If you contribute your daily bodily wastes to a municipal waste treatment plant, you are more than likely directly benefiting Washington soils.

According to Puyallup soil scientist Craig Cogger, each person in Washington produces about 60 pounds of biosolids per year. “Biosolid” is a euphemism for human waste and other inputs once they have been treated at a wastewater treatment plant. For the past 15 years, Cogger has helped spread biosolids on wheat land in Douglas County and studied the effect.

That effect has surprised him.

“We have seen a remarkable increase in organic matter,” he says, “despite the fact that the amount of biosolids is very modest.

Photo by Zach Mazur
Soil scientists Craig Cogger (left) and Doug Collins with rich organic no-till soil
(Photo Zach Mazur)

“We didn’t expect any long-term increase,” he says, referring to the difficulty of increasing organic matter in arid soils. “It seems to be a combination of biosolids and increased biomass” as a result.

Applying biosolids to agricultural land is permitted under the Clean Water Act. The use of Class B biosolids as a soil amendment is more tightly regulated than animal manure, says Cogger. “With manure, you have guidelines. With biosolids, it’s regulations.”

Class B biosolids are the basic refinement of wastewater treatment. They are stabilized and digested, resulting in some destruction of pathogens, similar to manure. Class A is heat-treated, through composting or drying, to kill pathogens. They are as clean or cleaner than native soil.

Biosolids are very rich in nitrogen and phosphorus, with smaller amounts of potassium and “pretty good levels of micronutrients.”

“Farmers in Douglas County really like it,” says Cogger, “because of the economic benefits, they get the equivalent or better yields [compared to synthetic fertilizers], and they see their soil getting better.”

However, in spite of 8 million people producing biosolids, they provide only a fraction of needed fertilizer.

Read more about Washington state soils in “A Fine Thin Skin

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