The La Crosse wastewater treatment plant will require up to $20 million in upgrades to meet Wisconsin water quality standards that go into effect in 2025, according to a preliminary phosphorus reduction plan by the city’s sewer utility.
The changes are intended to reduce by 90 percent the amount of phosphorus, a widespread source of aquatic pollution, in the city’s treated wastewater.
Phosphorus enters the environment from point sources, known sources of permitted wastes, and from pollution that runs off farms, fields, lawns, and parking lots. The La Crosse wastewater treatment plant is the largest point source of phosphorus pollution to the Mississippi River in Wisconsin, according to Jared Greeno, wastewater treatment plant superintendent.
An abundance of phosphorus in freshwater environments drives rampant algae growth that depletes oxygen levels in the water and lead to aquatic dead zones. Some blooms have a putrid smell and form floating mats that clog up the waterways. Others produce toxins that can contaminate drinking water and threaten public health in the form of rashes, nausea and vomiting, stomach cramps, diarrhea, muscle weakness, liver and kidney failure, and at high enough concentrations, respiratory paralysis leading to death.
Residential sources of phosphorus enter the La Crosse sewer system from human, animal and yard waste, and soaps and detergents. Wisconsin banned lawn fertilizers containing phosphorus in 2010; Minnesota has banned phosphorus in lawn fertilizer since 2005. Great Lakes Cheese, City Brewery and Kwik Trip Dairy are the primary contributors of phosphorus from industrial sources in La Crosse, according to a 2017 sewer utility report.
The La Crosse facility currently treats wastewater to limit phosphorus output to the Mississippi River to one milligram per liter, said Green. The facility does so using biological and chemical methods, which react with soluble phosphorus and convert it to a solid form that can be removed.
The $20 million investment would improve current processes and add a filtration system to remove non-reactive phosphorus. Without it, Greeno said, the city will not be able to comply with future standards of 0.1 milligram per liter.
Removed solids, which contain phosphorus, are applied to fields as fertilizer, Greeno said. The amount applied is determined by the nitrogen content in the solid waste. The state currently doesn’t limit the amount of solid treated waste that can be spread onto fields by phosphorus content, Greeno said.
The plan will be presented to the public, along with estimated rate changes, in March and April. The city must submit a final phosphorus reduction plan to the state by the beginning of 2020.
Jennifer Lu is the La Crosse Tribune environmental reporter. You can reach her by phone at 608-791-8217 and by email firstname.lastname@example.org.
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