Most Twin Cities residents don't think twice about what they flush down the toilet, as long as it doesn't return. But processing human waste is a sophisticated, full-time job for one of the nation's largest treatment plants, in St. Paul.
The Metropolitan Wastewater Treatment Plant, owned and operated by the Metropolitan Council, is preparing for $137 million in improvements over several years. The upgrades, the second phase of projects identified more than 10 years ago, target everything from air systems to electrical distribution at the 77-year-old plant.
Such maintenance is common at the facility, but offers a window into the web of operations — from tiny microorganisms to massive incinerators — that purify the wastewater of a third of Minnesota's population. The process churns 24 hours a day on the sprawling campus tucked between the Mississippi River and Pigs Eye Lake, at the tail end of an industrial road.
It's the kind of place with buildings labeled "sludge processing," where staff members say things like "there's really a high BTU value in scum." But it also has a good reputation, winning perfect-compliance awards for three consecutive years from a national industry group that tracks plants adherence to state discharge permits.
"For a typical plant, there's hundreds of opportunities every year for something to not be quite what it's supposed to be," said Glen Daigger, a professor at the University of Michigan who has worked at the plant as a consultant. "For a plant to go years and years and be in full compliance, it's a pretty difficult thing."
That's important, since the final product ends up in the Mississippi River about 24 hours after it arrives.
"The [treated] water is cleaner than the river it's going into," said Mike Mereness, assistant general manager of operations at Metropolitan Council Environmental Services, which oversees all the plants.
The plant's 250 million gallon daily capacity makes it the 10th-largest in the country — the largest is in Chicago — and it normally handles about 170 million gallons a day. It is by far the largest of eight plants owned by the Met Council, serving more than 60 Minnesota cities.