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How it's Made

How does the City of Tacoma make TAGRO products?

Made from what we call biosolids, which are highly treated—or pasteurized—wastewater byproducts as well as combinations of sand, sawdust, bark and other ingredients, TAGRO allows you to reuse our community’s resources to the benefit of your lawn and garden. And, because of improvements to the process that Tacoma uses to create its biosolids, the material that goes into TAGRO Potting Soil is virtually odor-free.

Here’s a little about how the wastewater treatment process works, and how we reuse biosolids to make TAGRO products:

The wastewater treatment process
Water that goes down our sink and toilet drains every day in our homes and businesses becomes wastewater. The City of Tacoma treats wastewater to separate and process the liquids and solids, then we return them to the environment. Because wastewater treatment destroys disease-causing organisms that may be in the wastewater, it protects public health and safeguards water quality, preventing pollution in our lakes, rivers and oceans.

Pretreatment
With the passage of the Clean Water Act of 1972, municipalities instituted programs to control the quality of wastewater discharged to the wastewater treatment system. Called pretreatment or source control programs, they have significantly improved the quality of our recycled water and biosolids. Businesses now recycle or use fewer hazardous products as a result of pretreatment programs.

Before business and industry can send wastewater through the public sewer system, they have to “pretreat” it to clean contaminants.

Grit Chamber
Once wastewater comes to a treatment facility, machines remove “grit” materials such as sticks, rags and pebbles.

The wastewater then slowly flows through large sedimentation tanks, where gravity physically separates solids from liquids. In secondary treatment the liquids go through aeration where the biological action of beneficial microorganisms removes additional organic matter.

From here, the final process disinfects the cleaned water, which is now ready to return to Commencement Bay.

Solids Treatment
The City of Tacoma uses what’s called Class A biosolids—EPA’s highest rating—so that our products are completely pathogen free. This way, we make sure that our biosolids are safe, and what’s more, they help us produce a product that consumers use in their very own yards.

In our dual digestion process, we actually cook our biosolids to kill pathogens and make our product safe to use in your home garden. Beneficial microorganisms decompose—or digest—the solids. This biological stabilization process destroys the potentially harmful pathogens contained in the solids—and reduces odors.

These stabilized solids are now called biosolids and are mostly organic matter, rich in essential plant nutrients. We can return biosolids in liquid or de-watered form to the environment as a soil conditioner, recycling them directly onto soils in the forest, on agricultural land or use them in landscaping and gardening.

We use a three temperature phase process during the anaerobic phase of our dual digestion to kill odors. At the three temperature levels, different populations of organisms do their jobs then die off, and a different population that doesn’t generate the same smelly gases takes over. It’s almost like ecological succession in a 21-day period.

Getting rid of the odor means the City of Tacoma can make more products that more consumers will enjoy using in their yards—and even indoor container gardens.

Read more about the solids treatment process and odor control in the article, Biosolids That Don't Stink (Honest!).

E-mail contact for this page: TAGRO