KCI provided design and bidding services for a new $300 million activated sludge plant, providing biological nutrient removal (BNR) level of treatment at the 180 million-gallon-per-day (MGD) capacity Back River Wastewater Treatment Plant. The proposed additional activated sludge facilities will supplement the BNR treatment currently provided by Activated Sludge Plants 2 and 3 which, with Project 1, will provide ENR level of treatment for the plant ultimate design flow. The new plant will include ABB PLC network expansions and integration with existing plant SCADA / HMI. The purpose for the project is to meet the nutrient reduction goals of the Chesapeake Bay Program together with any limitations associated with the imposition of Total Maximum Daily Load (TMDL) for discharges into Back River. Activated Sludge Plant 4 will include the following principal elements:
- Six activated sludge reactors, with a combined volume of 40 million gallons, in the MLE configuration. The reactors will incorporate swing zones, allowing for shift from anoxic to aerated operation, during high wet weather flow and cold temperature conditions, to maintain complete nitrification. Reactor anoxic and swing zones will be equipped with Invent® hybrerbolic mixers, for increased mixing coverage and energy efficiency. Reactors will include submersible internal mixed liquor recycle from the last aerated zone to the first anoxic zone, utilizing duplicate recycle pumps at each reactor with a capacity of 15,000 gallons per minute (gpm) each.
- A blower building, housing seven centrifugal blowers, each with VFD speed control, and with a capacity of 9,000 standard cubic feet per minute.
- Three sludge pump stations, for pumping RAS and WAS. Each sludge pump station will accommodate four secondary clarifiers, and will contain six RAS pumps with 5,000 gpm capacity each, three WAS pumps with 250 gpm capacity each, and two scum transfer pumps with 300 gpm capacity each.
- Twelve 120-feet diameter secondary clarifiers, with TowBro® clarifier sludge removal mechanisms and with a 150 gpm scum pump, in a scum well, at each secondary clarifier.