Membrane bioreactor modernizes wastewater treatment facility at boarding school
When the country's oldest private boarding school had to
upgrade and modernize its wastewater treatment facility, it employed a new and
innovative technology to resolve an administrative consent order (ACO) to bring
itself into compliance and avoid the possibility of paying hefty fines.
Gov. Dummer Academy, named after former Massachusetts Gov.
William Dummer who served at lieutenant governor from 1716 to 1723 and governor
from 1723 to1728, was founded in 1763 in Byfield, Mass., approximately 33 miles
north of Boston.
For the academic year 2003-2004, roughly 370 students from
the U.S. and 12 other countries live on campus, as do a majority of the 110
faculty members and their families.
The academy's wastewater treatment facility was built on
site in the 1960s as the campus infrastructure evolved from the single
schoolhouse to the present complex of over 40 buildings and after tests showed
site soils could not accommodate subsurface disposal.
Even with a retrofit in 1994, the wastewater facility could not
consistently meet the effluent quality required by its permit. Frequent pump
outs of the clarifier and the aeration tank by tanker truck were necessary to
keep the system functioning even at a minimal level.
So, in 1998, the Massachusetts Department of Environmental
Protection (MDEP) and the Academy agreed to an ACO, requiring a quick,
"To complicate matters, the site is located in forested
wetlands, meaning additional land would not be available for
modifications," said Richard P. Savage, chief financial officer for the
In addition to being surrounded by wetlands on three sides,
a steep hill is located on the fourth. The Academy's forested wetlands location
has been designated an Area of Critical Environmental Concern by the
Commonwealth of Massachusetts. The estuary and the freshwater streams where the
treated effluent is discharged are ecologically sensitive areas that include
clam flats and fishing and recreational areas. The effluent enters a stream
that flows into the Parker River, which runs to the Atlantic Ocean. This area
is also frequented by tourists. For these reasons, the effluent discharge
permit is extremely stringent.
The Academy's Savage retained Woodard & Curran, an
environmental engineering, science and operations firm to upgrade, modernize
and operate the wastewater treatment facility. The firm quickly determined that
the actual peak flows were about four times the capability of the
Furthermore, without a complete replacement of the existing
system, the flows and loads could not be managed, nor the National Pollution
Discharge Elimination System permit requirements met. Alternatives considered
ranged from packaged units to sequencing batch reactors. When the possibility
of membrane bioreactor technology was presented, its appropriateness was clear.
Jim Fitch, P.E., vice president with Woodard & Curran,
led the design effort, and said, "The membrane bioreactor option would
allow retrofitting of existing treatment tanks to provide the needed capacity
without constructing additional tanks or other concrete components."
The Academy and the MDEP both endorsed the plan, and design
and construction proceeded on a fast track. The facility was shut down, and the
retrofit of the treatment tanks was completed and brought online in 41/2 days.
All work was completed 21/2 months before the ACO deadline.
The new system separates treated effluent from the mixed
liquor (biomass) solids using hollow fiber microfiltration membranes. These
membranes are submerged in the aeration tanks and permeate is drawn across the
membrane using a vacuum pump. The membranes allow the purified water to pass
through, while creating a complete barrier to the passage of any solid greater
than 0.4 microns, which includes all mixed liquor solids and most coliform
The mixed liquor's suspended solids in the tank, the heart
of the activated sludge system, can be operated at levels up to six times
higher than conventional systems. The biomass is removed directly from the
aeration tank using a submersible pump. The waste sludge is then stored in an
aerated storage tank and periodically allowed to settle and decant to increase
sludge concentration. Combined with the higher mixed liquor solids the process
permits, the management of solids becomes more efficient, while allowing for
greater treatment capacity.
Membrane bioreactor technology replaces a conventional
system's secondary classifiers. The elimination of secondary clarification
reduces labor, operation, and maintenance costs. The mixed liquor/suspended
solids concentration runs at 8,000 to 12,000 mg/l achieving treatment in a much
smaller tank volume compared to traditional treatment applications.
The system is monitored by a Supervisory Control and Data
Acquisition system that Woodard & Curran engineered to monitor and log data
24 hours a day, seven days a week.
The system notifies personnel of alarm conditions both
onsite and remotely. It also allows staff to dial in and monitor operating
conditions, and collects data for documentation purposes.
Today, the effluent is consistently below discharge license
limits. Whole effluent toxicity testing is performed four times a year and the
facility has consistently met these license limits.
In addition, it is producing 20% less sludge than a
conventional treatment facility. After being sent through ultraviolet
disinfection, the Academy can, and does, safely and confidently discharge to
the Parker River watershed.