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Biosolids Dryer and Plant Odor

At a glance

  • What: The biosolids dryer at the wastewater plant (an ARPA-funded project begun in 2023) and the odor complaints near the plant.
  • Where it stands: The dryer is nearly complete but has been starting and stopping, and was off again after a drive chain broke. Staff are running a study of odor control for the dryer vents and an update to the odor study (about six months).
  • Next: Completion by the end of December for the ARPA deadline; a final cost update to Council about a month after October 20; odor study results; about 3.6 million dollars of further odor control planned for 2029 to 2031.

Details

  • The dryer uses solar heat and floor plates heated with digester biogas, removes close to 18 tons of water a day and cuts landfill hauls from daily to one or two a week. The county landfill raised its biosolids rate from 33 to 50 dollars a ton in October.
  • Complaints normally rise in September and October; the 2020 to 2021 study accepted odors above background on 3 to 5 percent of days at a 900 foot residential buffer, and complaints run at about 2 percent of days. Odor control on the centrifuge stack was completed in early 2026.
  • Council members asked about the risk if the dryer is not running continuously, and one suggested making the odor phone number easier to find online; staff agreed to work on the website.
  • Related: odor was also the main topic when Council approved WRRF Annexation and Rezone next to the plant; see also Timbercreek Recycling Transition.

Sources

Log

2026-10-20 - City Council Work Session

Update from Public Works on the dryer (ARPA deadline end of December, startup problems, landfill savings) and on odor complaints, studies and planned odor control. Council asked about risk and communication; no vote.