Odor Scan Evaluation of a Composting Facility
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 profile 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 windows 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…