The history of La Crosse’s wastewater treatment plant is written in its buildings, from the 1936 front door to the brick building next to the Mississippi River where searing ultraviolet light kill off bacteria. That’s the final step in the treatment process.
It’s a process that first extracts debris — such as socks and cellphones — and then produces sand, methane and fertilizer for farm fields.
“Different plants definitely have their own personality,” Mark Johnson, city of La Crosse utility manager, said. “Depending on the design, they can have different features, different styles. I think this plant is a little bit unique because you’ll see different generations of additions as you go through it as compared to some cases they pretty much throw away the old and build a new one.”
The plant built in 1936 replaced the practice of discharging from the sewer lines — the first of which were built in the 1880s — directly into the Mississippi River. Its two rectangular primary clarifiers are still available for use today.
When it was constructed it was alone on the Isle de Plume.
“They portrayed it as a city park,” Jared Greeno, wastewater treatment general superintendent, said.
The plant is between Houska Park and a marina. It has an expansive view of the Mississippi, nice in the warmer months. It also makes it easy to visualize the plant’s grounds used as a park area in 1936 when it was first built.
A newspaper article announcing its open house on July 9-10, 1938, said residents and businesses donated items for the park — a flag pole, bubbler, sun dial, bird bath, flower urns, lumber of benches, a birdhouse and spruce trees — “that can be fittingly set out and in future years decorated at Christmas time.”
“The plat and grounds have been improved to a great extent in the 10 months it has been in operation. There is still considerable work to be done on the grounds, but already the city has a pretty little park surrounding the building,” the article said.
That building’s architecture used marble in the entryway, and heavy wood doors with windows inside, which remain in use today. The original cabinetry also remains in the lab, although it has been refinished.
The original plant cost $500,000. General contractor Theodore J. Molzahn and Sons Inc. began construction Sept. 8, 1936. It was operational by Aug. 31, 1937.
The sewage treatment process in its beginning would only be a few steps into today’s process. The 1936 plant removed solids, chlorinated the water and sent it into the Mississippi.
Today’s process is much more intense as it begins by mechanically straining out debris — stuff that should not be flushed such as socks, Legos and flushable wipes that really are not flushable, Johnson said.
The city has 204 miles of sanitary sewer mains and 26 lift stations. But not all of the 10.5 million gallons of effluent a day that comes to the plant is from La Crosse. Effluent also comes from La Crescent, Onalaska, and the towns of Shelby and Campbell.
The debris from that first filtering, on average, fills a six-ton dump truck each week, Greeno said. That goes into the county landfill.
The process separates solids and suspended solids using large concrete pools called clarifiers. The solids settle to the bottom while the water flows on through the system. That water is biologically treated by encouraging bacteria to feed. It passes through another clarifier and then through ultraviolet light treatment before being sent out.
A total of 18 hours elapses from the time a drop of water enters the plant to when it is discharged to the Mississippi, Greeno said.
Along the way, sand is separated and sent to the landfill where it is used to cover garbage.
The biological waste extracted from the water makes its way to anaerobic digesters. In those 18-foot deep, circular concrete-walled structures, the waste is broken down by bacteria, and enough methane is produced to lift a lid made of steel, concrete and rubber. It weighs 150,000 pounds. It only takes six pounds per square inch of methane to lift it.
Methane is used to fuel the heat exchangers for the anaerobic digesters, keeping them at the 95 degrees needed. Still, about 50 percent of the methane is burned off.