Each day, about 20 million gallons of sewage flows into the city of Tacoma’s wastewater treatment plants.
The water is separated, treated, and discharged into the Puget Sound, which leaves behind sludge—a mix of human excrement, industrial waste, and everything else that ends up in Tacoma’s sewers. The plants further treat the product to reduce pathogens, bacteria, heavy metals, and odors, and convert it into a fertilizer called biosolids, which is high in phosphorus, nitrogen, and other nutrients that help plants grow.
Tacoma produces about 5,000 dry tons of biosolids annually and sells it in bags under the brand name TAGRO to about 9,000 customers at local hardware stores, as well as to urban gardeners and farmers in the Tacoma region.
“The focus here has been on recycling and the production of beneficial products—clean water, energy, and soil amendment fertilizer … including biosolids,” said Dan Thompson, division manager of business operations for TAGRO.
Over 50 percent of the approximately 130 million wet tons of sludge produced nationally each year is treated and applied to cropland, which the U.S. Environmental Protection Agency (EPA) notes is less than 1 percent of U.S. farmland. As a fertilizer, it’s popular with some farmers because most wastewater treatment plants give it away for free or sell it at prices that are below than the cost of synthetic fertilizers.
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