Ah, the Garden Giant. He’s a jolly fellow who roams around your garden at night tossing mulch as he merrily skips along, helping your veggies grow lush and tall.
Not quite. The Garden Giant is actually a species of mushroom, scientifically known as Stropharia rugosoannulata, that may hold a key to filtering harmful pollutants from stormwater runoff.
Although this mushroom can be rather “giant” as the name implies, growing up to eight inches tall and a foot wide at its cap, it is not the mushroom itself that does the work. It is something hidden underground — a fungal root-like material called mycelium. Mycelium is a microscopic, cobwebby, fungal thread that, when mixed with woody debris, decomposes bacteria.
Respected mycologist Paul Stamets and his team at Fungi Perfecti Research Lab have taken this natural strainer and developed a relatively simple biotechnology called mycofiltration that uses mushroom mycelium to filter stormwater runoff.
The technology was born 30 years ago when Stamets purchased the farm that is now the headquarters of his company and research lab. Soon after moving in he learned that, due to the few animals and a faulty septic system, his farm was discharging fecal coliform at levels that went far beyond the legal limit. The effluent was polluting shellfish beds downstream in Skookum Inlet in southern Puget Sound. Stamets was served with a court order and given a year to fix the problem.
Not one to take the traditional route to problem solving, Stamets decided to try using what he knew best … mushrooms.
“I knew from experience that the Garden Giant mycelium grows rather anemically in labs compared to other strains,” Stamets says. “But when it makes soil contact, the mycelium magically transforms into an extremely aggressive ropey white network that permeates into the ground and reaches far and wide.”
Stamets created a 200-foot bioswale at the edge of his farm, above the long drop down to the saltwater inlet. He filled the bioswale with a mix of Garden Giant mycelium and wood chips, and waited to see what would happen.
A year later water quality inspectors were shocked when they returned to find that despite the number of animals on the farm having doubled, there was more than a 99 percent reduction in fecal coliform content.
But it wasn’t until recently that Stamets was able to put this biotechnology through more rigorous lab testing. With the help of a grant from the Environmental Protection Agency, Fungi Perfecti partnered with the Civil and Environmental Engineering Department at Washington State University in 2012 to test the technology’s viability as a realistic urban stormwater management practice.
The research sought to determine which mushroom is most effective at filtering bacteria in urban environments. After testing a variety of species under various conditions, the research reaffirmed Stamets’ 1984 findings: The Garden Giant is the most efficient species for removing E. coli bacteria.
Furthermore, supporting research by Stamets and other mycologists indicates that this technique will likely reduce other harmful pollutants commonly found in urban stormwater runoff, such as heavy metals and polycyclic aromatic hydrocarbons, or PAHs. Mycelium can convert PAHs into fungal carbohydrates and may help absorb heavy metals.
Not only is this method efficient, but it has the potential to be a sustainable and cheap option for households, businesses and cities, says Alex Taylor, assistant researcher at Fungi Perfecti.
“Current methods of purifying water such as ozone and chlorine require large capital and structural investments,” Taylor says. “Our technology is very inexpensive and low-impact.”
The next step is to take this technology beyond the lab. The Fungi Perfecti team is now looking to partner with small businesses, municipalities and rain garden installers to conduct controlled field tests with urban mycofiltration.
“Right now we see mycofiltration as a treatment added to enhance the activity of existing stormwater management practices such as rain gardens,” Taylor says. “We can work together as a region to pioneer this technology.”
While rain gardens can capture pollutants, Taylor explained, they don’t effectively break them down. But by adding Garden Giant mycelium to the mix, the harmful substances can be transformed into carbohydrates and nutrients — which are actually useful to surrounding soil and plants.
So it seems that the Garden Giant may live up to its guardian of the garden reputation after all.