Screenings removed from the wastewater are deposited in containers and ultimately hauled off-site for burial. The screened wastewater flows into two influent wet wells. A combination of three 150-horsepower influent pumps, using level controls, pumps the wastewater to the aerated grit chamber.

Grit is removed from the wastewater stream by a rolling action provided by the inlet hydraulics and a coarse bubble diffuser system. The wastewater then flows by gravity to two primary sedimentation basins. Each basin holds approximately 409,000 gallons and is equipped with chain and flight sludge collection mechanisms.

The non-metallic chains are driven by a low speed motor in each basin and each basin has a motor to provide power to a sludge hopper cross collector mechanism. In addition to scraping the bottom of the basin to bring settled solids to the sludge hopper in the front of the basin, the flights move along the water surface to collect scum and grease. The effluent from each of the basin flows by gravity to the aeration basins where it is combined with re-circulated activated sludge from the final clarifiers.

The function of the aeration basins is to remove oxygen consuming organic matter (pollutants) from the wastewater. This is done by supplying air to and maintaining a family of organisms (activated sludge) that decompose the pollutants. The two basins have an overall capacity of 3.86 million gallons and are supplied air by four 200-hp centrifugal blowers. The effluent from the aeration basin flows by gravity to the center wells of two final clarifiers.

 

The final clarifiers hold approximately 2.28 million gallons combined and are equipped with sludge and scum mechanisms.  The settled sludge in the clarifiers is either returned to the aeration basins or wasted out of the system. The effluent from the clarifiers flows by gravity to the chlorine contact tanks.

The function of the chlorination system is to supply chlorine to the treated effluent before it is discharged to the Androscoggin River. Chlorine is applied seasonally to the treated effluent to destroy disease causing (pathogenic) organisms and bacteria which may remain in the wastewater after the treatment process. The effluent is treated with sodium bisulfite to remove the chlorine, and then flows by gravity approximately 200 feet from the shore to a diffuser located in the Androscoggin River.

Excess (wasted) sludge is thickened and then sent to dewatering. The primary sludge is thickened using two primary thickeners, while the WAS (wasted activated sludge) is thickened using two gravity belt thickeners. The thickened sludge is then pumped to two belt filter press’s that dewater the solids to 18-22% solids.

 

The dewatered solids then either get lime added for land application, sent to the compost facility that is run by LAWPCA, or hauled to landfills.