New Wenatchee Wastewater Treatment Plant Digestor Will Reduce Energy Spending

In early December, the City of Wenatchee announced an energy-saving revitalization project for their Wenatchee Wastewater Treatment Plant, including a new 4th digestor to help save thousands of kilowatts per year.

Although the project is independent to the increasing rate structure, the new digestor will be paid for partly from the 6% rate increase per year. City of Wenatchee Senior Utilities Engineer Jeremy Hoover explains the payment process for the new digestor.

"It's not like you turn on your faucet and you get an additional bill because you're using more water. It's not the same thing. For residential households, you get charged a base fee every month and that fee will be what's going up by 6% per year for the next several years."

This project will contribute to Chelan PUD's Strategic Energy Management project for 2021, which helped the city overall save about 201,363 kilowatt hours (kWh) a year, roughly $5,436.80 a year. Chelan PUD's media liaison Rachel Hansen explains how these energy savings helps in allowing the PUD to sell the surplus energy to wholesale power markets, keeping energy rates low for Chelan County customers.

Most of the machines within the wastewater treatment plant date back to the plant's opening in the 50's. Hoover states that his team compared different types of processors like centrifuges to rotational screen thickeners and found that the difference in energy use between the two types of technology was about 265,000 kilowatts per year.

Hoover explained that the improvements "will increase our capacity. It will not increase the amount of material that we're putting out. It will allow us to be expandable for the future, but part of the biggest driving factor on this project is redundancy." Hoover went on to say "We are planning on doing upgrades that will be saving energy at the plant. We will not be consuming as much energy for the various items because we're putting in newer technology."

The new digestor will help process and digest biosolids and release biosolid gas while thickening the material before it gets treated. The big energy savers were the thickeners and mixing components of the new digestor.

"Think of it like a big cake mix. If you don't have all your flour mixed up with all of your eggs, you get chunks of flour over here and some eggs over there and it doesn't work." Hoover then added, "think of it like a big plunger that goes up and down. That turned out to be a savings of approximately 119,000 kilowatts a year (at the waste treatment plant)."