Challenge

Providing wastewater treatment services for 17 cities and counties in southeast Virginia, the Hampton Roads Sanitation District (HRSD) needed to upgrade capacity at the King William Wastewater Treatment Plant (WWTP) from 25,000 gallons per day (gpd) to 100,000 gpd. By 2006, the existing facility was used only to collect wastewater and not for treatment, causing $500,000 a year in hauling costs to transport the wastewater to a neighboring treatment facility.

With new development in the area, though, the plant had to be operational within nine months to comply with Virginia state regulations. This staged effort required a “turnkey” contract structure, whereby the equipment supplier-engineer-contractor team designed, procured and got the system up and running – then turned it over to HRSD.

Discharging into the Chesapeake Bay watershed, the plant had to abide by much stricter effluent nutrient limits due to the Water Quality Improvement Act of 1997, requiring advanced treatment technology. The solution also had to be portable for potential future plant relocation.

Solution

Based on a feasibility study and procurement process, the joint concept team of HRSD and Old Dominion University – collaborating for a winning submittal to the Virginia Water Environment Association design competition – chose the Siemens MBR Xpress™ package system as the optimal solution. The first of its kind to be completed in Virginia, the design combined ultrafilters with a biological process. The treatment train includes:

• Two self-contained 50,000-gpd membrane bioreactor (MBR) systems with five-stage biological nutrient removal, along with existing facility tankage (for equalization and sludge digestion).
• Varicant® jet aeration/mixing, which was picked due to significant turndown requirements because of the initial low flow and load variations.
• Chemical phosphorus removal to meet the stringent phosphorus limit (TP ≤ 0.3 mg/L), and a post-anoxic biological zone with supplemental carbon dosing to meet the stringent total nitrogen limit (TN ≤ 3 mg/L).
• A compact UV disinfection system that treats the filtrate to ensure coliform bacteria meets the permit requirements.

Results

The new King William plant was up and running within seven months of contract award, with initial flows between 10,000 gpd and 25,000 gpd. Even at this low flow, effluent nutrient levels have been well below permit limits. To date, the MBR system has shown it can perform well under very low loading conditions, and tolerate occasional variations in loading from commercial establishments in the service area. Moreover, the self-contained, plug-and-play MBR units allowed for easy installation and maximized integration of existing facility equipment in a limited footprint, while offering the desired portability, improving performance, and saving time and costs.