Old School No Longer

Oct. 9, 2003
Membrane bioreactor modernizes wastewater treatment facility at boarding school

About the author: Thomas C. Schwartz is a project manager for Woodard & Curran. For further information, phone 207/774-2112.

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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.

Effluent areas

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, substantial upgrade.

"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 Academy.

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.

Retrofit activated

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 1994-retrofitted facility.

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.

System successful

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 bacteria.

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.

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