An Odor Attribution Study to Determine the Relative Contribution from Three Closely Located Facilities

An Odor Attribution Study was undertaken for an Air Quality Management Agency that included gathering extensive data from specific sources and ambient locations to better understand odor impacts within the local communities. The study was 'one-of-a-kind' in that it combined multiple innovative techniques for identifying fingerprint odorants attributed to specific odor generating facilities. Odor has historically been an issue in this area for decades. Over the years, various odor mitigation approaches have been undertaken with varying degrees of success. While the number of odor complaints from residents has decreased in recent years from a peak of 3,500 in 2015, the high number of complaints (1,500) reported in 2018 indicates a persistent and ongoing odor issue. The odors in the area originate primarily from three closely located facilities including: -Facility A: An Anaerobic Organic Material Digestion Facility -Facility B: A Solid Waste Resource Recovery Park (a recycling facility, a composting facility, and a landfill) -Facility C: A Water Resource Recovery Facility (WRRF) Other natural sources were also considered (e.g.; bay, estuary). The goals of the project were to determine the contribution and variability of odor causing compounds from these facilities and develop a strategy for measuring how often and at what concentration these potential odor causing compounds may be passing into the local community. The study approach went beyond using the traditional, common practice of using odor threshold or odor intensity as the measure of odor nuisance. Instead, Weber-Fechner (persistency) curves were used as part of the Odor Profile Method (OPM) developed by Dr. Mel Suffet of the University of California-Los Angeles. The usefulness of the OPM lies in the fact that the human nose is, for the most important odorants, many degrees more sensitive than the standard chemical compound identification analytical methodologies. Examples of the OPM results are shown in Figure 1 and illustrate the odor intensity reduction with dilution (persistency curves) as well as the character of the dominate type of odors at each dilution (e.g.; musty, rancid, sweet). This illustrates how odor intensity and odor character changes as it travels from the different odor sources into the community, demonstrating the 'peeling the onion' phenomenon. The OPM approach was combined with comprehensive chemical compound identification analyses, lab olfactometric analyses, field olfactometry sampling, as well as a proton-transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) to provide targeted measurements of specific VOCs to identify chemical fingerprints associated with the different sources. Comprehensive chemical compound analyses resulted in the following key findings in terms of fingerprint odorant types attributed to each facility: -Facility A - Anaerobic Organic Material Digestion Facility: Sweet, Rancid, Musty -Facility B - Solid Waste Resource Recovery Park: Rancid, Sweet, Sulfur -Facility C - WRRF: Sulfur, Decaying Vegetables The field surveys using field olfactometers were undertaken on a regular basis over a period of 18 months. Figure 2 shows a BLOB map of the likely odor impacts in the community and the contributions to the odor intensity from each facility based on the odor character descriptions during the in-field odor olfactometric assessments. The PTR-TOF-MS provided real-time (1/sec) 'chemical fingerprints' of over 550 tracked compounds and showed that the plumes from each facility were unique for the key odor sources at the facilities and that the contribution of each facility could be quantified. Plumes and/or odors in the communities were also collected. The plume data (concentration and ratio between individual species) were then fed into Sartorius Multivariate Analysis (MVA) software to determine correlations between facility plumes and community plumes. The data correlations were determined using Principle Component Analysis (PCA) which identified where plumes within the communities originated, including the facility releasing them. It also confirmed the results that were obtained using the in-field olfactometric analyses, the OPM analyses, and the lab chemical analyses as well as the lab olfactometric analyses that the odor signature is unique for each facility. The findings provided a solid basis for developing a method to employ ongoing monitoring along each facility's fence line, or at other locations in the community. The preferred monitoring system would include multiple sensors, weather station, data processing and visualization platform, and auto bag sampler (at community locations). The autosampler would fill a bag sample for remote analysis by proton-transfer reaction (PTR). This successful study provided an improved understanding of the relative contribution of odor causing compounds from the three adjacent facilities by assigning specific fingerprint odorants to each and provided insight as to how the unique odorants impact the local community. These findings are considered essential to better: 1.Inform future actions to reduce odors (best practices, enforcement, rules) 2.Establish methods to measure progress on facilities' future odor reduction actions 3.Educate the community in terms of what's causing the odors, how complex they are, and teach them how to characterize odorants to better inform ongoing improvement efforts.