Sewage Treatment

Manchester underwent a major upgrading and expansion of its wastewater treatment plant from 1997 through 1999. The plant operates under the following EPA permitted flow limits:
  • 1.20 million gallons per day monthly average December through May
  • 0.67 million gallons per day monthly average June through November
  • 0.67 million gallons per day annual average (Ocean Sanctuaries Act Limit)

Raw Sewage enters the headworks building, passes through a “Muffin Monster” grinder and a grit removal cyclone before entering the influent wet well. Grit is separated from the raw sewage and is dewatered by a grit screw and accumulated for disposal. The raw sewage is pumped from the influent wet well to the aeration tanks where the biological treatment occurs. Sewage exiting the aeration tanks flows to two 48 foot diameter clarifiers where the sludge is settled out. Effluent from the clarifiers is chlorinated and discharged through the outfall pipe into outer Manchester Harbor.

Waste sludge from the clarifiers is accumulated in waste sludge holding tanks until sufficient volume is present to warrant operating the rotary drum thickener. The rotary drum thickener increases the percent solids of the sludge to approximately five (5) percent by removing excess water from the sludge. The thickened sludge is stored in a tank and then pumped into a tanker truck and transported to Upper Blackstone Water Pollution Abatement Facility in Millbury, MA for additional treatment.

The plant includes an odor control system that removes odors from the headworks building, the sludge holding tanks and the rotary drum thickener room using a negative pressure fan system. The odorous air is piped into a biofilter which uses a mixture of organic materials and biological action to remove the odors. The upgraded plant was designed to deal with the flow fluctuations we have historically observed. The plant is designed for an average daily flow of 1.2 million gallons, a maximum daily flow of 3.0 million gallons and an instantaneous flow of 5.0 million gallons. Although the plant is designed to treat 1.2 million gallons per day, the plant operates under an Ocean Sanctuaries Limit of 0.67 million gallons per day annual average which effectively limits expansion of the sewer collection system.