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La Crosse wastewater plant upgrades meet strict phosphorus limit; cogen start planned for March 5
Summary
Public works staff said upgrades at the La Crosse wastewater treatment plant — including disc filters, enhanced digesters and a heat dryer — are meeting a 0.1 mg/L phosphorus limit; staff estimated chemical costs near $1 million annually and said the plant's cogeneration unit should run 24/7 after a direct-transfer switch is installed by March 5.
Jared, the wastewater superintendent, briefed the Board of Public Works on Jan. 12 about the multi-year upgrade to La Crosse’s wastewater treatment plant, saying the project has improved reliability, created energy-recovery opportunities and achieved a new low-level phosphorus discharge limit.
The plant treats about 10 million gallons per day (10 MGD) with a biological-oxygen-demand load of roughly 30,000 pounds per day. As part of the upgrade, staff installed fine screening, new disc filters and expanded digester capacity. Jared told the board the disc filters are meeting the current phosphorus limit — about 0.1 milligrams per liter — but that doing so drives maintenance and chemical costs. He said the plant uses roughly 500 gallons per day of ferric chloride and estimated the annual chemical expense at approximately $1 million.
Jared summarized flood-risk work and asset protection after the board asked whether the plant should be relocated. He said an estimate to move the plant to higher ground was about $440 million, so the project instead focused on flood protection measures such as stop logs and bypass pumping at high river stages.
The upgrades also incorporated redundancy (transformers and switchgear), QR-code tagging for equipment maintenance and an expanded anaerobic-digester complex with improved mixing and thermal control. Those changes increase methane production, which the city plans to use in a combined heat-and-power (cogen) engine to produce electricity and recover heat. Jared said the cogen unit was commissioned in early 2024 but could not be run 100% until the utility direct-transfer switch work with Xcel Energy was completed; staff expect that switch to be installed and the plant to begin 24/7 cogen operation on March 5.
A new heat dryer reduces the volume of biosolids dramatically, Jared said: what previously required thousands of semi-trailer loads can be reduced substantially once drying and handling are routine; the operation creates a drier, potentially marketable Class A biosolids product, although staff are still working on odor control and any required certifications for widespread marketing. Jared also confirmed the plant continues to accept high-strength hauled waste only from its service area and is cautious about taking trucked waste from outside the area because of PFAS and other contaminant concerns.
Board members asked for a plain-language explanation of the biological treatment processes used to remove phosphorus and nitrogen; Jared described aeration and microbial processes and referenced routine operator tests such as a 30-minute settleability check to monitor system health.
Why it matters: the upgrades put La Crosse’s treatment plant in position to meet stricter effluent limits, reduce haul volumes for biosolids and lower operational risk through redundancy and on-site power generation. The scale of chemical and maintenance costs, the cogen commissioning date and ongoing odor-control work on the dryer are operational items that affect rates, budgets and project planning.
Next steps: staff will finalize commissioning steps for the cogen unit, continue optimization of the dryer and complete planned lift-station and interceptor lining projects through 2027–28.
