The biosolids at the bottom of Kennewick's wastewater treatment lagoon aren't being wasted.
They are being transformed into fertilizer for a dryland wheat farm about 15 miles south of Kennewick.
"Waste is a resource out of place," said John Griffin, Kennewick's plant services supervisor.
That is something that is being fixed by Merrell Bros. of Kokomo, Ind. The company was hired to remove 6,000 dry tons of biosolids from the city's No. 1 lagoon so Natural Selection Farms of Sunnyside can apply them to farmland.
The $2.4 million project involves a process where water is separated from liquid biosolids that have the consistency of chocolate milk, leaving behind a compressed mass that looks like coffee grounds.
Whenever water runs down a drain in a home or business, a toilet is flushed or potatoes are washed, the resulting wastewater is sent to the city's treatment plant. Griffin said the city receives about 300,000 gallons of wastewater each day.
The biosolids from the city's wastewater treatment plant are the end result of aerobic digestion and include organic and inorganic materials, Griffin said. They have nitrogen, potassium, phosphorus and minerals beneficial to plants.
The biosolids recycling process is regulated by the state Department of Ecology, which gave the OK for the city to start after the biosolids met the required tests, Griffin said.
The lagoons have to be emptied every five to six years, Griffin said.
Dustin Smith, Merrell Bros. chief business development officer, said the process to dewater biosolids has existed for about 30 years, but Merrell Bros. started using it about 10 years ago. It's become more popular because of high transportation costs.
Less hauling is involved than if the biosolids still were in liquid form, Griffin said.
Removing 6,000 dry tons of biosolids means pumping about 48 million gallons of liquid biosolids, Smith said.
The biosolids are pumped from the lagoon by a dredge. Attached to the boat is a rototiller-type head that cuts up the solids and vacuums the liquid up and into a pipe, Smith said.
The biosolids flow through a hose and enter a mixing tank, he said. A white liquid called polymer is added, which causes the solids to bind together, allowing clear water to fall through the pervious conveyer belts between which the biosolids are squeezed as they pass around rollers.
Merrell Bros. has nine of the belt filter presses running at once, with the end of each belt pouring the dark-looking fertilizer into a waiting semi.
One full revolution takes between one and two minutes, Smith said. The water is pumped back into the city's lagoon.
Clear water fills most of the lagoon, where the company already has pumped. About three more weeks of work remain, he said.
Since the eight-person Merrell Bros. crew started Aug. 1, Smith said it has removed about 5,200 dry tons of biosolids. If more than 6,000 dry tons are in the lagoon, which is likely, Griffin said there is a portion of the contract that allows the city to have more removed in increments of 500 tons for more money.
The sewer utility rates Kennewick residents pay funded this project.
Putting the biosolids into a landfill would cost about half of the contract with Merrell Bros., Griffin said.
About 900 to 1,000 truckloads are being taken from the city's wastewater treatment plant to a Benton County farm, Smith said.
At the farm, a truck with a side slinger sprays the biosolids evenly on the field, said Brian Campbell, biosolids coordinator for Natural Selection Farms. The trucks have flotation tires, so they compact the ground less than regular tires would.
Before the biosolids can be applied, both they and the soil are tested for nutrient content so the correct amount can be applied, he said.
Adding the organic matter to the soil helps keep it together, said Ted Durfey, owner of Natural Selection Farms. It increases water retention and limits wind and water erosion.
The amount is calculated to what would work best for the crop, he said.
And the nitrogen from the biosolids doesn't leach into the soil as it does with commercial fertilizer. Plants use the nutrients as needed, so more than one year's crop can benefit, Durfey said.
The goal is to be able to cover all 1,400 acres of farmland available, he said. He has seven employees working on the project.
-- Kristi Pihl: 582-1512; email@example.com