The Broad Run Water Reclamation Facility (BRWRF; Ashburn, Va.) is on the cutting edge of new technology for wastewater treatment and reuse. It is so new that the operators are still cleaning construction dust from breakers. The 41,600-m3/d (11-mgd) facility has a computerized brain, a membrane bioreactor (MBR) at its heart, and a team of operators for its soul.
Loudoun Water (Ashburn), a water and wastewater authority supported solely by ratepayers, owns and operates the facility. Staff members at other Loudoun Water facilities have dubbed BRWRF the “push-button” plant because of its extensive supervisory control and data acquisition system. The plant is fully automated and could be operated from a remote facility, if needed.
However, as operations supervisor Michael Rumke said, “the bugs don’t read the books, and sometimes humans have to step up to the challenge.”
The liquids treatment process consists of preliminary and primary treatment, biological treatment with biological nutrient removal in an MBR, granular activated carbon treatment, disinfection, and post-aeration. Effluent is discharged to Broad Run, which ultimately flows to the Potomac River and Chesapeake Bay.
BRWRF is required to meet stringent requirements, because its discharge is located upstream of a drinking water intake on the Potomac River. In addition to flow from the local collection system, the facility also treats a limited amount of septage hauled in from unsewered parts of the surrounding area.
At first, the septage-receiving holding tank was accumulating grit in the bottom and creating blockages in the suction and discharge lines of the transfer pump. The grit also was causing excessive wear on the pump’s stator.
To fix this problem, the maintenance staff installed a 1.5-m (5-ft) standpipe in the bottom of the tank to enable grit to accumulate without passing through the suction line to the pump. Now, the grit is captured in the holding tank and pumped out monthly.
Preliminary and primary treatment consists of influent screening (6 mm), grit removal using vortex grit separators, primary clarifiers, and fine screening (2 mm). This section of BRWRF includes multiple addition points for sodium hydroxide (for alkalinity and pH control), as well as polymer and alum or ferric chloride (to aid suspended solids and phosphorus removal). Preliminary and primary treatments are designed for a hydraulic peaking factor of 2.5.
Downstream facilities are designed for a hydraulic peaking factor of 1.88. To accommodate flows in excess of the 1.88 peaking factor — this is an instantaneous flow of 68,130 m3/d (18 mgd) — BRWRF uses two 18.9-million L (5-million gal) equalization tanks. When influent flow drops, the equalization tanks are drained back to the influent pump station.
The equalization basins help maintain a consistent flow through the facility. The consistent flow, coupled with the fact that BRWRF is running at only half capacity, gives operators some flexibility running equipment and swapping out tanks.
The biological treatment process is a five-stage MBR, consisting of an anaerobic zone, an anoxic zone, an aerobic zone, a second anoxic zone, and a final aerobic/membrane zone. Immersed membranes provide the liquids/solids separation function. The biological reactor basins can be operated in multiple treatment modes by reconfiguring the various recycle streams.
The five-stage process, as well as more addition points for methanol and alum, enable the facility to meet its strict nutrient limits — 4 mg/L for total nitrogen, 0.1 mg/L for total phosphorus, and 1.0 mg/L for total Kjeldahl nitrogen. The facility also has a 10-mg/L limit for chemical oxygen demand.
The facility’s MBR process and technology involve much ancillary and supporting equipment, along with subprocesses, to produce high-quality effluent.
For example, one area of concern was the formation of thick foam on top of the biological reactor basins. The maintenance and operations staff resolved this issue by installing a system that sprays chlorinated (sodium hypochlorite) water on the foam. The spray itself knocks down the foam, and the chlorine helps kill foam-causing bacteria.
Following membrane filtration, the permeate is pumped to two permeate storage tanks. From the tanks, permeate flows by gravity to six granular activated carbon contactors that BRWRF uses to remove dissolved organic materials that the membranes cannot filter out.
Finally, the flow receives ultraviolet disinfection and reaeration before being discharged into Broad Run or pumped to reuse.
As the plant equipment came on-line, the operators worked closely with vendors to understand the technology, operation, and control of the membrane technology. The staff cited vendor support and training as critical to the operators’ success in providing a high-quality effluent for the environment.
Loudoun Water offers effluent from BRWRF for nonpotable reuse. The first water-reuse project is to install 1200 m (3900 ft) of 400-mm (16-in.) “purple pipe” for a water-reuse main to serve a private office building and the “One Loudoun” World Trade Center development. The second project is to install 1500 m (4920 ft) of purple pipe to reach the National Rural Utilities Cooperative Finance Corp. (Herndon, Va.) facility. Both customers expressed interest in receiving reclaimed water for irrigation, cooling towers, and other nonpotable uses to help meet the criteria for LEED (Leadership in Environmental and Energy Design) certification as designated by the U.S. Green Building Council (Washington, D.C.).
The key to all of BRWRF’s success lies in its staff, even though many of them began as strangers to each other. When the plant went on-line in March 2008, the staff had never worked together before. However, they soon turned this circumstance into an asset.
The staff included both rookies and veteran operators with more than 20 years of experience. Led by shift supervisors Frank Stokes Jr., Albert Owens Jr., Eugene Wharton, and David Gray — four of the best in the business, according to Rumke — everyone pulled together to form a good team. Operators who were proficient in certain sections of the plant shared information with the rest of the team. Veteran operators helped younger operators to prep for their certification exams. Now, the team is starting to “gel” and land on the same page regardless of the operational or mechanical issues that may arise, Rumke said.
©2011 Water Environment Federation. All rights reserved.