from the Association of German Engineers VDI and I must say that the content as well as the organization of these conferences is always inspiring and interesting.

This year there was no simultaneous translation like the previous year, so the attendance fell considerably compared with the conference held in 2009 in the same place; this was perhaps also due to the current economic climate. Of course, the attendance records from the conference organised in 2007 in Bad Kissingen or Cologne in 2004 have not been broken yet.

This article has been financed in part by the company LABAQUA.

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NOTES:

(1)    Denomination proposed by the odour pollution group from CONAMA.

(2)    Analagous with the unit commonly utilised for noises (dB), the level of odour can be expressed in decibels (dBo), as long as they refer to a reference concentration threshold of 1 ou_E/m³. The odour decibel dBod is the decimal logarithm (log10) of the odour concentration, multiplied by 10.

(3)    State legislation in Germany refers to the different legislation in each one of the 16 German states, so when it is mentioned “state” legislation this refers to 16 different regulations. To speak about national legislation it is better to use “federal” legislation.

(4)    Unlike the rest of European countries, in the past Germany didn’t have a single entity of accreditation, but rather had a fragmented system of some 20 private and public entities of accreditation. However, because of European Regulation (CE) Nº 765/2008, the creation of a single accreditation entity became necessary. The Dakks began operating on the 1^st of January 2010. This German accreditation entity has the difficult task of bringing together the different existing criteria, among them those relating to the concession of “accreditations” and “notifications”.

(5)    Four German laboratories have notification but they are not accredited and 9 laboratories have accreditation from Dakks but nevertheless do not have notification.

(6)    The documents and VDI guidelines are found in German during the draft and elaboration phases, being translated into English once they are published as approved.

(7)    89-145 m if the VDI 3474-E and 73-125 m are followed according to the guideline VDI 3894-2VE.

(8)    GIRL is the denomination in German of the Geruchsimmissions-Richtlinie, in other words the Directive on odours in the environment.

TABLE:

Table 1: Precision (r) and accuracy (A) for 19 laboratories. Reproduced with permission of the author. Both, R.; Müller, F. (2011): Überlegungen zur Messunsicherheit bei olfaktometrischen Messungen – Eine Auswertung der n-Butanol-Daten von 19 Laboratorien. In: VDI Wissensforum GmbH (Hrsg.): Gerüche in der Umwelt. VDI-Berichte 2141, S. 43–54

Table 2: Measurement results of the repeated measurements (odor level). Reproduced with permission of the author. Both, R.; Müller, F. (2011): Überlegungen zur Messunsicherheit bei olfaktometrischen Messungen – Eine Auswertung der n-Butanol-Daten von 19 Laboratorien. In: VDI Wissensforum GmbH (Hrsg.): Gerüche in der Umwelt. VDI-Berichte 2141, S. 43–54

Table 3: 95% confidence interval, depending on the level of uncertainty. Reproduced with permission of the author. Both, R.; Müller, F. (2011): Überlegungen zur Messunsicherheit bei olfaktometrischen Messungen – Eine Auswertung der n-Butanol-Daten von 19 Laboratorien. In: VDI Wissensforum GmbH (Hrsg.): Gerüche in der Umwelt. VDI-Berichte 2141, S. 43–54

Table 4: Precision in conflict resolution. Reproduced with permission from the author, VDI Gerüche in der Umwelt. Source: Hammerbacher, citing Fietkau, WZB, 2000. Hammerbacher, R.; Hartmann, U. (2011): Das Lösungspotenzial von Nachbarschaftsdialogen bei Geruchskonflikten Am Fallbeispiel eines Industriegebiets mit einer hohen Anzahl von Geruchsquellen. In: VDI Wissensforum GmbH (Hrsg.): Gerüche in der Umwelt. VDI-Berichte 2141, S. 189–196

CHARTS:

Chart 1: Precision r and accuracy A for n-butanol according to EN 13725.

Chart 2: Precision (r) on a supposed measurement of 532 ouE/m3 from each testing laboratory for a confidence interval of 95%.

Chart 3. Dynamic conflict space. Reproduced with permission from the author. Hammerbacher, R.; Hartmann, U. (2011): Das Lösungspotenzial von Nachbarschaftsdialogen bei Geruchskonflikten Am Fallbeispiel eines Industriegebiets mit einer hohen Anzahl von Geruchsquellen. In: VDI Wissensforum GmbH (Hrsg.): Gerüche in der Umwelt. VDI-Berichte 2141, S. 189–196

 

 

If you find this article interesting, you might be also interested in these articles.

• VDI Conference. Odours in the environment 29-30 Nov 2011. We see each other again in Baden-Baden, Germany
• VDI Congress Programm Odours in the Environment 2011
• Odours in the environment 25-26 Nov. 2009 in Germany
• Seminar About Odours In The Indoor And Outdoor Environment
• Odours in the Environment (update)

Content

Odours

What are Odours?

Odours are defined (1) as the resulting sensation of the reception on a stimulus by the olfactory sensory system. The way the human respond to an odour stimulus depends on its sensory properties, in particular, Odour Concentration, Intensity, Quality and Hedonic Tone. The combined effect of these properties is related to the degree of annoyance that an odour can cause.

Odour Concentration

The odour concentration is defined within the European Standard EN 13725 as the number of European odour units in a cubic metre of gas at standard conditions. Therefore, the odour concentration is measured in "European Odour Units" and its symbol is "uo_E".

In short, the odour concentration has similar characteristics than decibels in the sense that they are both properties linked to the human senses. The odour concentration is calculated from the number of times that an odorous gas has to be diluted in order to reach the odour threshold of a group of people or panel specially trained and selected, but with a normal sense of smell. In fact, the geometric mean of the individual odour threshold of each person is calculated.

Wait a minute ¿what is the odour threshold?

The odour threshold of any odorant is the minimum concentration at which anybody with a normal sense of smell is able to detect it. It is also called the detection threshold and it has a couple of more technical definitions in the EN 13725, but we will not go there.

The process can be better explained with a simple example. Let's suppose that we have an odorous gas (that is, an odorant) and we dilute it with odourless air 10 million times. Probably, when we present this gas to be smelled by a member of a panel, she (or he) will not detect anything. If we dilute the odorant less and less, there will be a moment in which this person will be able to detect the diluted mix. This way, if the gas has been diluted 30 times with odourless gas in order to reach the detection threshold, it is estimated that the initial odour concentration of the gas was 30 uo_E... for this person, of course.

Statistically that is a bit weak, so the same procedure is made for a group of minimum 4 people. In this case, the geometric mean of the individual odour thresholds is calculated and this way we get the odour concentration of an odorant. The important fact to take into account here is that it does not matter the people that participates in the measurement, it does not matter if they are male or female, young or not so young, if they are from China or from Belgium, the result will be repeatable and reproducible within an uncertainty range.

The measured values depend, of course, on the kind of sensory test, the selection of the panel, the criteria of detectability and other factors.

Odour Intensity

In fact, Odour concentration does not inform about how strong is an odour perceived. In contrast, odour intensity does bring information about the degree of annoyance of an odour, that is, odour intensity express the strength of the odour sensation.

Let us suppose using another example that we could measure a sample of odour collected from the vicinity of a restaurant. If we got a concentration of, let's say 10 uo_E. ¿Does this mean that the annoyance perceived by the neighbours is 10 times higher than when there was no restaurant?

The answer is NO.

Unfortunately, the "Concentration" magnitude is not lineal and depends on many factors. An odour can remain undetected above a certain concentration, its composition may have alterations, its hedonic tone could change from an "annoying odour" at low concentration, to a "pleasant odour" at higher concentration (or the opposite), or it could be perceived with the same degree of annoyance with 2 uo_E or with 15 uo_E.

Odour intensity is the strength of the perceived odour sensation and in many cases It is related with the concentration of an odorous substance. The following equation could define the relation between Odour intensity (I) and concentration (C). “K” is a constant and “n” is the exponent.

Also

This is known as Stevens' law or the power law. For odours, n ranges from about 0.2 to 0.8, depending on the odorant.

For an odorant with n equal to 0.2, a 10-fold reduction in concentration decreases the perceived intensity by a factor of only 1.6; whereas for an odorant with n equal to 0.8, a 10-fold reduction in concentration lowers the perceived intensity by a factor of 6.3.

The dependence can also be described as a theoretically derived logarithmic function according to Weber and Fechner (2):

where C0 is the threshold concentration; and kw is the Weber-Fechner coefficient or Weber ratio.

Which one of these 3 equations applies depends on the method used. To this date, no theory has been able to derive the psychophysical relationship from knowledge about the absolute odour threshold of various substances.

Odour intensity is determined in ambient air by means of odour inspections. There are a few standards on the calculation of odour intensity in ambient air such as the ASTM E544-18 or the much used VDI Guideline 3882 sheet 1.

The following table illustrates the different levels of intensity that can be registered in a field inspection according to the VDI 3882.1.

Odour	Intensity stage
not perceptible	0
very faintly	1
faint	2
distinct	3
strong	4
very strong	5
extremely strong	6

Odour Quality

Odour quality or character is that property that identifies an odour and differentiates it from another odour of equal intensity. Basically this parameter provides information about what the substance smells like.

The odour character is described by a method known as multidimensional scaling or profiling. In this method, the odour is characterized by either the degree of its similarity to a set of reference odours or the degree to which it matches a scale of various descriptor terms. The result is an odour profile.

Odour Hedonic Tone

Hedonic tone is a property of an odour related to its pleasantness.

When the hedonic tone of an odour is evaluated in the neutral context of an olfactometric presentation, the panellist is exposed to a controlled stimulus in terms of intensity and duration. The degree of pleasantness or unpleasantness is determined by each panellist experience and emotional associations (3).

A distinction has to be made between the acceptability and the hedonic tone of an odour. When an odour is evaluated in the laboratory for its hedonic tone in the neutral context of an olfactometric presentation, the panellist is exposed to a controlled stimulus in terms of intensity and duration. The degree of pleasantness or unpleasantness is determined by each panellist's experience and emotional associations.

Other Properties

  Although Intensity, Concentration, Character and Hedonic tone are intrinsic properties of the odours, there are other important parameters related with this sensation that have a certain importance, sometimes a neat one. For example the persistence of an odour is related to the change in the odour intensity when diluting an odour. The frequency of an odour is the percentage in time that is possible to detect this odour in the atmosphere. For example the German norm VDI 3940 defines the odour frequency as the percentage of odour hours in a year, defining the percentage odour time as the ratio between the time fractions that an assessor is able to recognize an odour and the total measurement duration.