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The Oconomowoc Wastewater Treatment Facility lies in the rolling countryside of western Waukesha County in the southwest corner of the City of Oconomowoc. The activated sludge facility has been online since June 1977 when it replaced the original plant that dated back to 1935. Hydraulic design parameters for the facility are 4.0 million gallons per day average flow and 9.0 million gallons per day peak flow. Organically, the facility is designed for 8,340 lbs/day of biological oxygen demand (BOD) and 6,672 lbs./day of suspended solids (SS). The present population served by the facility is equivalent to approximately 16,000. Current effluent limits of 10 mg/l for BOD and SS have been in effect since the facility began treating wastewater in 1977.

Effluent from the Oconomowoc Facility is consistently within permit with BOD and SS typically maintained below 5 mg/l and 2 mg/l respectively. Although not a requirement, the facility consistently nitrifies ammonia to a level below 0.4 mg/l. Upgrades to the facility include fine bubble aeration in 1989, gravity sludge thickening and sludge storage in 1990, dechlorination in 1994, filtrate storage and handling in 1995, and fine screens in 2001.

Oconomowoc's facility is unusual in that although it has reached its design life, loading is only at approximately 60%. The physical plant is in excellent condition, giving tribute to the exceptional maintenance it has received since construction.

The Oconomowoc Wastewater Utility is part of the City's Utility Department that also consists of water and electric service. The Utilities SCADA System provides monitoring and control for the utilities and a GIS system is utilized for system mapping. The Utilities are managed in a proactive manner, incorporating 10-year Capital Improvement Plan, 10-year Replacement Fund Plan, commercial and industrial monitoring, and comprehensive safety programs. The efficient operation of the Oconomowoc Utilities is reflected in user rates that are near the lowest in the area.

• The facility treats all wastewater generated by residential, commercial and industrial property in Oconomowoc as well as serving five sanitary districts and the Okauchee Lake area.

• The wastewater is treated by eight major processes or steps. These include: screening and pumping, grit removal, primary settling, activated sludge, secondary settling, filtration, disinfections and oxygen uptake.

• The treatment process is a continuous, ongoing sequence of steps which operates 24 hours/day, 365 days/year.

• The activated sludge treatment step is one of the most significant steps in the treatment process. The process utilizes concentrated microorganisms in a natural environment to convert pollutants in the wastewater to biomass. The biomass is continually returned to the process to maintain the treatment process.

• Wastewater sludge, the byproduct of the treatment process, is processed to reduce volume in a three step system, including air floatation thickening, anaerobic digestion, and gravity thickening.

• In the sludge digestion process, an average of 15,000 cubic feet of methane gas is produced daily and utilized to offset natural gas use for heating of the process and plant buildings.

• After the processing of sludge is complete, the nutrient rich, stabilized byproduct is transported to area farms where it is incorporated into the crop land for soil enrichment and fertilization.

• Very few chemicals, at minimal volumes, are used in the process.

• Over 17 billion gallons have been treated since the plant was put on line in June, 1977.

• The average daily volume treated at the plant is 2.3 million gallons.

• The maximum daily volume treated was 6.937 million gallons on April 20, 1993.

• The wastewater collection system contains 73.5 miles of sewer main ranging in size from 8" to 60" in diameter, and fifteen pump stations located throughout the City for pumping wastewater from low areas.

• The facility and collection system is monitored 24 hours per day, 7 days per week, 365 days per year, through the use of modern computer systems.

• The WTF contains an on-site laboratory where extensive daily testing of wastewater from various treatment stages is conducted.

• The Wastewater Treatment Facility is used as a research center and has hosted visiting engineers and municipal officials from all over the world.