Dane County Executive Joe Parisi says new equipment will help remove harmful phosphorus from lakes‘Game changer’ for cleanup
An unprecedented lakes cleanup effort is under way, but don’t expect the unmistakable summer stink to go away anytime soon.
Not for a decade, at least.
“As we start adding up these new policies and practices, the results will accumulate,” says Don Heilman, director of the Clean Lakes Alliance. “A lot of good work is being done, but we have a ways to go.”
Over the last three years, the Clean Lakes Alliance, Dane County, area farmers and the Madison Metropolitan Sewerage District have undertaken an aggressive effort to keep phosphorus from entering Lake Mendota — the northernmost link in Dane County’s chain of lakes.
Phosphorus, largely from cow manure, was a major contributor to the blue-green algae blooms that proliferated in 2008 and 2009, causing area beach closures.
Heilman says the goal is to reduce the annual phosphorus discharge across Dane County’s lakes by 46,000 pounds by 2025. It’s an attainable figure, according to Dick Lathrop, who has studied the area’s lakes since 1975.
“We can do it if we can get the financial backing,” he says.
A retired Department of Natural Resources research limnologist, Lathrop says the county has tried cutting the phosphorus loads for decades.
“Some progress was made,” he says, “but the problem is so large, and new problems keep cropping up.”
Lathrop says the intensified focus on manure management around the north Mendota watershed is as aggressive an effort as he has seen.
While farmers around Lake Mendota continue to adopt more progressive farming strategies, Dane County Executive Joe Parisi says a second manure digester is slated to go online this month.
The first digester, online since 2011, has kept 170,000 pounds of phosphorus out of the lakes, he adds.
The manure, which accounts for 75% of the lakes’ phosphorus load, is put through an anaerobic digestion process; liquids are separated from the solids.
Methane gas is captured and burned, churning electricity-producing generators.
“The digesters are critical to our lakes cleanup effort,” Parisi says. “And they generate clean energy, too, which is extremely important. Each one can generate enough clean energy to power 2,500 homes.”
Because the digesters remove only 60% of the phosphorus, Parisi says the county is purchasing a machine, called a nutrient concentration system, that will capture the remaining 40%.
“It’s a game changer,” he says.
Kristi Sorsa, a program manager with the city’s public health department, says the effort appears to be working, noting that beach closures over the last few years due to algae blooms have dipped from their pre-2010 levels.
While Lathrop praises the effort, he says there is always more that could be done.
“The manure going into the two digesters only accounts for about 15% of the manure within the watershed,” he says. “There is still a lot of raw manure being spread around.”