What are biosolids? Is Loop the same thing?

Biosolids are the fertilizing and soil building products created by wastewater facilities around the world. Wastewater facilities can do more than just clean the water, they can also turn the valuable resources in the water into useful products like biosolids, biogas (renewable energy) and recycled water. This is what King County does. King County’s biosolids are called Loop®, and Loop is rich in essential nutrients and organic matter that plants love.

How is Loop made?

All the water that comes to the plant from homes and business is first separated into “solid” and “liquid” streams using gravity. Then, the “liquid” (the water) goes to its own part of the plant to be cleaned and to be turned into recycled water for things like irrigation and street cleaning. The “solids” (essentially the poop and the food) are put into a big heated tank called an anaerobic digester. In the digester, beneficial microorganisms, the same ones that live in our own digestive system, break down the material until it is biologically transformed, all while creating biogas (renewable energy). When this process is complete, extra water is removed, leaving a fertilizer and soil builder that is full of the essential nutrients and organic matter.

Are biosolids the same as "sewage sludge" or “raw sewage”?

No. No more than bread dough is the same as a loaf of bread. Biosolids are the end-result of regulated treatment processes, such as anaerobic digestion at warm temperatures. The solids extracted from wastewater only become biosolids after treatment.

What does Loop look like?

Loop looks like black mud. It’s somewhat crumbly but also sort of spongy, much like Play-Doh. Sometimes Loop sparkles with struvite, a beneficial phosphorus and nitrogen-rich mineral.

What does Loop smell like?

Freshly applied Loop can have an odor, usually described as “earthy” or “organic,” similar in some respects to bone meal or manure; people often describe a hint of “ammonia” to the odor as well. After being worked into the soil the odor typically goes away within a short time.

Compost or soil mixes that contain biosolids, like GroCo compost made with Loop, have much less odor — usually quite similar to potting soil or any other organic mulch. People often describe GroCo compost as having an earthy aroma, similar to a forest floor.

Where can I get Loop?

Loop is available in the Puget Sound area as an ingredient in the commercial compost product GroCo. Visit the Gardens & Landscapes page to see how GroCo is used and where it is sold.

Commercial growers in Douglas or Yakima counties can contact Boulder Park Inc. or Natural Selection Farms respectively. Visit the Our Partners page  for more information on these customers, or see why they love Loop on the Testimonials page.

What is GroCo and how is it produced?

GroCo compost is a natural, soil building compost. GroCo is produced by composting 3 parts sawdust with 1 part Loop. Visit the Garden & Landscape page for more information.

What is the nutrient value of GroCo?

The nutrients found in Loop are also found in GroCo compost. It contains both macro- and micronutrients beneficial for plant growth. On a dry weight basis GroCo typically contains 1.24% N (total nitrogen), 2.04% P (as P2O5), and 0.2% K (as K2O). Visit the Loop is Awesome page for more information.

How do I use GroCo compost?

Add it to annual flower and vegetable beds, turf, perennial shrubs and trees, even indoor plants! Visit the Gardens & Landscapes page for more information.

What else could King County do with Loop?

New innovative technologies are continually reviewed and pilot tested by our technology assessment team and university researchers, because we want to be the leader in our field. But it turns out, what we’ve been doing for decades is still pretty innovative and cost effective for our ratepayers. Not only do we harness renewable energy to power our treatment plants, but using Loop on farms, forests and gardens recycles nutrients, makes plants thrive, and helps us grow food for sustainable communities. Loop even helps us fight climate change.

Because the benefits and safety of using biosolids has been demonstrated for decades, Washington State Department of Ecology mandates that biosolids are used as a soil builder and fertilizer, conserving landfill space for waste materials. If we tried to burn Loop, it would create air pollution and would take a lot of energy because Loop is mostly water.

If we didn’t use Loop on farms, forests and gardens, we would waste all these benefits. Check out how different uses of Loop stack up in the diagram below.

How do uses of Loop stack up2

What are the long-term effects of land application of Loop?

Loop has been used as a fertilizer and soil builder for decades, with a long list of happy customers. The long-term effects of Loop are healthy, fertile soil. Loop improves soil fertility and supports healthy plants. Long-term (20+ years), peer reviewed, academic studies show significant increases in soil organic matter and improved soil structure, both measures of healthy soil.

Is biosolids recycling safe?

Yes, Loop is very similar to any other natural fertilizer or soil builder, such as manure. Visit the Science page for more information.

What can I do to protect the quality of Loop?

The best way to protect the quality of Loop is to prevent putting certain waste down the drain. The following items should go in the trash, not in the toilet or the sink:

  • Stickers from fruits or vegetables
  • Plastic and other non-organic materials like condoms or tampons
  • Expired/unwanted prescription or over-the-counter drugs.
  • Grease and other fat from the kitchen
  • Disposable wipes, diapers, and liners, even if they are labelled as “flushable”
  • Products labeled “danger”, “hazardous” or “toxic”

Try to use fewer cleaning products and chemicals at home and switch to “biodegradable” or more natural alternatives.

Remember: only toilet paper and human waste should get flushed.

Are there toxic substances in Loop?

Only because there are toxic substances everywhere. Visit the Science page for more information.

Are there disease-causing organisms (pathogens) in Loop?

Not for long! Visit the Science page for more information.

Does using Loop affect surface or ground water?

No. Visit the Science page for more information.

Where can I get more information about the King County Biosolids Program?

Visit the King County’s Biosolids Program page for more information.

What are some of the hot topics that people are discussing these days?

Some folks have raised concerns recently about Loop and other similar products. If you have questions or concerns about biosolids and would like to learn more, click here for more information about some of the most common questions related to Loop.