Enhancing Biological Nutrient Removal: Nansemond WWTP

Client: Hampton Roads Sanitation District
Location: Suffolk, VA

The Hampton Roads Sanitation District, in Suffolk, VA, needed to increase the capacity of its Nansemond WWTP from 10 to 30 mgd to accommodate its growing service area. HRSD also faced stricter standards for nutrient levels in the plant’s discharge as part of the Chesapeake Bay Act. HRSD retained Hazen and Sawyer to evaluate alternatives and design facilities for expanding the plant and achieving BNR goals.

Project Outcomes and Benefits

  • Designed a plant expansion and upgrade that meets a total nitrogen limit of 8 mg/L year-round and 1 mg/L total phosphorus year-round. This includes new supplemental carbon feed facilities capable of utilizing methanol, ethanol, glycerin, MicroC, corn syrup, or acetic acid.
  • Upgraded to provide sidestream treatment of centrate using the Ostara process and a backup ferric chloride addition system using an abandoned pretreatment structure to precipitate phosphorus and equalize the return stream.
  • The plant upgrade included improvements to hydraulic distribution channels, to further enhance process performance and ease of operation.
  • Upgraded the aeration system to include three separate dissolved oxygen control zones to optimize BNR and optimize supplemental carbon addition.

The supplemental carbon feed facility, seen here under construction, is capable of delivering glycerin, methanol, ethanol, acetic acid, and sugar water to the BNR process for enhanced denitrification.

Two new Turblex single-stage centrifugal blowers each with capacity of about 20,000 scfm were installed to meet the plant’s aeration needs for nitrification and BOD removal. These blowers replace two older smaller units to enhance the flexibility and reliability of the existing system.

One new GBT was installed in the solids processing building to enhance the flexibility of the NTP with regard to how solids are handled, thickened, and dewatered.

Two new BNR tanks were constructed to accommodate new nutrient removal requirements. All process tanks were equipped with a new Aquarius diffused aeration system that will feature three dissolved oxygen control zones to optimize nutrient removal utilizing dissolved oxygen meters, automated airflow valves, and a sophisticated air flow control strategy developed by Hazen and Sawyer.

One new nitrified recycle pump was installed to increase the capacity of the BNR system.

The Ostara process was implemented for side stream removal of phosphorus and nitrogen. The Ostara reactors and all associated equipment are housed in a new building, built specifically for the purpose. As part of the BNR upgrade, an old aerated grit channel and pretreatment tanks were repurposed for sidestream treatment and equalization as a backup to Ostara.

The BNR upgrade required an extending aeration volume into areas of the plant previously not aerated. As a result and to keep the existing aeration system in service while the improvements were built, a new section of aeration piping was installed. To avoid conflicts and keep walkways clear, this piping was elevated approximately 20 feet overhead.

Hazen and Sawyer designed the original 10-mgd plant, as well as its upgrade/expansion to 30-mgd, including addition of BNR, for the Hampton Roads Sanitation District.

Hazen and Sawyer has been involved with all of the major design and construction at the Nansemond Treatment Plant and recently designed biological nutrient removal (BNR) facilities such that the existing 30-mgd plant will meet an annual average total nitrogen of 8 mg/L. On previous projects, Hazen and Sawyer provided process evaluation, design, construction management and start-up services, O&M manuals and operator training for expanding and upgrading the Nansemond plant from 10 mgd secondary to 30 mgd.

Hazen and Sawyer provided the same basic services on the design of the original 10-mgd facility construction in the 1980s. The latest design provides for an advanced 5-stage BNR treatment process. The facility is designed to meet a total nitrogen limit of 8 mg/L, year-round. Chemical precipitation of phosphorus using ferric chloride was also incorporated into this design as a backup to ensure compliance with the required effluent limits.

Sidestream treatment of centrate is also included as a part of the latest upgrade. The sidestream treatment is primarily designed to remove phosphorus. One sidestream treatment option is the Ostara process, which will participate the phosphorus out as struvite pellets – marketed as slow release fertilizer.

The plant expansion also included hydraulic distribution channeling design features to enhance process performance and ease of operation. New and existing facilities were combined into a single process flow train. Equal flow and solids distribution under all flow conditions are provided.

Other features of the design include new screening, grit, primary settling, final settling, and chlorination/dechlorination facilities. Sludge handling facilities include gravity belt thickeners, high solids centrifuges, and truck loading facilities. The preliminary engineering included wetlands delineation, environmental assessments, and securing all Federal, State and local permits.

Considerable process flexibility was incorporated into the BNR facility design. The plant can operate in 3-stage mode in the winter to avoid unnecessary additional construction, VIP mode, 5-stage BNR + VIP mode, and 5-stage BNR mode. There is also the flexibility to change process conditions, such as internal recycle flows and vary the anaerobic, anoxic, and aerobic mass fractions.

For more information on this project, or to discuss a similar project in your area, contact

Robert DiFiore, P.E. at rdifiore@hazenandsawyer.com