There shouldn’t be a sweet smell of success associated with Oak Harbor’s whiz-bang new sewage treatment plant.

If fact, success shouldn’t have any odor at all.

Oak Harbor City Council approved a $4.5-million contract with Hoffman Construction Tuesday for an odor control system that’s supposed to eliminate all smells from the high-tech sewage treatment plant, now under construction in Windjammer Park.

“It’s part of a promise to the public that there wasn’t going to be odor coming from the facility,” project engineer Brett Arvidson said in an interview.

“The old one had pretty serious odor levels, as I’ve heard.”

When the project was being planned, some residents turned up their noses at the idea of building a new, smell-emitting campus of structures partially inside the waterfront park. Many didn’t want to repeat the mistake of building a sewage treatment plant in the park; the old facility, which will be completely torn down, was known to make a day at the park an eye-watering experience when the wind was blowing the wrong way.

In response, council members promised early on in the process that the new facility won’t make a big stink in the popular park.

Councilman Rick Alm-berg, who’s been closely involved with the project, said council members toured several facilities in the region when preparing plans for the treatment plant. He said odor control measures were an essential part of the modern plants and seemed to work perfectly.

He never smelled a rat or anything else.

While $4.5 million is nothing to be sniffed at, engineers went above and beyond to ensure that Oak Harbor’s plant passes the smell test, Arvidson said. He explained that biological odor eliminators are standard in such plants, but Oak Harbor also added activated carbon filtration to ensure scentlessness.

Much of the cost of the odor control contraptions, he said, comes from the complex of fans that will carry odoriferous air from the headworks and the dryer through the odor-eliminated structures, which will be built on the northern edge of the project.

The ventilation will move the “odor stream,” Arvidson explained, through the two-step process. First, the stink travels through a couple of different types of the biological processes in which bacteria living in special pellets and a sawdust-type medium absorb the smells.

“Let’s face it, most of these odors are organic,” he said.

After that, the cleaner air will go through the activated carbon filtering. Fans will push the de-smellified air upward so that any remaining stink — and there should be none — will go to high heaven.

With the contract for the odor control system, the total cost of the sewage treatment facility is currently at $102.4 million, not including sales tax or the cost of returning Windjammer Park to its pre-construction state, according to the presentation to city council.

City Administrator Doug Merriman said the city will determine the final cost of the project later this year. Once that’s complete, officials can determine how much sewer rates will have to increase in the future to pay for the project.

A city drawing shows what the sewage treatment plant will look like once complete.