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)
- Reduces the number of sampling points
- Provides the distribution of surface emissions for optimization of gas collection system
- Evaluates the chemicals or odor flow rates of a complete cell for air quality assessments, odor studies or green house gas emission balance.
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.
In a previous posting we compared odor impact assessment for a Canadian and a French landfill. Both landfills had been assessed using the same odor protocols and methodologies. Lessons learned from this comparison were that the local wind distribution has a major impact. But just how large is this influence?
In order to understand the influence, we compared the 2 sets of weather data on one of the landfills (the French site for the purpose of this example)
The following figures show the concentration distribution at the 98th and 99.5th percentiles for the French landfill with the alternative meteorological data sets (French and Canadian).
It is interesting to see the significant impact of meteorological data on the concentration distribution. The influence is especially significant further away from the sources (more than 2000 meters), the modeled concentrations can more than doubled.
French landfill: 98th Percentile with French Meteorological Data
French landfill: 98th Percentile with Canadian Meteorological Data
French landfill: 99.5th Percentile with French Meteorological Data
French landfill: 99.5th Percentile with Canadian Meteorological Data
Once again we see that Meteorological data distributions have a major influence on the odor impacts. Based on these real life case studies, we see that the weather data set will have a great influence, up to a factor of 4 for some of the locations in this comparison!
This observation supports the use of local weather conditions to assess the local odor impact. As a matter of fact, a weather station located on site would provide the best data input to the models used for dispersion modeling (provided it is installed and maintained properly).
The client, after reviewing the findings of these odor studies, decided to take a step further into improving the reality of his environmental information relating to odors: He switched over to a real time information system based on electronic noses and an on site weather tower. This allows for real time odor measurements and displays a real time dispersion plume.
During the past few years, there has been increasing public opposition towards waste landfills across North America and Europe. It is believed that this opposition is mainly caused by odor nuisances related to waste disposal and biogas emissions. These nuisances usually bring forward other concerns of the stakeholders, such as the type of wastes being disposed, the management practices and the potential health effects. Odor nuisance is the predominant reason for complaints from existing sites and will trigger objections to new projects. Also, there is minimal data available to benchmark odor assessment results of landfills based on their capacity and biogas collection type.
As seen in the previous blog entitled Odor impact assessment: how and why, odor impact assessments are a very effective and objective method for the quantification of the magnitude and coverage of such nuisances. Odotech has done numerous landfill odor studies, both in Europe and North America. We thought it would be interesting to compare results from a Canadian and a French landfill, both of which where subject of several odor impact assessments over the last decade(using similar methodologies, odor sampling protocols and odor measurement standards).
Methodology used for odor impact assessments
The methodology of an odor-impact study is very similar to that of a health risk analysis or environmental impact analysis. It is based on the characterization of the odorous sources in order to estimate the odor concentration and exposure frequency of the public. First, the main characteristics of the sites were compiled:
- Local data: meteorological data; type of terrain: rural or urban, flat or hilly, etc.; human factors (population density and distribution, occupation, etc.);
- Sources characteristics: emission types (stack, surface source, etc.), source location and dimension, flow-rate and odor concentration.
On landfills two major types of odor emissions sources are typically present and to be quantified : point (flare) and area (closed cells, waste, dumping area). Each requires completely different sampling procedures. Determination of the odor-concentration was performed according to EN13725.
To better estimate the concentration fluctuation, a Gifford-Gaussian model was used. This is especially important since the nose reaches its highest sensitivity for small concentration variations at low odorous gas concentrations and for short exposure times. Because of these two characteristics, the nose is very sensitive to concentration fluctuations of odorous gas in ambient air.
Both landfills are located in flat rural environments and mostly surrounded by farms. For the Canadian landfill, the nearest agglomeration (with a population estimated at 5000) is located at about 3 km from the landfill. For the French landfill, the nearest agglomerations (with populations estimated between 3000 to 5000) are located at about 1 km from the landfill and bigger agglomerations (with populations estimated between 30 000 to 50 000) are located at about 5 km.
Odor flow rates
Both sites have auxiliary activities, for example composting or other type of waste management activities. For comparison purposes, only the domestic waste landfilling related sources are considered here. As shown in the table below, both sites are of comparable sizes (buried waste volume and annual tonnage).
The Canadian landfill has 4 distinct sources while the French site has 9 sources (resulting in a larger overall emitting surface). The following table presents these sources.
Measured odor concentrations or odor flux are presented below. The biogas odor flux was found to be slightly higher in the French landfill. These differences can be caused by many factors: thickness of the covering material, vacuum pressure in the biogas collection system, age of the cells, biogas chemical composition, etc. Further details, results and analysis will be presented in an upcoming blog.
For both landfills, the closed cells and flares represent significant odor sources. However, these point and surface sources have completely different dispersion patterns. A flare (high gas temperature & velocity) will have its maximum impact further away. A cell (near ambiant gas temperature & very low vertical velocity) will have its maximum impact very close to the source. Even at more than 1 km from the landfill, both types of sources will have an impact on ground level odor concentrations.
Candian Landfill Odor sources configurations:
French Landfill Odor sources configurations:
The following figures present the wind distribution patterns for both landfills.
These wind roses indicate the wind direction (TO) vectors (not the origin). As can be seen, the wind distributions are completely different for each meteorological data set, having a major influence on the modelled odor impacts.
The following figures present the modeling results for different scenarios and concentration frequency distributions. All contours express odor concentration (o.u./m3). Axis are in meters (positive Y axis for North & negative Y for South and, positive X axis for East & negative X for West).
The two following Figures present the levels at the 98th and 99.5th percentiles for the Canadian landfill and meteorological data.
The 98th Percentileconcentration distributions clearly follow the dominant wind pattern with an elliptical isocurve shape. The first agglomeration located at 3000 m North-East has low odour concentration levels, around 1 o.u./m3 at the 98th percentile. The 99.5th percentile isocurves are more distributed in circle shape pattern. The 99.5th percentile expresses the highest concentrations normally caused by low and calm wind conditions. Such calm winds typically occur in alldirections because they are not influenced by geotrophic winds than influence dominant winds.
The next two figures present 98th and 99.5th percentiles for the French landfill and meteorological data.
Consistent with the wind rose distribution, the impact distributions for the French landfill are very similar for 98th and 99.5th percentiles with concentric patterns. The concentrations at 3000 m are however higher than the concentrations of the Canadian landfill (up to 5 o.u../m3at the 98th percentile).
The sources and modeling comparisons allow the following conclusions to be drawn:
- The odor flow rates are comparable and consistent with buried waste volume
- The odor impact for the two modern large scale landfills are consistent and of the same order of magnitudes
- Extrapolations between landfills are not possible because many parameters influence the odor flux or odor concentration at each source. Site specific characterization will be necessary to have accurate odor impact evaluation for sensitive zone such as agglomerations
- Annual meteorological data distributions have a major influence on the 98th and 99.5th percentiles odor concentrations. This influence is very significant over 1000 meters from the sources, therefore specific landfill odor impact is very sensitive to local meteorological data.
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:
- Scientific planning,
- Experimental measurements,
- Evaluation of the impacts,
- Possibility of identifying some(s) tracer(s),
- 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)
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.
- The dominating odorous compound was H2S for all sites according to the odor threshold values retained for calculations.
- The analytical measurement of odorants consistently underestimated (by two orders of magnitude) the odor concentration compared to olfactometric measurements
- Poor correlation between odors and odorants concentrations
- Field values and emission factors of the AP-42 did not identify the same compounds as priority odorants.
- 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.
- 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.
- 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.
However, it has been scientifically demonstrated over the last decade that H2S is only partially responsible for the odors perceived offsite. Monitoring H2S for odor problems may lead to underestimations of the odor intensity or completely missing the contribution of other odorous compounds (VOCs, ammonia & amines, other sulfurous compounds, etc). We invite you to read these blogs:
Olfactometric quantification is essential for quantifying the overall odor level (odor concentration). Many operators today recognize the value of odor monitoring expressed in odor units for understanding odor complaints and improving their production processes. (http://blog.odotech.com/bid/51233/Pima-County-Marks-1-Year-of-Odor-Management-Innovation). However, there is a continuity problem in switching from H2S to Odor monitoring. How to relate the H2S historical data to the new Odor measurements ?
It is now possible to bridge the gap between H2S and Odor real-time monitoring by merging OdoWatch (odor monitoring with eNoses) with the new OdoSulf technology (H2S monitoring). Simultaneous H2S and Odor on the same platform is made easy with two 100% compatible technologies.
OdoSulf is the first automated system designed specifically for Hydrogen Sulfide (H2S) emissions with atmospheric dispersion plume display. The sulfNoses (H2S detectors) can measure H2S down to 2 ppb at the perimeter and up to 100 ppm at the emission source. The system delivers a real-time H2S atmospheric plume display. The data are then archived for future reference.
It is now possible with one air quality monitoring system to track real-time Odor and H2S. The eNoses and H2S monitors can be located at the sources and/or at the fenceline for the SulfNose. But all the sensors are integrated in one software to get H2S plumes and Odor plumes simultaneously and fenceline H2S logs. You can get alerted when odors are leaving your site, and know how far and were they travel.
Some of the possible uses of this combined H2S-Odor approach:
- Insure regulatory compliance (Track the H2S values at the property boundaries)
- Reduce the cost and impact of air quality & Odor investigations
- Improve community relations
- Monitor the effectiveness of abatement actions taken
- Optimize process
- Manage proactively
- Manage off-site impacts and complaints
- The sulfNoses + eNoses at the emission sources plus real-time modeling quickly determine whether or not the H2S from the facility is causing an off-site impact at complaint location
- In case of an alert, they show immediately which of the site sources needs action.
- Access historical data as needed.
- Monitor trends or address complaints.
- Quantify H2S/Odor to optimize H2S/Odor emission controls.
- Implementation of controls can be prioritized.