Kirk Farris faced a dilemma after discovering cracks at the bottoms of his clean-water plant’s 23-year-old secondary clarifiers. 

Farris, lead wastewater operator and superintendent at the Nixa (Missouri) Wastewater Treatment Plant, had to juggle the cost-benefit of whether to rehabilitate, regrout or completely replace the two clarifiers.

“We could have just regrouted it, which we’ve done in the past,” says Farris. “But we needed a more holistic approach.” In the end, Farris opted to work with contractor Midwest Infrastructure Coatings to coat one of the 120-foot-diameter clarifiers with polyurea, supplied by OBIC.

Extending life

“The city had worked with Midwest and Michael Vavruska lining our manholes for quite a while,” says Farris. “They came highly recommended by our collections team. In summer 2024, the subcontractor Blast It Clean began sandblasting and pressure washing the clarifier to prepare for application of the polyurea coating.” Blast It Clean also painted the steel rotation assembly prior to the OBIC polyurea being applied to the concrete surfaces.

Vavruska observes, “Adhesion is everything. A lot of concrete preparation went into this. We pressure-washed the concrete not only to knock off old scaling but to cut grooves into it to help with adhesion.”

The Midwest team ultimately coated over 15,000 square feet of surface concrete in 15 days. The process took roughly six weeks. Since the clarifiers are uncovered, weather slightly affected the project timeline and also incited concerns about whether the plant had capacity to manage high flows while one clarifier was out of service.

“It was a big fear not being able to pull that clarifier into service if we needed it,” recalls Farris. “We did run into one or two rain events where, as opposed to being able to pull on that third clarifier, we had to bring an old oxidation ditch online. But we were able to make it through.”

Slip and slide

While Farris has few hard numbers to share about the project’s benefits, he did list plenty of results his team has seen since the coating project. “First off, having the clarifier coated versus completely rebuilding it was leaps and bounds different in cost,” he says. “It would have been a multimillion dollar project to tear out and redo the clarifier, as opposed to recoating it and regaining about 50 years of useful life.

“We probably now hose down the clarifier half as often as we did before. If you consider the hourly cost of labor, the savings add up quickly.”

Vavruska adds, “From my point of view, if we can save the operators hours of time in washing that tank out for what typically has taken days and give them the opportunity to tackle another task around the plant, that’s success.”

The rejuvenated clarifier has brought pride to the facility team. “You don’t really get to think about aesthetics in our industry,” Farris says. “It’s function over the way it looks. But to have something that doesn’t look like you’d find it in a wastewater plant, and that you can show on a tour for the city council or anyone else, that’s something to be proud of.  

“Also, from a compliance standpoint, an inspector could come and see the cracks at the bottom of the clarifier,” adds Farris. “We’re not going to get written up over it, but they’re going to put it in the report. By coating it and filling in those cracks, we’re in better standing with regulatory agencies.”

Ongoing partnership

While the clarifier project is complete, Midwest will continue working with the Nixa to coat manholes as the city strives to control inflow and infiltration in the collection system.

Vavruska says, “We’ve done manholes for the city for three years with Kirk’s collection system colleagues at the public works department. They’ve got more for us this year. I hope this business relationship we’ve made with Nixa is a long, ongoing one. They’re great to work for.

“I’ve come across several towns just like Nixa. They understand that this old infrastructure can’t just be dug up and replaced; it’s not cost-effective. So, whenever you find products that will extend the useful life for a fraction of the cost, it’s a win. I love seeing towns looking at that option, because they are truly doing the taxpayers a service.”

Nixa officials plan to repeat the coating project for the city’s other clarifiers in the next few years. They have a good idea who they’re going to call.