Comparison of Odor Impacts from a Wastewater Treatment Plant Using the ISCST3 and AERMOD Dispersion Models

The U.S. Environmental Protection Agency (EPA) has approved the AERMOD dispersion model for use in demonstrating compliance with ambient air quality standards. This model replaces the Industrial Source Complex – Short Term model, Version 3 (ISCST3). The ISCST3 model has been the primary model used to estimate odor impacts from wastewater treatment plants. While the AERMOD model is described as being a new and improved model relative to the ISCST3 model, the predicted results for AERMOD may be higher than those predicted by ISCST3. The AERMOD dispersion model has not been used in odor impact assessments.The AERMOD model represents a significant improvement in the way a dispersion model characterizes the surface layer where most of the anthropogenic emissions occur. The AERMOD model also incorporates improved algorithms for the treatment of building cavity and wake effects and plume dispersion in terrain greater than the stack top elevation.This paper compares the predicted odor impacts from a Cincinnati wastewater treatment plant using the ISCST3 model to those predicted using AERMOD. The approach uses AERMOD to predict odor concentrations to determine whether the odor sources of primary concern and odor control recommendations are the same as those determined using the ISCST3 model. If the predicted odor impacts are significantly different for various classes of sources (point sources verses areas sources), a different odor control strategy may have been implemented. Further, the odor impacts from sources influenced by building cavity and wake effects or impacting elevated terrain features are examined to assess how the AERMOD characterized odor impacts from these sources. Odor impacts from open basins and lagoons will also be examined to assess how odor impacts from these sources differ from those predicted using ISCST3.The goal was to determine whether the odor control measures adopted at the plant based on the results of the ISCST3 model would have changed if the AERMOD model was used instead. If the odor impacts predicted by AERMOD were different from ISCST3, the factors contributing to this deviation were evaluated.