Wastewater from Allenstown and Pembroke enters into the Headworks, which screens out large items and removes grit
Then it flows to the aeration tanks. This step is called the Biological Treatment. Air is added to the aeration tanks to maintain an abundance of various bacteria that breaks down the organic wastes.
The liquid is received from the aeration tanks into the clarifiers (known as secondary settling) where the bio-solids settle out and are either pumped to a holding tank to be processed through the dewatering system or pumped to the beginning of the biological treatment. The clear liquid on the top overflows into the weirs and is sent to disinfection.
The clear water sent from the clarifiers is treated with chlorine to destroy any e-coli bacteria and any other harmful bacteria. This treated water is then sent to the Merrimack River.
The bio-solids that settled out from the clarifiers is sent to our screw press. The press is used to remove water from the bio-solids in order to reduce transportation and disposal costs. The water that is removed ends up back in the aeration tanks.