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Nuisance odors are a complex and subjective issue, often resulting in odor complaints directed at industrial or agricultural facilities such as wastewater treatment plants, landfills, large scale composting facilities, or animal feed operations. At these types of facilities, most odorous chemical compounds are produced under anaerobic conditions. Contrary to popular belief, nuisance odors themselves do not generally cause long term illness or any direct health effect.  In other words, if the source of the odor is taken away, any associated illness symptoms (e.g. nausea) will also go away. Therefore, unlike investigations centered on human health risk, investigations involving nuisance odor are governed by the perception of the receptor. A person’s perception of odor is related to the human olfactory system, which can vary widely from person to person; what smells bad to one person might not have an odor at all to someone else. To further confuse the issue, there is a distinct lack of odor regulations, and those that exist are extremely vague. The EPA defaults to the state level for nuisance odors, and most states defer to the county or local level.

Odor is a parameter which may be measured unto itself, following established ASTM and/or European Standards. This approach will quantify how odorous a sample is, ranking it on a relative scale with units of dilution to threshold (D/T).

Knowing the magnitude of an odor problem is useful, but often more detailed chemical information is necessary when odor control engineering solutions are being evaluated.  When a detailed chemical analysis of odorous compounds is needed, there are several analytical options:

1. Produced during the acidogenesis stage of anaerobic digestion, reduced sulfur compounds have a very characteristic odor of rotten eggs, rotten garlic/cabbage, skunk or natural gas. In fact, the human nose is sometimes more sensitive than the most current analytical instrumentation used to detect these compounds. An example of these compounds is methyl mercaptan, which has an extremely low odor threshold (this is why mercaptans are used as natural gas odorants). The most popular analytical option for reduced sulfur compounds is ASTM Method D5504. This method quantifies a list of 20 speciated reduced sulfur compounds (such as hydrogen sulfide, mercaptans, thiophenes) using gas chromatography with a sulfur chemiluminescence detector (GC/SCD).

2. With a characteristic fishy/fertilizer or putrid/sour/pungent odor, amines are the result of the biological breakdown of amino acids and are produced at various stages of anaerobic digestion. Columbia Analytical has developed a comprehensive amine sampling and analytical method that reports a list of 13 amine compounds with reporting limits at or below published odor threshold concentrations. A sample is collected on an in-house designed sorbent tube using a personal sampling pump. Due to their unique chemical characteristics, amines will not always be detected in any of the other tests described here (e.g. VOC test). Analysis of the samples is via a specially modified gas chromatography with nitrogen phosphorous detection (GC/NPD).

3. Ammonia, which is produced by microbial decomposition of animal waste, has a characteristic odor most people will recognize due to the compound’s use in window cleaners. At higher concentrations, ammonia can cause serious health damage, irritating and/or burning nasal passages and lungs. Collection of airborne ammonia may follow the OSHA ID-188 method, which uses sulfuric acid-coated Anasorb-747 (carbon bead) tubes and a personal sampling pump for collection. This means of sample collection is much easier and safer than the traditional collection technique of sulfuric acid solution impingers. Analysis may follow the OSHA-ID 164 analysis, which utilizes an ion-specific electrode (ISE) to detect ammonia.

4. Carboxylic (volatile fatty) acids are produced as a result of the biological anaerobic breakdown of proteins, with typical odor characteristics including a rancid, fecal, vomitous, or sweaty gym sock smell. Columbia Analytical has developed a comprehensive sampling and analytical method that reports a list of 15 carboxylic acid compounds with reporting limits at or below published odor threshold concentrations. The sample is collected on a sodium hydroxide-treated silica gel tube using a personal sampling pump; the subsequent sample is then analyzed via gas chromatography/mass spectrometry (GC/MS).

5. Several other analytical methods may be used to quantify levels of aldehydes and other miscellaneous volatile organic compounds (VOCs). EPA Method TO-11A (silica gel tubes coated with acidified 2,4-dinitrophenylhydrazine (DNPH) ) is an appropriate method for sampling of aldehydes (carbonyl compounds).  EPA Methods TO-15 (stainless steel canisters) and TO-17 (thermal desorption tubes) are appropriate methods for sampling of volatile organic compounds.  Polar volatile compounds such as alcohols, aldehydes, esters, ketones, ethers, phenols and cresols are often contributors to nuisance odors.

Due to their complex nature, there is no “one size fits all” approach for evaluating the chemical composition of odors. Odorous compounds may have additive, synergistic or antagonistic effects, all contributing to odor perception. Multiple analytical methods or evaluation approaches may be required to address a single source.

Learn more about Odor Testing…

Columbia Analytical recently conducted a field evaluation of Odor Scan, a suite of methods that has been designed to address compounds that have very low odor thresholds and are irritating at low levels. The suite consists of sampling and analytical methods for carboxylic acids (volatile organic/fatty acids), amines, reduced sulfur compounds and odorous volatile organic compounds (VOCs) such as microbial volatile organic compounds (MVOCs), and high molecular weight aldehydes and alcohols. Two of these methods (ie. amines, carboxylic acids) were developed and validated by Columbia Analytical.

The study was conducted to evaluate the new methods under field conditions and to collect data to profi le the airborne contaminants and odors associated with a composting facility. Due to the wide range of compounds anticipated and the fact that some analyte overlap exists among the methods, this sampling event was also used to compare sampling and analytical methods and sampling media.

The facility composts a variety of materials including green waste, cow manure, construction materials (e.g., sheet rock), and chicken and fish waste. The compost was piled in seven uncovered windrows that were located outdoors on a concrete slab. At this facility, the composting process takes approximately six to seven weeks from the time the material is received until it is ready for screening. Heavy equipment called a SCAT is used to turn the material in the windrows, which helps aerate the product, an important component of the composting process. The final compost product generated is sold for landscaping.

Air samples were collected at the property’s fence line, on top of compost piles and on the SCAT used to turn the compost piles. Sampling media, fl ow rates and analytical methodologies utilized are summarized in Table 1. Calibrated personal sampling pumps were used to collect the solid sorbent samples. For some target compounds (e.g., VOCs, reduced sulfurs), collocated samples were collected using more than one media type.

The analysis of samples for tentatively identifi ed compounds (TICs) by EPA TO-15 and NIOSH 2549 was achieved by comparing the mass spectra of the selected peaks with those from the NIST library, which contains spectra from more than 120,000 compounds. The concentrations of TICs were estimated by comparing the peak area of the compound with that of the nearest internal standard. As the compounds present at the highest concentrations are often not the odorous ones, the analysis was not limited to the 15 largest peaks, as is often the case with these methods. Instead, for method validation purposes, all those peaks with suffi cient response to permit identifi cation of the mass spectra were selected. In some cases, it was not possible to locate the peaks buried in the complex matrix. For some compounds (e.g., carboxylic acids), it was diffi cult to accurately estimate peak area because of the wedge shape of the peaks produced using the EPA and NIOSH methods. The Columbia Analytical Carboxylic Acid method resolves this problem.

Approximately 350 different compounds were identifi ed during the study, including many of the reduced sulfur, carboxylic acid and amine compounds on the OdorScan target lists as well as a diverse mixture of VOCs. Trimethylamine was the predominant amine, while acetic, butyric, propionic and isovaleric acids were the principal carboxylic acids found in many of the samples. When the two VOC methods (NIOSH 2549, EPA TO-15) were compared, more substances were detected in the samples collected on thermal desorption tubes (265 compounds) than in Silco canisters (219 compounds). The types of VOCs identifi ed included higher molecular weight alcohols, aldehydes and ketones (e.g., 2-heptanol, decanal, 2-octanone), terpenes (α & β-pinene, d-limonene, carene), furans, phenols and cresols. Microbial volatile organic compounds were also detected in several of the samples.

As expected, the highest levels were observed in the samples collected near the source: at the top of the compost piles and during the turning of the compost. Samples collected from the newer piles tended to be more complex with respect to the VOCs and reduced sulfur compounds

detected. Based on comparisons with reported odor thresholds, butyric acid, valeric acid, isovaleric acid, acetic acid, propionoic acid, isobutyric acid, dimethyl disulfi de, acetaldehyde, decanal, nonanal, benzaldehyde and, p-cresol were likely contributors to the odor detected at the edge of the property. The preponderance of carboxylic acids present at levels above their odor thresholds was consistent with the sweaty/fecal/sour odor detected.

Although the NIOSH 2549 Method detected the greatest number of compounds, it did not appear to be an effective technique for identifying the presence of amines. The method also underestimated carboxylic acid levels. This study suggests that even a fairly comprehensive method, such as NIOSH 2549, does not effectively capture the full range of compounds that may be contributing to a complex contaminant matrix. The use of the four different methods that comprise OdorScan was a better choice for characterizing the airborne contaminants associated with this odorous source.

Read more about Odor Investigations…

Read more about Odor Compounds at a Compost Facility (PDF)…

Read more about Odor Testing…