School Wastewater Treatment Facility Design

Develop Alternatives and Design a Wastewater Treatment Facility for the Middlesex School

Weston & Sampson was selected by the Middlesex  School in Concord, Massachusetts, to develop alternatives and design a wastewater treatment facility (WWTF) upgrade to replace aging equipment. The school entered into an Administrative Consent Order (ACO) with the Commonwealth for  the upgrade, which was concurrent with the issuance of a new, more stringent National Pollutant Discharge Elimination System permit. 

The ACO included explicit milestones for completion of design, permitting, and construction. The schedule required the submittal of final design documents within 100 calendar days, with construction starting immediately after permit procurement.

The upgrade design was confined by minimal expansion area at the site and the need to keep the existing treatment process in operation. Incorporating existing features of the WWTF and creative process retrofitting allowed the objectives to be accomplished without compromising cost or effectiveness.

The WWTF design is based on the membrane biological reactor (MBR) microfiltration technology that uses anoxic and aerobic processes prior to membrane filtration and ultraviolet disinfection.  The membranes allow the process to employ far greater MLSS concentrations than conventional activated sludge, resulting in lower capital and energy costs and reduced solids generation. Influent screening and multiple chemical feed systems are also integral to operation.

Since the MBR technology systems are proprietary, the school had to negotiate the purchase of the MBR system prior to bidding and construction, which compressed the schedule even further.

The WWTF is designed to treat the average daily flow of 60,000 gallons per day, while handling peak daily flows in excess of 120,000 gallons per day.  Peak flow conditions are accommodated with a flow equalization tank and the use of variable speed pumping units for additional energy savings.

The WWTF is also designed to meet BOD and TSS limits of 10 mg/l, and seasonal ammonia and total phosphorous nutrient limitations of 1 mg/l and 0.2 mg/l, respectively.  The technology allows for beneficial reuse of WWTF effluent, which provides the school with future disposal options in lieu of surface water discharge.

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