Large-Scale Oxygen Injection for Odor Control at Primary Clarifiers at the Trinity River Authority of Texas

The Trinity River Authority of Texas owns and operates the 162-MGD Central Regional Wastewater Treatment Plant in Grand Prairie, Texas. The plant is an advanced secondary facility consistently producing nitrified effluent with BOD and TSS concentrations less than 5 mg/L each and an ammonia nitrogen concentration less than 0.5 mg/L. In addition to providing high quality effluent, the Authority is committed to being a good neighbor to the commercial, recreational, and residential areas surrounding the plant. As such, the Authority has committed significant funds and manpower to minimize the emission of odors from the plant.In projects spanning more than 20 years, the plant has eliminated or minimized emissions from major odor sources such as the preliminary treatment areas, influent junction boxes, primary clarifier weirs, and sludge processing areas. The plant eliminated use of its sludge-only landfill except for screenings and implemented beneficial reuse of all its sludge. The next phase of odor control would include the management of odors from aerated grit units and the quiescent areas of the primary clarifiers. Covering the primary clarifiers could involve literally acres of covers and the collection and treatment of well over 150,000 cfm of foul air.As an alternative to the covering of the primary clarifiers and collection and treatment of the air, the Authority, with Alan Plummer Associates, Inc., conducted “full-scale pilot studies” to investigate the feasibility of using pure oxygen for odor control. Pure oxygen has been used for odor control in pressure lines in collection systems and in receiving streams to boost oxygen concentrations during critical low-flow periods. Use of pure oxygen for odor control at a wastewater treatment plant, however, is a new application.Following the success of the pilot study, the Authority conducted a second bench-scale study to identify optimum dosage rates and injection points. This study identified the reaction rate of sulfide oxidation for the wastewater stream and provided a basis of design. The system began operation in June 2007. Following startup, the Authority conducted performance testing to identify the reduction in hydrogen sulfide, reduced sulfide, total odor (dilution to threshold) and other parameters.