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Helping a wastewater plant handle heavy demand

The upgraded grit facilities will ensure that the Central Treatment Plant remains resilient in the face of extreme weather and heavy demand.


The Middlesex County Utilities Authority (MCUA) was created in 1950, with the mission of preserving and protecting the environment of the Raritan River and Raritan Bay. In the 1970s, the MCUA built the Edward J. Patten Water Reclamation Center in Sayreville, a formerly important river port named for the owner of a company that manufactured bricks from local clay.

With five pump stations and nearly 140 miles (225 kilometers) of sewer line serving it, this secondary treatment plant uses a pure oxygen-activated sludge process and has a capacity of 132 million gallons per day (MGD). It includes an aerated grit settling facility, primary sedimentation tanks, oxygenation tanks, and final clarification.

The original aerated grit facility consisted of three settling tanks, each with a rated capacity of 100 MGD. During extreme wet weather, periods of high flow, or when one tank was out of service for degritting, the grit facility could not effectively meet the demand. Grit would pass through and accumulate in the primary sedimentation tanks.


In 2009, MCUA retained Mott MacDonald to design a fourth aerated grit tank. The design included the following:

  • Reinforced concrete foundations, walls, and baffles
  • Isolation sluice gate
  • Segmented stop gates
  • New aeration piping and diffuser system
  • New serpentine overflow weir

The design addressed process considerations to allow the necessary grit settling and removal, modifications to the influent and effluent channels, and provisions for a future fifth grit tank. Mott MacDonald also designed an extension of the railway on which the degritting crane travels.


Built at a construction cost of $2.1 million, the fourth grit tank was structurally tied to the existing concrete structure while the third tank was in service. We worked closely with MCUA so that construction would have a minimal impact on plant operations.

The upgraded grit facilities will ensure that the Central Treatment Plant remains resilient in the face of extreme weather and heavy demand.

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