WSSC Energy Conservation Measures Design-Build


WSSC Energy Conservation Measures Design-Build


WSSC Energy Conservation Measures Design-Build


WSSC Energy Conservation Measures Design-Build


WSSC Energy Conservation Measures Design-Build


WSSC Energy Conservation Measures Design-Build



Washington Suburban Sanitary Commission

Energy Conservation Measures Design-Build

Accokeek, Upper Marlboro,

& Laurel Maryland

Contract: $6,600,000

Design-Build Team Members
Owner: Washington Suburban Sanitary Commission, Laurel, MD
Design-Builder: Constellation Energy Source
Design-Build Engineer: Rummel Klepper & Kahl

Design-Build Contractor: Johnston Construction Company

Key Accomplishments:

  • Johnston Construction Company worked in partnership with the Washington Suburban Sanitary Commission (WSSC), Constellation Energy Source, and Rummel, Klepper & Kahl (RK&K) for construction of the multi-million dollar Energy Conservation Measures (ECM) implemented at three WSSC wastewater treatment plant (WWTP) locations in Maryland.
  • The resulting operational cost savings from the constructed ECM at each plant will be used by WSSC to payback Constellation Energy Source financing for the project.
  • Construction of other plant improvements will result in the reduction of chemical, operational, and maintenance expenses.

Project Description:

Johnston Construction Company, in a parallel design-build contractor relationship with the design-build engineer, provided engineering, construction, and project commissioning services under a fixed price contract to implement 5 Energy Conservation Measures (ECMs) at three waste water treatment plants. The total contact value for all 5 ECMs was $6,600,000.

The ECM project was implemented at the WSSC Parkway WWTP, Western Branch WWTP and Piscataway WWTP. ECM development and implementation followed several steps. RK&K would develop a preliminary design concept with estimated construction costs and operational savings. The next step involved RK&K and Constellation Energy Source presenting the concept to WSSC. If WSSC requested further development, RK&K and Johnston Construction Company developed a preliminary design, construction cost estimates, plus methods to measure and verify operational savings. Following final negotiations with WSSC and Constellation Energy Source, RK&K and Johnston Construction Company completed the design and started construction using design-build delivery methods.

At the Parkway WWTP, the ECM construction included: replacement of coarse-bubble diffusers with Sanitaire® 9”ф membrane disc fine bubble diffusers and associated aeration equipment improvements; and, upgrading the solids handling facilities. The diffuser replacement included a new 300 Hp Hoffman blower to improve the range of airflow with new dissolved oxygen sensors, flow meters and air control valves to improve aeration control. The second ECM at Parkway improved the solids handling system. The existing solids handling equipment was inadequate for lime/sludge mixing with a Putzmeister pump, a pebble lime delivery system and plow blenders. New solids handling equipment included a pug mill, solids and powdered lime conveyors, and a solids storage bin. These improvements will result in the existing centrifuge operating at its design capacity and to produce a drier sludge cake that will reduce the solids volume and associated hauling costs. Converting from the use of pebble lime to powdered lime will improve mixing and reduce the quantity of lime that is purchased and hauled for disposal.

The Piscataway WWTP ECM included the replacement of liquid rheostats with variable-frequency drives on the influent pumps. Reduced energy consumption will result from this improvement along with the alleviation of operational and maintenance problems encountered with the prior control system.

Construction of the Parkway WWTP ECM portion of the project is near completion with the Western Branch WWTP ECM project completed in August of 2005 and the Piscataway WWTP ECM project completed in January of 2005.