Chemical Analysis in Odour investigations
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:
- 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).
- 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).
- 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 impinges. Analysis may follow the OSHA-ID 164 analysis, which utilizes an ion-specific electrode (ISE) to detect ammonia.
- 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).
- 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.