Design Completion of Expansion Brings MSD Closer to Handling Increased Wet-Weather Flows

Source: 
Black & Veatch

Black & Veatch, a global engineering, construction and consulting company, has completed the design of an expansion for the Metropolitan St. Louis Sewer District (MSD) that will significantly increase the existing peak wet-weather treatment capacity of the Lemay Wastewater Treatment Plant. The project will benefit St. Louis residents not only by enabling MSD to effectively handle expected increases in flow over the next few years, but also by increasing the Lemay plant’s reliability and flexibility under a wide variety of operating scenarios. The expansion will ultimately improve the quality of wastewater discharges and make treatment more efficient.
Expansion of the existing wastewater pump station and 120-mgd WWTP, which receives flow from both separated and combined sewer systems, has been designed for an initial peak wet-weather treatment capacity of 340 mgd with provisions for expanding to an ultimate treatment capacity of more than 800 mgd.
“Utilities across the U.S. are challenged to find and implement wet-weather solutions that are both economical and effective,” said MSD Director of Operations Dave St. Pierre. “Careful consideration of our options and successful completion of the expansion design bring us closer to our goal of effectively managing the wet-weather flows we receive at our wastewater treatment plants.”
Wet-weather treatment options evaluated in a pre-design study and report completed by Black & Veatch in May 2004 included blending, chemically enhanced primary treatment (CEPT), ballasted flocculation, swirl concentrators, onsite storage facilities, and expansion of preliminary and primary treatment facilities. Additional grit removal facilities, primary clarifiers suitable for high-rate clarification such as CEPT and hydraulic controls comprise the first stage of an expansion that was also designed to accommodate future process modification and phased expansions.
According to Black & Veatch St. Louis Office Manager Tom Ratzki, location of a new outfall for the plant presented special challenges. For example, the project team had to route a 132-in.-diameter outfall across a major north-south railroad line and through a major casino and park development planned for the area between the treatment plant and the Mississippi River. Avoiding a conflict with a future interceptor tunnel planned by MSD similarly presented a planning and design challenge.
“Not only did we need to demonstrate close coordination with a number of agencies and parties involved in planning the development of the casino; but we also needed to be sensitive to the requirements of the railroad, plus coordinate with MSD’s own future plans. At times, all the parties’ needs conflicted, but in the end we agreed on an alternative that was both technically sound and met all parties’ basic needs,” said Ratzki.
The design also included a plant-wide HVAC system upgrade, odor control, and new piping and flow control between processes to allow flexibility between dry weather and wet-weather operations. The project is set to bid in early summer 2006.

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