Wastewater treatment plant performance must produce an effluent (the water discharged to the river) that meets all of the quality criteria as specified in the WPDES permit. One of those criteria specifies the concentration of effluent phosphorus.
Phosphorus is a nutrient which accumulates in the environment and can show-up as algae blooms on the surface of rivers and other water systems. In Wisconsin, measures to reduce the amount of phosphorus entering waterways from point sources (essentially, pipes discharging to these water systems) are imposed on cities through issuance of WPDES permits related to both treatment systems and Municipal Separate Storm Sewer Systems (MS4s).
There is extensive information regarding phosphorus and phosphorus-related issues affecting Wisconsin’s water systems on DNR’s website.
Prior to the current WPDES permit, the effluent phosphorus limit for the City’s wastewater plant was 1.4 mg/l, based on a monthly average. With the issuance of the current (2016 through 2020) permit, not only was the limit for effluent phosphorus reduced to 1.0 mg/l, but the permit also includes specific requirements and a compliance schedule for facility planning to eventually meet an effluent phosphorus limit of 0.1 mg/l. Working with an engineering consultant, the Utility has started the process of reviewing and evaluating options for meeting this much-lower water quality standard.
Additional information will become available as the Utility works through this process.