Wastewater Treatment Facilities and Process

Collection System - There are 21 pump stations in the collection system, which discharge to the main pump station on James Street. All flow passes through grinders as it is lifted into the WWTC.

Grit Removal - There are two parallel aerated grit tanks with a detention time of approximately 24 minutes at average daily flow (9 minutes at peak day flow).

Screenings - There are two parallel manually cleaned coarse bar racks (screens) with an automatic bypass.

Primary Settling - There are three primary clarifiers (two 22 m dia. and one 18.2 m dia.). The two larger primary clarifiers are manufactured by Dorr-Oliver and the third primary clarifier, which features a circular mechanism in a square tank, was manufactured by Westech. The original primary clarifiers were converted into a final clarifier and an equalization tank and one was abandoned. Primary sludge is pumped directly to the anaerobic digesters.

Activated Sludge Tanks - The original basins were installed in 1947 and consisted of four cells. In 1990, the process was expanded by adding two more cells. The six cells operate as a single plug flow reactor. Aeration is provided by full floor coverage of tube type pore diffusers.

Secondary Clarifiers - There are five secondary clarifiers - two round (30.5 m dia.) and three square (two 12.7 m square and one 16.7 m square).

Return Activated Sludge (RAS) - There are three RAS pumps that pull suction from a common wet well. The pumps are operated with variable frequency drives to maintain a level in the wet well. There is a flow meter on the RAS line.

Waste Activated Sludge (WAS) - WAS is controlled by a gate valve on the RAS line and is sent directly to an equalization (EQ) tank which is aerated (previously a primary clarifier). From the EQ tank, the WAS is pumped to the dissolved air flotation (DAF) thickener. From the DAF, the thickened WAS is pumped to the primary digester.

UV Disinfection - There are two banks of UV modules used for effluent disinfection. There is an actuated weir gate to control the level in the UV channels. Flow from the UV continues to the outfall.

Anaerobic Digestion: Sludge is stabilized in a two-step anaerobic digestion process. The secondary digester has a floating cover for gas storage. The boilers are dual-fired and excess gas is flared. Digested sludge is sent to one of two lagoons where it is stored prior to being hauled to local farms for land application. Digested sludge is land applied in the spring and then again in the fall after the harvest.