C+S June 2022 Vol. 8 Issue 6 (web)

Faced with an increase in extreme weather events, together with an increase in non-treatable solids such as “flushable” wipes, wastewa - ter treatment plants are under pressure to improve the resilience of their operations. As influent flows rise and fall, removing debris from headworks to prevent negative downstream effects can be especially challenging. To meet that challenge, the Saginaw (MI) Charter Town - ship Wastewater Treatment Plant (WWTP) turned to an innovative screening solution that offers a new level of adaptability to changing wastewater conditions. The challenge The Saginaw Charter Township WWTP has two headworks, one with two influent pipes of 21 and 36 inches, respectively; and another that serves the neighboring community of Thomas Township. The flows are combined prior to going through grit removal, primary treatment, oxidation and clarification. The system handles storm water runoff as well as sewage, resulting in dramatic increases in flows during periods of wet weather. “Our facility has a design flow of 4.65 million gallons per day (MGD). But when we have rain together with melting snow, we can peak at 20 MGD,” explains Saginaw Township Treatment Coordinator Tim Shepherd, noting that the storm system also brings lots of debris to the plant. “It’s amazing what finds its way into that stream. Everything from large chunks of wood and building materials to dead animals to trash and leaves.” This is in addition to the typical debris in the sanitary waste stream, including rags and grease. The solution To handle debris removal, the plant installed a Duperon FlexRake bar screen in 2002 with ½-inch openings at the headworks serving Thomas Township. In 2004, a 1-inch FlexRake was installed at the main head - works. This unit replaced an aging screen that required staff to manu - ally rake debris off it three times a day. In 2008, a second FlexRake was added to each headworks to provide screening redundancy. In 2020, the Saginaw Charter Township WWTP was offered the op - portunity to acquire an upgrade: a Duperon FlexRake IQ2™ that had been used for a pilot program in a nearby city. It features a new design that can adapt to ever changing flow conditions. Under normal operation, the unit has a ¼-inch openings for increased debris removal. During periods of high flow, the unit automatically adapts to the increased screen removal requirements by increasing the Duperon increases plant resilience with bar screen that adapts to changing flow conditions

speed of the raking system first. If speed alone does not satisfy the high flow conditions, the screen has the ability to then change the size of the openings to ¾-inch, handling up to 40 percent more flow. This increases hydraulic capacity during peak events to avoid bypassing the screens that would conventionally allow unscreened debris down - stream, creating maintenance headaches within the plant. The FlexRake IQ2™ was installed at the main headworks in August 2020, replacing the 1-inch FlexRake installed in 2004. Use of the new bar screen is alternated with the previously installed bar screen to keep both active. “But mostly we try to run the fine screen,” Shepherd notes. The results Once the FlexRake IQ2™ was in operation, it didn’t take long for plant operators to see the impact. “It was amazing how much more solids and grit it removed, which really helps out with everything downstream,” Shepherd says, noting that a fine grit accumulates in the rags and other debris and this is removed effectively by the FlexRake IQ2™. “This has really reduced the stress on the plant’s grit system.” Shepherd notes that the screen has removed roughly three times the amount of debris before it gets to the grit system. “Previously, we had



June 2022

Made with FlippingBook Annual report