The processes at the Penacook Wastewater Treatment Plant provide secondary treatment capable of handling an average daily flow of 4.2 million gallons.
Raw wastewater is carried to the treatment plant by the collection system.
After receiving preliminary treatment consisting of screening, the wastewater enters the primary clarifiers for the removal settleable solids. The effluent from the primary clarifiers flows to the aeration tanks, biological treatment units which provide for the removal of dissolved and suspended organic material from the wastewater. The secondary clarifiers receive the overflow from the aeration tanks. These tanks separate the solids produced in the biological treatment processes from the wastewater, and send clarified effluent to the chlorine contact tanks for disinfection with sodium hypochlorite prior to discharge to the Merrimack River. Sludges, which are produced during treatment of the wastewater, are pumped to the gravity thickeners.