The Hampton Roads Sanitation District (HRSD), which provides wastewater treatment services for 17 cities and counties in southeast Virginia, owns and operates the King William Wastewater Treatment Plant (WWTP) near Richmond, Va. Effluent from the original 25,000 gpd activated-sludge package plant emptied into the Pamunkey River. In 2006, the existing facility was used only to collect wastewater and not for treatment, resulting in the district hauling the wastewater to a neighboring wastewater-treatment facility at a cost of $500,000 annually (approximately $1,500 daily).

With new development in the area, the plant needed to expand to an estimated 100,000 gpd and be operational within nine months to comply with Virginia state regulations. As such, the project required a “turnkey” contract structure, meaning the equipment supplier-engineer-contractor team would need to design, procure and set up the system, get it running, and then turn it over to HRSD.

The plant also had to discharge into the Chesapeake Bay watershed and, as a result, needed to abide by much stricter nitrogen and phosphorus effluent limits established by the Water Quality Improvement Act of 1997. Due to the discharge location, an advanced treatment technology was required to meet stringent effluent nutrient limits for total nitrogen (TN) of 3 mg/L and total phosphorus (TP) of 0.3 mg/L.

The plant flow and loading was expected to be extremely low initially as only a small number of residents and commercial establishments would be connected to the plant. However the permit limits were still in force during this period so the ability to operate the system at a rate as low as 13 percent of design and still achieve required nutrient limits was a high priority.

Finally, in addition to operating over a wide range of influent conditions, the selected solution also needed to provide a consistent high-quality effluent and be operated simply and efficiently. It also needed to be cost-effective and portable for potential future plant relocation.

One Solution Meets Demands
“Our retrofit solution had to meet a wide variety of needs,” recalls Dr. Jim Pyne, small communities division chief at HRSD. “To help us hit upon the right solution, we [HRSD] collaborated with Old Dominion University based on their winning submittal from the VWEW (Virginia Water Environment Association) design competition.”

The joint concept team conducted a feasibility study of membrane bioreactor (MBR) technology. Study results proved that a MBR system would be the best solution to implement at King William. Additional findings indicated that using MBR technology would eliminate many of the treatment problems associated with gravity separation used at other older HRSD package plants, making operations more robust and reliable.

Through a procurement process that included soliciting proposals, it was determined that the Siemens MBR Xpress™ package system was the optimal solution based on three factors: use of existing facilities, treatment performance, and portability. The plant could be installed quickly as the Xpress units were pre-assembled, wired and tested in the factory before shipment. Siemens teamed with Heyward Incorporated, Mid Eastern Builders, Inc., and Reid Engineering Co. in a design-build contract. While the treatment skids were being built in the factory, site work was completed. So when the units were finally delivered onsite, minimal work was needed to get the system up and running.

The King William WWTP was the first of its kind to be completed in Virginia, combining microfiltration membranes with a biological process to produce a superior-quality effluent meeting low-nutrient standards. Two self-contained 50,000 gpd MBR systems with five-stage biological nutrient removal were used along with existing facility tankage (for equalization and sludge digestion). Each MBR unit was set up as an independent process train, allowing for flexibility to treat low initial flows with one train and providing a high level of redundancy for ease of maintenance and process assurance.

Varicant^® jet aeration/mixing was also selected for the design, due to significant turndown requirements because of the initial low flow and load variations. The jet aerators allow the operator to mix the process tanks while limiting the aeration air supply (during low flow). Jet aerators also eliminate in-tank diffusers and the need to periodically drain the tanks for diffuser maintenance.

In addition, the King William MBR system includes chemical phosphorus removal to meet the stringent phosphorus limit (TP ≤ 0.3 mg/L), and incorporates a ­post-anoxic biological zone with supplemental carbon dosing to meet the stringent total ­nitrogen limit (TN ≤ 3 mg/L).

Lastly, a compact UV ­disinfection system treats the ­filtrate to ensure coliform bacteria meet the permit ­requirements.

Retrofit Benefits
The new King William plant was up and running within seven months of contract award with a flow between 10,000 and 25,000 gpd. Even at this low flow, the effluent nutrient levels have been well below the permit limits. To date, the MBR system has shown that it can perform well under very low loading conditions and can 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, saving time and costs. The design also offered relatively simple ­construction as well as easy operation. Project documents allowed proposals that helped control material costs. ­Regulatory review and approval of ­procurement documents (in place of ­conventional Preliminary Engineering Report documents) expedited the review process and improved project timing and construction costs.

Use of membrane filtration ­technology has also allowed HRSD to greatly improve performance and ­increase capacity at the existing site, with the ability to meet future flows of up to 100,000 gpd.

“The process is producing an extremely high-quality effluent that is helping to protect the environment and quality of life in King William County,” concludes Pyne. SLDT

About the authors: Todd Heintz is the chief operator for the Hampton Roads Sanitary District (HRSD) in Virginia Beach, Virginia. He can be reached at 804-843-2582 or at This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
John Irwin, P.E. is a technical sales manager for MBR technology at Siemens Water Technologies. He is located in Ann Arbor, Michigan and can be reached at 734-995-1283 or at This e-mail address is being protected from spam bots, you need JavaScript enabled to view it