Regional Policy Gets Odors Under Control in Northwest

King County, Wash., sets odor control ordinance regulating 34 local wastewater systems

King County, Wash., takes pride in being a good neighbor. For over a year, county officials have worked closely with local municipalities to reduce odors. And they continue to conduct extensive research and pilot studies to develop cost-effective, cutting-edge odor control technology.
In July 2003, the Metropolitan King County Council approved an ordinance designed to mitigate the odors that may be emitted from wastewater treatment facilities within the county. The ordinance paved the way for more than $5 million in capital improvements, spanning three years, to reduce and prevent off-site odors from King County’s two regional wastewater treatment plants. The policy was recommended after nearly 18 months of study.
King County safeguards the environment and public health by treating 200 mgd of wastewater. The county’s system monitors for odors continuously at various points in its large system of treatment plants, pipe networks and pump stations.
Thirty-four local sewer districts within King County’s wastewater service area own and operate local collection
systems and send their wastewater to the county’s wider-diameter pipelines.

Taking action against odors

Whenever wastewater odor is detected, workers promptly take action in several ways:

  • Adding chemicals or biological enzymes at strategic points in the pipeline system;
  • Installing odor scrubbers using wet chemicals or activated carbon in high-odor spots;
  • Chlorinating the wastewater coming into the treatment plant; and
  • Replying promptly to residents’ complaints, assuring them of the steps being taken to resolve the problem.

Odor control methods used

King County, as well as the local municipalities within the county, use the following odor control devices:
Chemical Scrubber—Foul air is forced through a “rain” of a chemical and water solution, which absorbs the odors.
Activated Carbon Scrubber—Foul air is forced through a bed of activated carbon granules. The granules absorb
the odor.
Biological Treatment—Foul air is passed through a biologically active filter (or scrubber) where bacteria digest contaminants and neutralize odors.
Chemical Addition to the Wastewater Flow—Chemicals are added directly to the flow of wastewater, usually through a manhole at locations where odors have been troublesome. The chemicals reduce bacterial growth and neutralize odors.
Contained Facilities—Some processes at the treatment facilities are enclosed in buildings, and the air is scrubbed before being released into the environment.
“We believe the program will provide the best odor prevention possible for facilities that have been protecting public health and water quality for nearly 40 years…We want to retrofit the plants to a level that reflects best in the country for existing facilities,” King County executive Ron Sims stated.
Eighteen cities (including Seattle), 15 water and sewer districts, and the Muckleshoot Indian Tribe comprise King County’s wastewater treatment services area.
A wholesale service provider, King County bills the local agencies based on the number of “residential customer equivalents” in their districts, and these local agencies in turn bill their customers.


About the author