A Multi-Faceted Approach to Odor Control for a 28.5-Mile Long Force Main
- Kristen L. Smeby, P.E., David S. Ehrhardt, P.E., Brian F. Duane, P.E. – Hazen and Sawyer, P.C.
The Eastside Conveyance System consists of a 28.5-mile long wastewater force main with 3 constant speed pumping stations and 2 in-line booster pumping stations. The force main travels over hilly terrain and includes of numerous air release valve locations. Given 153 possible operating scenarios, a multi-faceted approach to address odors along this force main was required, including:
Hydraulic Modeling/Surge Analysis: The system was modeled using a steady-state hydraulic model and a transient (surge) model. The results showed that many ARVs could be permanently closed along the force main and identified improvements that minimized the air release volumes and pressures at the remaining ARVs.
Hydraulic models further showed that odors at ARVs could be minimized by boosting the hydraulic grade in the force main to prevent the pipeline from draining. These included two modulating valves, a 37-foot tall standpipe with gooseneck and a surge relief tank at each pumping station to prevent a vacuum condition. System changes minimized the odor problems but did not eliminate odors entirely.
Foul Air Capture and Treatment: A vapor phase odor control system was provided at each pump station wetwell to minimize odor complaints and at one ARV location. Two emergency odor control systems were also required prior to construction completion.
Chemical Addition: The County had a long history of Bioxide feed at wastewater pumping stations, however Bioxide was not effective due to the long retention time in this system. A switch to Magnesium Hydroxide provided positive results for this system.
Different aspects of the modeling, surge analysis, foul air treatment, chemical addition and mechanical/hydraulic changes discussed above were implemented for this system effectively. The County’s experience with the implementation of these techniques will be shared, including a discussion of which applications worked best and which were problematic.
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