The Odor Management Blog

Are Factories Solely Responsible for Odor Problems?

Where their is odor, there is blame. And its usually municipal and industrial sites that get the blame. Most people never consider that naturally occurring odors could be the real source.

In fact, at Odotech, we used our odor measurement methods in private studies to show that the odor generated by some swamps was very easily confused with the odor from a nearby landfill site.

Swamp gas is produced by the fermentation of organic matter. The spontaneous ignition of this gas causes will-'o-the-wisp, which has given rise to many medieval legends. This swamp gas is a natural biogas consisting of methane and VOC, H2S, and various strong-smelling organic compounds, just like the biogas produced in landfill sites and methanization units. The tests showed that from a typical dilution level representative of the odor exposure to local residents, most people found it impossible to tell the difference between the swamp odor and the landfill odor.

Another example comes from urban areas where the residents are bothered by unpleasant odors like rancid butter or vomit. This odor comes from a beautiful tree: the Maidenhair tree, or ginkgo biloba. These trees have no seeds, but the male specimens have cylindrical catkins, and the female trees have ovules, containing butanoic acid. This chemical substance is the source of the nasty odor.

Another source of odor are the edges of bodies of water, that given the right conditions, are sometimes a source of hydrogen sulfide (H2S) odors. The proliferation of algae that can accumulate in stagnant water and then decompose anaerobically generates H2S emissions smelling like a sewer. In larger bodies of water, the tide can bring in organic materials and algae, which build up on the shore, causing major odors when they decompose.

As a factory or plant manager, you are no doubt conscientious about limiting the release of odors into your local environment. But it can be hard to tell how much of the problem is due to industrial or municipal odors, and how much comes from natural odors that are beyond your control.

The OdoWatch odor monitoring and tracking solution will let you determine the incremental impact of the odors caused by specific activities. With Electronic Noses (e-noses) positioned near the odor sources, combined with real-time 3D odor monitoring, you can tell your odor contribution apart from the general background smells.

This can bring significant savings in operating costs as well as reducing complaints and fines. Using OdoWatch's objective data to show the community, the authorities, and your neighbors the limited extent of your contribution to the odor environment, will be a benefit to your plan and put everyone under less pressure.

How to save on your landfill odor emission assessment

 

Methane in municipal solid waste landfills (MSWL) is produced through anaerobic microbial degradation of organic matter. When the conditions of methanisation are stable in wastes, landfill gas is mainly made up of methane (CH₄) and carbon dioxide (CO₂) in about equal proportions. The stable production of methane, a source of usable energy, can last several years. However, biogas contains others gases in trace amounts, primarily sulfur compounds and volatile organic compounds (VOCs).

The methane and carbon dioxide are greenhouse gases like some of the trace gases (for example, chlorinated and fluorinated organic compounds). Landfill gas has other environmental and health risks: in addition to the potential of explosion, harmful effects exist because of the presence of hydrogen sulfide (H₂S) and of potentially toxic VOCs (benzene, vinyl chloride, dichloromethane, chloroform, toluene, dichlorobenzene, etc) as well as compounds responsible for odors (VOCs, sulfur compounds, etc).

Quantification of landfill gas emission is thus most important but could be time and money intensive considering the extent of surfaces to repeatedly cover. Since heterogeneity must be expected over these large scale areas, a single sampling point method can not be used.

The Instantaneous Surface Monitoring (ISM) (Rule 1150.1, South Coast Air Quality Management District, California) is an interesting method to locate hot spots of landfill gas emissions and determine a cell emission heterogeneity over the full surface. However, this method will not provide the CH4, odorants, odors, toxics and VOC emissions as a quantitative value in emission per unit of surface over time.

We would like to introduce here a method that we have developed with extensive R&D efforts and have been using over a decade on numerous landfills in North America and Europe.

The basis is to perform a overall profile of the methane surface concentrations and to establish the correlation between methane surface concentration and the methane surface flux. The Total Volatile Organic Compound Methane Equivalent (TVOCME) ground concentration cartography is performed according to the recommendations of the instantaneous surface monitoring (ISM) method described in the Californian rule 1150.1. The methane surface flux is measured with a dynamic flux chamber operated according to the recommendations of the US EPA (Klenbusch, 1986).

The analysis of the flux chamber gas can cover several parameters depending on the purpose of the emission assessment : potential toxicity, respect of the standards, potential olfactive nuisance, limonene, careens, camphene, pinene, phellandrene, sulfur compounds, mercaptans, sulfides and VOCs (ethylbenzene, styrene, toluene, benzene, etc).

Several analytical methods are adapted to MSWL emissions characterisation and they are powerful and recognized techniques:

• Portable FID, GC-FID or GC-TCD for the methane and the carbon dioxide,
• GC-MS with cryogenic trap for the VOCs and the other organics like terpenes (method TO-14A of the US EPA),
• GC-PFPD for the sulfur compounds
• Olfactometry with dynamic dilution (methods ASTM E679, EN 13725, probit) for the odours.

 

 

 

 

 

 

The following graph presents an example of Total Volatile Organic Compound Methane Equivalent (TVOCME) ground concentration distribution. The red dots are locations selected for "high quality analysis" with flux chamber sampling.

Based on a limited number of flux chamber samplings and measurements (chemical analysis or dynamic dilution olfactometry), the mass flow rate or odor flow-rate of each cell is estimated using a co-krigging method.

The Y axis is surface flux rate (g/m²/s, ou/m²/s)

This method:

1. Reduces the number of sampling points
2. Provides the distribution of surface emissions for optimization of gas collection system
3. Evaluates the chemicals or odor flow rates of a complete cell for air quality assessments, odor studies or green house gas emission balance.

REFERENCES

ASTM (1997). E679-04- Standard Practice for Determination of Odor and Taste Thresholds By a Forced-Choice Ascending Concentration Series Method of Limits. American Society for Testing and Materials.

CEN European Standard EN 13725 (2003). Air quality - Determination of odour concentration by dynamic olfactometry. Brusssels, CEN.

Klenblusch, M. R. (1986). Measurement of Gaseous Emission Rates from Land Surfaces Using an Emission Isolation Flux Chamber. Las Vegas, NV, U.S. Environmental Protection Agency.

Landfill Odor Monitoring: Optimizing every $ invested

You are a landfill operator and your intention is to do your very best to be a good neighbor. However, from time to time odors originating from your activities are perceived beyond your fenceline. This situation appears unavoidable, however it can be minimized through the application of a systematic odor management approach. Odor monitoring and odor assessment will provide you with better understanding of the problems, provide the data required to optimize your investiment in odor reduction efforts and result in minimized odor episodes.

One of the typical question first faced by an operator is if odors or odorants are to be quantified first to better understand the extent of the odor impact ? Odors in terms of the odor concentration or Odorants in terms of the chemical compounds perceived by the human nose?  Another question is : how can the overall cost of the quantification be reduced while still providing the required information?

Since 2000, we have done numerous emission assessments (odors, odorants, methane and toxics) on municipal solid waste landfills (MSWL). We undertook a large scale study to examine the impacts on the air quality of several MSWL in the province of Quebec in terms of odors and potentially toxics compounds related to biogas emissions.

The project was performed on six MSWL. Assessments of odors and potentially toxic emissions followed by dispersion modeling at each landfill site were performed to estimate the human exposure to potentially toxic compounds and odors. The emissions of selected pollutants, such as volatil organic compounds (VOC), terpenes and sulfur compounds, were estimated by using the landfill gas emission LandGEM 2.01 software and based on field measurements.

The present posting presents some interesting findings specific to odors that we would like to share. But first let’s explain little more about this project:

Experimental procedure overview

In order to evaluate the impacts on air quality of the six landfills, which were selected as representative of the typical landfills in the province of Quebec, 5 stages were proposed:

1. Scientific planning,
2. Experimental measurements,
3. Evaluation of the impacts,
4. Possibility of identifying some(s) tracer(s),
5. Conclusions and recommendations on the methods to monitor and evaluate the impacts on air quality.

The six MSWL represented the three categories defined according to the landfilling capacity.

• A - > 600,000 t/y
• B – 50,000–600,000 t/y
• C - < 50,000 t/y

 

 

Extensive landfill gas characterization and sampling was done at each landfill in the gas collection system and on the surfaces of different working area. The analyzed parameters were selected according to their impact on air quality (potential toxicity, imposed standards, potential olfactive nuisance). The odorous landfill gas compounds are mainly terpenes (limonene, careens, camphene, pinene, phellandrene, etc.), sulfur compounds (mercaptans, sulfides) and some VOCs (ethylbenzene, styrene, toluene, benzene, etc).

In this project, odor measurements were performed by the two usual approaches, sensory analyses and analytical techniques. Sensory odor tests concern the perceived effect of the odorants mixture as detected and interpreted by the human olfactory system (olfactometer). Analytical methods or physicochemical analyses relate to the properties of the odorants (GC-MS, GC-PFPD, etc.).

 

 

 

 

 

 

The odor concentration will take into account the complexity brought by the combination of odourus compounds in a mixture.  The determination of the odor concentration is performed by olfactometric analysis. Olfactometry consists in measuring the odors according to a standardized and recognized procedure.

For the purpose of understanding the contribution of each chemical to the odor concentration, the following ratio was used to define the dilution to threshold (eq odor units) of each odorant.

 

(ODT = Odor Threshold values)

Findings

The following table presents the calculated % for each measured compound, for each compound using the AP-42 factors, the calculated odor concentrations for H₂S and the actual olfactometry results.

1. The dominating odorous compound was H₂S for all sites according to the odor threshold values retained for calculations.  
2. The analytical measurement of odorants consistently underestimated (by two orders of magnitude) the odor concentration compared to olfactometric measurements
3. Poor correlation between odors and odorants concentrations
4. Field values and emission factors of the AP-42 did not identify the same compounds as priority odorants.
5. Priority odorants in LFG:
   • AP-42: 3 sulfur compounds H2S (25%), methylmercaptan (30%), ethylmercaptan (43%)
   • Field measurements: H2S, 55% to 99%
   • The results demonstrate that the odor emissions should be established with the odor concentration determined by dynamic dilution olfactometry and not with the odorous compounds, whether the odorants concentrations are determined by the values of the AP-42 or measured in situ.

Generally, it is difficult to properly characterize odor using standard analytical measurements for atmospheric pollutants. Analytical measurements characterize odors in terms of their chemical composition and the quantification of the odorants by their perception threshold. The number of odorants is very large in landfill gas as in most other environmental odors, and the odorants present were at concentrations lower than or close to the detection limits of the measurement methodologies.
The relationship between the concentration of odorants and the perceived odor is difficult to establish, as synergistic and antagonistic effects are expected between odorants. This is especially true for complex mixtures of odorants. Also, the differences in values of odor thresholds in the literature are very considerable, typically showing a range of several orders of magnitude, relying on these can bring large uncertainties in the calculated concentration.

Recommendations

1. The evaluation of MSWL air quality impact should rely on actual on-site characterization and quantification of the emissions at the source combined with atmospheric dispersion modeling.
2. Since the main impact identified in this research was odor, it is thus recommended to carry out a regular or continuous monitoring of odor emissions in terms of odor concentration.

Odor metrology – Olfactometry vs chemical analysis

 

We have seen the benefits of olfactometry in the blog Measurement of odor emissions – Olfactometry or chemical analysis?

In general, it is difficult to use the chemical analysis method for mixtures of odorous compounds due to the phenomena of synergy, inhibition and masking between different compounds (Gostelow et al., 2003).Complex mixtures, such as environmental air samples, contain many odorous compounds, generally at very low concentrations (Gostelow et al., 2001) (Schiffman et al., 2001) (Parker et al., 2002) (Filipy et al., 2006).  To analyze all the odorous compounds that are present, the composition of the sample must be known in advance, and the detection limits of the chemical analysis devices are often too high to identify and quantify all these odorous compounds (Gostelow et al., 2003).  Finally, the olfactory perception threshold values are not always available in the existing literature, the values reported vary by several orders of magnitude (AIHA, 1989) (US EPA, 1992), and the available references are not recent.

The effects of synergy and masking between different odorous compounds can be observed in samples. For example, in a sample of food odor, the volatile compounds were identified and regrouped in five key odorous families. This was done to study the effect on odor resulting from different combinations of the five groups of compounds (Hallier et al., 2004).  Synergy and masking effects were thus observed.

Numerous researchers have studied odorous mixtures and have created models to predict the effect that the mixtures’ composition has on the perceived odor (composition and concentration) (Gostelow et al., 2003). In general, the use of these models is limited and applies only to the experimental conditions of the study. As well, the mixtures of compounds are mostly studied in the laboratory because of the complexity of mixed odors.

Studies have identified dominant odorous compounds in environmental samples. For example, a positive relation can be established between the odor concentration determined by olfactometry and the odor principle identified in the odor samples of liquid hog manure (Hobbs et al, 2000) and odor samples of composting mushrooms (Noble et al., 2001).  However, these studies also show that a relation between the mixture composition and the odor concentration is still misunderstood and difficult to predict. For wastewater treatment processes, where H2S is the predominant odor, Gostelow and Parsons (2000, from Stuetz and Frechen 2001) show the values of r² between the H2S and the odor concentrations to be as low as 7 to 69%.

Odor Perception Threshold Values

The American Industrial Hygiene Association (AIHA, 1989) compiled numerous studies and established a critical analysis of odor threshold values. The AIHA document is a recognized reference today and is often used as a source for odor threshold values.  The scale of acceptable odor threshold values was established for H2S from 0,001 ppmv to 0,130 ppmv (1 µg/m³ to 181 µg/m³). The recommended value held by the AIHA (1989) is 0,0094 ppmv (13 µg/m³). H2S is a well-studied odorous compound and yet the AIHA proposes a scale of values for the threshold of two orders of magnitude, after their critical review. The example of H2S illustrates why it is often inappropriate to work with odor threshold values because reliable values are not always readily available. New studies with dynamic dilution olfactometers shows 0.0004 pmmv as perception threshold values.

Olfactometry analysis

Olfactometry generates standard sensory analyses, and the principal tool to measure odor characteristics is a trained jury of “noses” or a group of selected experts chosen according to rigorous and precise criteria.  An olfactometer is a device designed to dilute the odorous gas samples and to present these dilutions to the jury. After obtaining the responses of the jury, a statistical treatment of the data permits the olfactometric result to be calculated.

 

Olfactometric analyses are tested in the laboratory (EN 13725 and ASTM E679-04) or in the field during which the odor samples are gathered and then exposed to the target population in the study area. However, olfactometric analyses of ambient air in the field are not recommended because of frequent variations of odor concentrations in ambient air and the low resolution of these methods.

Applications

In England, the Environmental Agency published a guide on the measure of H2S and the reduced sulphur totals at the source of ambient air (Environment Agency, 2001).  This guide recommends that the measuring strategy be directly related to the objective of the measurement study. Thus, if the objective establishes the required abatement to eliminate the nuisance odor, it is specified in the guide that the odor concentration measurements expressed in odor units per cubic meter (o.u./m³) are more appropriate than the kind obtained through chemical measurement. 

Conclusion

The main advantage of olfactometry is the direct correlation between the odor and the sensitivity of the  detector used, i.e. the human nose.  

Despite the advantages of the classic analytical methods (accuracy, reproducibility, etc.), olfactometry remains the best available approach to measure odors directly, in order to objectively quantify the perception of odors.

References

• AIHA (1989). Odor Thresholds for Chemicals with Established Occupational Health Standards. American Industrial Hygiene Association.
• ASTM (1997). E679-91 (reapproved 1997) - Standard Practice for Determination of Odor and Taste Thresholds By a Forced-Choice Ascending Concentration Series Method of Limits. American Society for Testing and Materials: p. 34-38.
• CEN (2003). EN 13725 - Air quality - Determination of odour concentration by dynamic olfactometry. European Committee for Standardization: p. 71.
• Environment Agency (2001). Technical Guidance Note M13: Monitoring hydrogen sulphide and total reduced sulphur in atmospheric releases and ambient air.  ISBN 1 857 05696 5.  Environment Agency’s National
• Compliance Assessment Service, England and Wales.   www.environment-agency.gov.uk/business/techguide/monitoring/m13.html  
• Filipy, J., B. Rumburg, et al. (2006). "Identification and quantification of volatile organic compounds from a dairy." Atmospheric Environment 40: 1480-1494.
• Gostelow, P., SA Parsons (2000). “Sewage treatment works odour measurements.” Wat. Sci.Technol. 41(6), 33-40.
• Gostelow, P., SA Parsons, RM Stuetz (2001). “Odour Measurements for Sewage Treatment Works.” Water Research 35(3): 579-597.
• Stuetz R. and Frechen FB (2001).  “ Odours in Wastewater Treatment. Measurement, Modelling and Control “. Gostelow, P., P.J. Longhurst, SA Parsons, RM Stuetz (2003). Sampling for Measurement of Odours. London
• UK, IWA, 80 pages. Hallier, A., P. Courcoux, et al. (2004). "New gas chromatography–olfactometric investigative method, and its application to cooked Silurus glanis (European catfish) odor characterization." Journal of Chromatography A 1056: 201-208.
• Hobbs, P. J., T. H. Misselbrook, T. Dhanoa and K. Persaud (2000). "Development of a relationship between olfactory response and major odorants from organic wastes." Journal of the science of food and agriculture Vol. 81: pp. 188-193.
• Noble, R., P. J. Hobbs, A. Dobrovin-Pennington, T. H. Misselbrook and A. Mead (2001). "Olfactory Response to Mushroom Composting Emissions as a Function of Chemical Concentration." Journal of environmental quality Vol. 30: pp. 760–767.
• Parker, T., J. Dottridge and S. Kelly (2002). R&D Technical Report P1-438/TR: Investigation of the Composition and Emissions of Trace Components in Landfill Gas, Environment Agency, England and Wales.
• Schiffman, S. S., J. L. Bennett, et al. (2001). "Quantification of odors and odorants from swine operations in North Carolina." Agricultural and Forest Meteorology 108: 213-240.
• US EPA (1992). “Reference Guide to Odor Thresholds for Hazardous Air Pollutants Listed in the Clean Air Act Amendments of 1990” (#EPA600/R-92/047).  TRC Environmental Consultants Inc., S. S. Cha, J. R. Mellberg, G. L. Ginsberg, K. E. Brown, K. Raab and J. C. Coco. US EPA, pp. 93.