The region’s wastewater agency is spending $19 million to reduce pollution from sludge burning and replace aging components at its treatment plant in Eagan.
The Metropolitan Council took initial action Tuesday to approve the upgrades to the Seneca wastewater plant, the second-largest plant in the metro area by capacity. The changes will help the plant meet air emissions standards issued under the Obama administration.
The Met Council collects and treats the Twin Cities’ wastewater through 600 miles of pipes and eight treatment plants scattered around the area. The plant primarily treats waste from the southern suburbs of Bloomington, Eagan, Burnsville and Savage, and discharges the purified water into the Minnesota River.
Like its larger cousin in St. Paul, the Metropolitan Wastewater Treatment Plant, Seneca incinerates the sludge left behind during the purification process. This produces emissions such as sulfur dioxide, though they amount to a small fraction of what comes out of the state’s power plants, according to data from the Minnesota Pollution Control Agency.
Other treatment plants in the region convert sludge into a fertilizer or ship it to the Metropolitan plant for incineration.
Seneca is one of about 40 wastewater plants in the country that needed improvements to comply with Environmental Protection Agency rules on sewage sludge incinerators, based on a 2016 fact sheet from the U.S. Environmental Protection Agency.
“We’ve demonstrated compliance with our requirements for sewage sludge incinerators,” said Rene Heflin, the council’s manager of plant engineering technical services. “We’re operating very well and able to meet our emissions limits.”
The plant installed a temporary exhaust system to comply with the standards last year, until the permanent changes are made. The overhaul includes new scrubbing technologies that remove pollutants.
Other improvements will make the plant more energy efficient, such as replacing spinning centrifuges with a gravity system to dry the sludge.
The remaining half of the project will rehab aging components in the plant, like replacing a multilevel roof and an odor control system. Seneca was constructed in 1972.
“We’re seeing that at all of our plants that the asset preservation is … becoming the primary component of our projects,” Heflin said.
It’s not the only council wastewater facility undergoing upgrades this year. The massive Metropolitan Plant, which is the 10th largest facility in the country, is in the midst of a $137 million multiyear overhaul.
The council is also spending about $100 million a year rehabbing its system of large sewers, known as interceptors.