Odor generation and impact on the surrounding communities is a significant issue facing existing and proposed composting facilities. Left unchecked, odor impacts can lead to a facility shut down. Odor modeling can be used to evaluate alternative operating methods, siting options and
odor control technologies by calculating projected impacts on the surrounding community and demonstrating compliance with regulatory and community odor restrictions prior to facility siting and construction. The City of Boulder, Colorado is in the process of developing biosolids dewatering
and composting facilities to generate a Class A biosolids product. Conceptual layouts for three (3) alternative composting processes including agitated bed, aerated static pile, and modified tunnel were developed and evaluated. Each facility layout was sized to process 12 dry tons per day
of dewatered biosolids on a 5-day per week basis. An odor evaluation was performed for a specific site using the United States Environmental Protection Agency (USEPA) recommended Industrial Source Complex Short Term (ISCST3) air dispersion model to quantify the potential odor impact on the
surrounding community resulting from the three (3) alternative facility configurations. The analysis used a ten-minute duration odor peaking factor based on published values. In all three alternative configurations, emissions from active mixing, composting, and curing processes were assumed
to be collected and treated by biofiltration odor control system(s) before release to the atmosphere. Five (5) years of local meteorological data were used to cover a wide range of atmospheric conditions. The meteorological and local topographical data was used to determine the overall
dispersion of the odor plume. In addition, specific receptor locations were selected to represent the nearest (most sensitive) receptors. A five (5) square kilometer area surrounding the facility was modeled with twelve individual receptor locations examined for off-site odor impacts. According
to the general provisions of the Colorado Air Quality Control Commission, Regulation No. 2: Odor Emissions, the odor standard for areas used predominately for residential or commercial purposes states “…it is a violation if odors are detected after the odorous air has been diluted
with seven (7) or more volumes of odor free air.” at the facility boundary. For purposes of this evaluation, an odor concentration at a receptor located outside the facility property line exceeding seven (7) D/T was considered an odor impact. The evaluation indicated that all three
(3) facility configurations were comparable resulting in minimal offsite odor impacts. Additional analysis concluded that modifying odor control system locations and layouts significantly affected the overall odor impact resulting from each of the facility configurations. The impact of layout
modifications on predicted off-site odor impacts is presented.
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