Residents of southwest Kalispell may breathe a little easier after the city’s wastewater treatment plant upgraded its in-ground air filters.

“We’re starting to have lots of neighbors, and we want to be a good neighbor,” said Curt Konecky, the plant manager. “So we decided during the last expansion process that we’d like to put an odor control bed in.”

The biologic odor-control filter beds were first installed during a $22 million expansion that began in 2007. The goal was to mitigate odors that come with the job of wastewater treatment.

The plant filled two large, square blocks with wood chips and bark. Then air from the most foul parts of the plant was piped to the bottom of the beds, where it would be filtered.

The wood chips and bark, which Konecky calls “media,” lasted six years. When it came time to refill the beds, Konecky said other plants had moved away from wood chips because they tend to settle and compact.

“We decided to use large western fir bark,” Konecky said of the new material. “What the media does is creates a surface area, a moist surface area, for microorganisms to grow that actually eat the odor.”

Water is sprayed in the middle of the beds and on top to foster an environment for the mircroorganisms to grow. Konecky said the mircroorganisms don’t have to be introduced. They build their own cultures to battle the serious odor offenders — hydrosulfide and methane.

The city trucked in 1,400 cubic yards of bark to refill the filters. The two beds are each about four feet deep.

It cost $38,880, or about $27 per cubic yard, to replace the media.

That project was completed May 18 and is up and running. The plant hopes to get at least six years out of the media.

After conducting a study, the plant chose the smelliest air in the facility to be filtered. It’s pumped in by fan from the Evergreen discharge, truck storage, fermenter tank and dewatering areas, Konecky said.

For most of the plant’s 60-plus-year history, there were few neighborhoods around the treatment plant. Kalispell’s population has increased over the years and now vast neighborhoods lie just across Airport Road.

Prior to the 2007 expansion, the plant had no odor mitigation system.

With the new media in place, Konecky said that a typical visitor could stand next to the beds and get a mild “earthy” scent.

Reporter Matt Hudson may be reached at 758-4459 or by email at mhudson@dailyinterlake.com.