Water Environment Federation (WEF)

Dispersion Modeling as a Tool to Establish Odor Policy

Odor control is a critical component of the Orange County Sanitation District’s (the Sanitation District) planning and operations. The Sanitation District’s two wastewater treatment plants (Fountain Valley, CA and Huntington Beach, CA) were isolated when originally constructed in the middle of the 20th century, but are now surrounded by high-density residential areas as well as highly used recreational areas, such as Huntington Beach and the Santa Ana River Trail. The Sanitation District has made odor control a top priority for some time and continues to improve upon their excellent record to avoid odor impacts on the surrounding community.

The Sanitation District is currently embarking on a program to upgrade and expand many of their foul air treatment systems to provide a higher level of foul air capture and improved treatment facilities. Additionally new odor control systems are being designed with the Sanitation District’s new secondary treatment systems and new biosolids thickening and dewatering systems. The original basis for these odor control designs was the Sanitation District’s Odor Control Master Plan (OCMP), completed in 2002. The OCMP based dispersion modeling on hydrogen sulfide (H2S) equivalents and recommended odor control measures to reduce H2S emissions to minimize their odor impacts in the neighboring residential and recreational areas.

The Sanitation District later became concerned that planning for odor control in terms of H2S equivalents was not suitable for the wide range of odor sources at the plants. While H2S is the dominant odorant from the influent headworks and primary treatment processes, other odorants, such as reduced sulfur compounds (RSCs), ammonia and amines become more dominant from residuals processing facilities. Based on these concerns, the Sanitation District embarked on a supplemental odor modeling effort based on odor units in terms of dilutions to threshold (D/T) to
provide a more comprehensive assessment of odors throughout the two treatment plants.

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