Versatile Bioreactor Design Reduces Cost: HRSD VIP Nutrient Reduction

The Hampton Roads Sanitation District (HRSD) in Virginia Beach, VA must upgrade several large wastewater treatment plants (WWTP) to reduce the mass of nutrients discharged to the Chesapeake Bay. HRSD operates thirteen wastewater treatment plants, seven of which operate under a bubble permit limiting the annual mass of total nitrogen (TN) and total phosphorus (TP) discharged into their common-pool receiving waters. This allows HRSD to economize upgrades to WWTPs that can maximize nutrient removal while minimizing the cost.The Virginia Initiative Plant (VIP) required upgrade to satisfy a phased decrease in annual mass discharge limits for nitrogen in HRSD's bubble permits for treatment plants in the James River watershed. The VIP currently provides seasonal nitrification, some denitrification, and enhanced biological phosphorus removal (EBPR) in the VIP process configuration with anaerobic, anoxic, and aerobic biological reactors. The project goals required reliably achieving 5 mg/l TN and 1 mg/l TP on an annual average basis. VIP receives high peak flows that challenge operating at higher mixed liquor suspended solids (MLSS) concentrations needed to maximize cold weather nitrification while preventing secondary clarifier solids washout.After evaluating several candidate process configurations, HRSD determined that a Versatile Bioreactor (VBR) following the existing VIP process maximized achieving process goals while minimizing cost. The VBR serves potentially in the following configurations:A fully anoxic denitrification reactor with potential external carbon addition to maximize denitrification during warmer temperatures when the original VIP reactor fully nitrifies.A partial aerobic/partial anoxic reactor during colder temperatures when the original VIP reactor struggles with nitrification to ensure complete nitrification occurs. Up to eight individual aeration zones can be configured to operate either aerobically or anoxically, maximizing nitrogen removal at all temperatures.A high-rate, fully-aerobic wet weather reactor parallel to the original VIP configuration capable of providing BOD removal treatment to flows that exceed the hydraulic capacity of the original VIP WWTP. Wet-weather parallel operations preserve the long-term nitrogen removal capability while sacrificing short-term nitrogen removal, a strategy frequently employed by WWTPs.Ammonia-based aeration control (ABAC) configuration in which both the VIP and VBR reactors operate at a typically decreased dissolved oxygen (DO) setpoint based upon the effluent ammonia from the reactor measured with an online sensor.VBR sizing considered site constraints, the VIP temperature histogram and the annual average discharge objective to maximize nutrient removal and minimize cost. The sizing and other operational analysis conducted for the Preliminary Engineering Report (PER) included developing several dynamic Biowin™ models to simulate operation during each of the configurations described above.This presentation describes the VIP VBR design evolution and the benefits of a VBR in providing cost-effective nutrient removal and wet weather treatment.