Air Dispersion Modeling at Wastewater Plants: A Significant Shift in Odor Objectives

Engineers have used air dispersion modeling for many years to determine offsite odor impacts from wastewater facilities. The recent use of the European standard to measure odor concentration has resulted in significantly higher emission rates being measured and, because they are directly proportional to emission rates, higher offsite impacts being projected.Goals and regulations established based on the previous American standards are no longer valid if the new European standard is used. Plants with uncontrolled area sources comprising open tanks, channels, and basins should have great difficulty achieving single-digit odor unit impact goals unless there is a significant perimeter buffer.Offsite impacts predicted by the three most commonly used models are generally highest for CALPUFF, second highest for ISCST3, and lowest for AERMOD. The AERMOD model became the U.S. Environmental Protection Agency preferred steady-state model in 2006. This paper is not intended to be a comparison of dispersion models.Measures that can be implemented to reduce offsite impacts from area sources include construction of barrier walls, use of wind machines to break up stagnant air, and good operational practices.