History - Waste Water
Prior to 1940, the City of Stevens Point had no sewage treatment facilities. Raw sewage discharged directly to the Wisconsin River via three outfall sewers. The original treatment plant was put into operation in 1940. Plans for the treatment plant were prompted by a State order requiring all sanitary sewage to receive primary treatment. The City acting with foresight, elected to build a complete treatment plant because they felt secondary treatment would be a future requirement.
As a result of a survey started in 1953, a major addition was made to the treatment plant in 1963. This addition consisted of adding two additional aeration tanks and a blower building, and replacing the mechanical aerators with compressed air aeration. During this major expansion many minor upgrades were made. Two variable speed raw sewage pumps having a maximum capacity of 3,000 gpm replaced a 500 gpm and 1,000 gpm pump. Also, a piston sludge pump was installed along with two digested sludge lagoons.
Another addition was made to the treatment plant in 1972. The modifications primarily consisted of two comminuters, a bar screen, additional raw sewage pumping capacity, two primary settling tanks, two aeration tanks with two new blowers, a clarifier, a chlorine contact tank and chlorination building, three new Return Activated Sludge (RAS) pumps, a sludge division box, conversion of one existing primary tank to a waste sludge thickener, one new digester, and one new sludge lagoon.
Beginning in 1992, the treatment plant was reconstructed again. The new design eliminated old technology and incorporated new, more modern technologies. The comminutors were replaced by mechanically cleaned bar screens. Chlorine disinfection was eliminated and replaced by Ultraviolet (UV) disinfection. Grit removal was added to reduce wear and tear on pumps and associated equipment. Sludge storage lagoons were replaced by more environmentally friendly, sludge storage tanks.
In 1997, the activated sludge system was modified to facilitate enhanced biological phosphorus removal (BPR). The new activated sludge operation utilizes the anaerobic/oxic (A/O) process which incorporates biological phosphorus removal into our original activated sludge system.
A series of improvements beginning in 2003 were implemented to address plant efficiency and energy conservation. These improvements started with new grit removal and fine screening equipment which handle the incoming solids more effectively. Also, two 50 hp plant air compressors were replaced with one 15 hp unit which uses much less electricity. In addition, two 15 hp channel aeration blowers were shut down and replaced by new piping to utilize excess process air. Further, anaerobic digester sludge thickener efficiency was increased by installing supplemental heating of polymer dilution water and equipment that increased mixing for more effective dispersal of the polymers. Also, a water to water heat exchanger was installed to allow methane generated hot water to be utilized to heat 3 buildings. Additionally, a heat pump is now being used to tap into the heat and cooling available from our effluent water. This is used to heat and cool our lab and office building.