Let’s Talk Biosolids!
Recently we have been learning about biosolids- how they are made and where they are used. After the heavy organic solids (mostly human and food waste) are strained from sewage, they are composted with bacteria for about a month to remove pathogens. About half of these biosolids are then trucked off to commercial forests and farms*. Their use is carefully monitored because of their pathogen content, which is too high for residential use. After application the area is typically closed for a period of time.
The remainder is combined with wood shavings, composted about three months and used as compost/fertilizer for home gardens. Biosolids are a great alternative to chemical fertilizers such as Urea and keep waste out of the landfill or incinerator. They are just as beneficial to plants as chemical fertilizers, but don¹t leech into the water system (a major concern with chemicals). At home, you can compost food scraps, which makes a great, free soil additive. It seemed like the biosolids would be gross, but the composted samples I saw looked just like normal nutritious soil.
Our class is conducting an experiment to compare plant growth in three different types of soil- one of which is biosolids! The Mountains to Sound Greenway Trust uses the commercial, less composted biosolids from King County Waste Treatment Plants on forests to speed growth. Our guest teacher, Nancy Lomneth, showed us a tree ring cross-section. The growth increase was phenomenal. It looked the growth more than doubled once the biosolids were added! Also, unlike with chemical fertilizers, the positive effects of biosolids last for years. The Greenway provides a vital link between wild lands, thus drastically increasing the potential range area for wildlife, as well as saving forests from harvest. Local residents can enjoy the Greenway through a variety of hiking trails or even volunteer to plant trees and restore Greenway ecosystems.
*(Editor¹s note: The vast majority of our biosolids get used on wheat farms, where farmers typically wait 4 years to receive biosolids to fertilize their fields. They are also used on other crops in eastern Washington like hops and corn. They are perfectly safe, and they produce yields far better than that with synthetic fertilizer — that’s why the farmers like them so much. These biosolids are composted for one year.)
Guest blogger Dylan W. is 17 years old, a junior at Roosevelt High School in Seattle and plans to attend college. Thanks Dylan!