The city of Superior is investing to upgrade the main wastewater treatment plant to improve the quality of effluent and improve the reliability of the plant.

Last week, the council approved more than $3.4 million in bids and up to $266,840 for engineering services for its secondary treatment and power distribution improvement projects.

The first component of the project will change the way the activated sludge treatment works. Instead of continuously stirring the tanks, the tanks will have a plug- or serpentine-flow, said Steve Roberts, Environmental Services Division administrator.

"That should help us with effluent quality," Roberts said. "We should have better control of settling and have lower solids content for a higher flow rate. It should also allow us more flexibility to grow the types of organisms that consume ammonia so we should have better effluent quality for ammonia without sacrificing phosphorous and solids."

As part of that project, Roberts said less efficient blowers that provide oxygen for the organisms in the basins will be replaced.

"What that's supposed to do is it's more of a modern design as they exist right now, so it's modernizing the tanks without building the new tanks," Roberts said.

The second component of the project would address the electrical system that keeps the plant operating. Four existing transformers will be replaced.

"Perhaps one of the more impactful changes is we're also working with Superior Water, Light and Power," Roberts said. "We will have two independent feeds from different substations. The plant will have better reliability so in case of a power outage, we could automatically switch over to the other substation."

By being able to keep the facility operating, Roberts said it reduces the risk of sanitary sewer overflows or sewer backups into basements.

"That's particularly important if we had a power outage during a storm," Roberts said.

The city in the process of signing contracts, and Roberts said he expects to know more about the construction schedule next month, but he expects some components of the project will be completed this year with the project as a whole getting done next year.

The project will be paid for with the state's Clean Water Fund Program loan.

"There's a couple of good things there," Roberts said. He said it's a subsidized loan that has principal forgiveness and there are loan dollars the city doesn't have to repay.

"That's going to be $750,000 on this particular project," Roberts said, adding that's the maximum amount allowed. "There are no rate increases associated with this project."