Wastewater Treatment Plant


The South Hadley Wastewater Treatment Plant is an activated sludge, or secondary treatment, wastewater facility. The facility design capacity is 4.2 million gallons per day (MGD), with the limiting factor being the primary treatment tanks. The secondary portion of the plant, constructed between 1978 and 1980, has a design capacity of 5.1 MGD. The plant currently treats an average of 2.4 million gallons of sanitary wastewater per day, which includes wastewater from small portions of the neighboring communities of Chicopee and Granby.

Force Main

The plant flow enters the treatment plant through either a 16 inch or 24 inch force main which comes from the Main Street Pump Station. These pipes are located in the smaller tank and the water flow will then enter the Aerated Grit Chamber (AGC). The chamber uses fine bubbles to help settle out the sand (grit), which is mechanically removed with an auger into a one-ton dump truck, and disposed of at Chicopee Landfill. The fine bubbles also add oxygen to the water and help blow off sulfides.

Primary Clarifiers

The flow then travels by gravity to the 3 primary clarifiers, each sized for 122,400 gallons. Here the solids are settled out, and surface scum (fats, oil and grease) is skimmed off the top by plant personnel. The settled solids from this process are pumped 4-8 hours per day to the gravity thickeners for processing, and the scum will go to the Landfill.

Aeration Tanks

Next the flow enters the 4 Aeration tanks by gravity. The aeration tanks are 356,000 gallons each, and are designed to mechanically add oxygen to the wastewater, which is necessary for the bacteria to survive and consume the solids present in the wastewater. The number of tanks online depends on the plant flow. If the flow is low, only two tanks will be used, but under high flow conditions all 4 tanks will be online. The amount of oxygen added can now be controlled by varying the speed of the mechanical aerators by programming the SCADA System, which monitors the amount of dissolved oxygen (DO) in the system.

Secondary Clarifier Tanks

The process flow now proceeds by gravity flow into the 2, 340,000 gallon Secondary Clarifier Tanks, where the bacteria are settled out. Secondary scum is also skimmed off by plant staff. A percentage of the settled bacteria is pumped back into the aeration tanks to consume more solids, and the remainder is pumped into the gravity thickeners for processing. This process is described further on.

Chlorine Contact Chamber

The water then flows by gravity to the Chlorine Contact Chamber (CCC's) for disinfection. There are two sets of 4 chambers. As the water passes through, liquid sodium hypochlorite, which is 2.5 times stronger than bleach, is injected into the water. The lab technician routinely tests for coliforms, and monitors the chlorine residual in the effluent water.


The disinfected plant effluent then exits the treatment plant, tumbles down a cascade and enters the Connecticut River.

Gravity Thickeners

The solids from the primary and secondary clarifiers are pumped on a daily basis to 2 indoor tanks called Gravity Thickeners. These two55,000-gallon tanks are located inside the main operations building. The material settles by gravity and becomes thickened solids.


The thickened solids, or sludge, is then pumped to the belt press for final processing, called dewatering, which is done 2 or 4 times per week depending on operations. The sludge is thickened even more by the addition of a polymer. The material is slowly conveyed over the press, and water is removed from the material, resulting in what is called sludge cake. The sludge cake falls into a 30-yard dumpster, and the 15 tons of sludge cake is then sent to a sludge incinerator in Waterbury Connecticut final disposal.


View a slideshow of the treatment plant processes.

Contact Us

For additional information on the operations of a wastewater treatment plant or to schedule a tour, please email Mike Cijka. For additional information on treatment plant compliance or other programs covered under Water Pollution Control, please email Melissa LaBonte.