The City of Manchester, N.H., owns and operates a 42-million-gallon-per-day wastewater treatment facility under its Environmental Protection Division (EPD).
The facility, located at 300 Winston St., was originally constructed in 1975. To handle its primary clarification and gravity thickening processes, the facility was outfitted with three 130-foot-diameter primary clarifiers and three 50-foot diameter gravity thickeners. These settling tanks and their internal steel components had been in service for more than 40 years, with the exception of one primary clarifier and one gravity thickener that were added in 1993.
Underwood Engineers’ Primary Clarifier and Gravity Thickener Upgrade of the Manchester, N.H., wastewater treatment facility concluded successfully last fall. (Photos courtesy of Underwood Engineers, Inc., Concord, N.H.)
Several years ago, the three primary clarifiers and gravity thickeners were still performing acceptably; however, the internal steel components were deteriorated and had reached the end of their useful life.
In June 2015, the EPD selected Underwood Engineers to provide engineering design and construction services to upgrade the internal components of all primary clarifier and gravity thickener tanks. A construction contract was signed with Methuen Construction in the fall of 2016, with a total project cost of $9 million.
Project highlights included replacement of the internal components of the clarifiers and thickeners with stainless steel, as well as custom-designed odor control covers for the indoor gravity thickeners; interchangeable drive units for the clarifiers and thickeners; new thickened sludge pumps; new thickened and primary scum pumps; miscellaneous valve and piping upgrades, and pre-and-post-construction performance testing.
The Primary Clarifier and Gravity Thickener Upgrade project concluded in fall of 2018, and provided the City’s wastewater treatment facility with new equipment that will last another 40 years.
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