Unless you use a septic system, the water you send down the drain in the City of Carnation travels through pipes owned and maintained by the City of Carnation to King County’s Carnation Treatment Plant. At this plant, we process about 111,000 gallons of wastewater every day. After we treat the water, we release it to the wetlands of the Chinook Bend Natural Area. About 35 million gallons of clean, recycled wastewater are sent to the Chinook Bend Natural Area every year. This water flows to where approximately 20 percent of the region’s Chinook salmon return to the Snoqualmie River Watershed to spawn.

The Carnation Treatment Plant started operating in 2008. We estimate that the plant treats wastewater from about 2,000 people in Carnation’s downtown area. As local population grows, and more people connect to the sewer system, King County will continue to invest in and upgrade the plant.

Cold and rain brought new challenges for treatment plant staff this past winter

From the outside, the Carnation Treatment Plant looks like a large, industrial facility. Inside, it is filled with pipes, pumps, and tanks that work to treat wastewater. But the people operating that infrastructure are truly our greatest asset.

Each year, our operations and maintenance staff work hard to be well-prepared for the rainy season. This winter, our crews went above and beyond to keep treatment processes going at the plant, despite extremely cold temperatures and higher than normal wastewater volumes.

This winter was historically cold for our region. During one particularly cold stretch, some pipes, valves, and other critical treatment equipment froze. To keep the plant working as usual, staff used blow torches to warm up some of the pipes we use to keep wastewater flowing! Our operations, mechanical, and electrical staff work together to resolve issues like these. We are now upgrading vulnerable insulation, piping, and electrical cables to be ready for extreme cold in the future.

More flow means more trash and debris

The heavy rains of winter also brought higher than normal wastewater flows. The Carnation treatment plant experienced a 32 percent increase in incoming wastewater on several days in January. The plant is designed to handle higher than historically recorded flows in the winter, but the increase in flow this year overwhelmed the screens that are used to filter out trash and debris from incoming wastewater. Operations staff spent extra time caring for the filtration screens to make sure all wastewater flowed through the treatment plant.

In January, we completed several upgrades to overhaul the screens. This helped accommodate debris coming with the increased flows. Plant operators spent the night at the treatment plant to monitor wastewater flow and ensure debris was screened out overnight.

Keeping the bacteria that clean our wastewater happy

All King County treatment plants use processes that mimic how nature cleans water. Mechanical systems remove solids and floating material, and microorganisms (bacteria) help break down organic matter and remove nutrients. Like other living creatures, the bacteria we use to clean wastewater need the right combination of air and food to thrive. We use chemicals at key steps in the treatment process to help maintain favorable conditions for these bacteria to survive and treat the wastewater.

We recently tested using a familiar and safer chemical to treat wastewater at the Carnation Treatment Plant. This chemical is magnesium hydroxide, which is the main ingredient of milk of magnesia, improves treatment efficiency, saves ratepayer money, and minimizes the use of corrosive chemicals. Based on the success of the pilot test, we are working to install a permanent magnesium hydroxide system at the treatment plant in the coming years.

Membrane system upgrades will keep our system working

After bacteria clean the wastewater, the mixture of treated wastewater and bacteria enters our advanced membrane bioreactor system. This system uses fine filters that remove small particles while allowing water molecules and dissolved material such as salts to pass through. This year we will upgrade the membrane system. 

Learn more about wastewater treatment in your area!

Our goal as a community partner is to share information about our operations and maintenance activities and provide educational opportunities.

Are you interested in learning more about your local treatment plant? Check out our website where you can learn more about our each of our five treatment plants. You can also contact our Education team and schedule a tour at an available plant, or watch a virtual tour on our YouTube channel – also available in Español (Spanish) and for elementary aged children.