And tree waste isn’t the only unwanted product that can be used to make this compost. Cities could also feed their trees with a little help from their human inhabitants: by recycling their poo.
A growing number of wastewater treatment plants are devising ways to produce safe soil amendments from recycled biosolids – the feces and other organic matter that passes through water treatment plants and often ends up in landfills or incinerators. DC Water, which provides water and sewer services to the US capital, is one example, creating a heat and pressure treated biosolid product called Bloom. It plans to sell about 60,000 tons to farmers, landscapers and other customers in 2022 alone. The goal is to change mindsets about human waste, says Chris Peot, director of resource recovery at DC Water. “It’s not a liability; its an asset.
Some cities are already using products from trees and human waste to enhance their urban greenery. In Austin, Texas, treated biosolids are composted with city tree and yard waste, then dried for several months to create a soil product called Dillo Dirt. It’s a product the city has been making for decades, and among its many applications, it’s used to aid in the planting and maintenance of trees. Since 2006, the city has managed to increase its tree cover 20 percent.
Meanwhile, in Washington, D.C., Bloom has been used to create a variety of blended products to improve the condition of soils, including a blend with sand, a blend that looks like potting soil, and a “woody blend” that includes pieces of aged hardwood. . If applied directly to soils, Bloom’s high nitrogen and phosphorus content would kill plants, says Peot, but mixing it with tree clippings, hardwood or other organic waste helps balance the nutrients. “We try to imitate natural soils,” he says.
April Thompson, Bloom’s director of marketing and sales, says gardeners have reported great results with the soil product on the grounds of the United States Capitol and in community gardens, among other applications. “Hemp, hops, hay. You name it, we probably helped develop it,” she says. This list includes street trees. As part of a contract with the city, a non-profit association Casey Trees used Bloom as part of his gardening toolkit around the capital. Over the next 10 years, DC aims to reverse the trend of urban tree loss and increase its canopy cover from 38% to 40%. Recent search suggests that the cooling effect this will provide could be lifesaving, especially given the ability of trees to temper the rapidly increasing urban surface temperatures.
Of course, recycling trees and human waste alone will not be enough to increase the number of trees in cities. But to help halt the decline of urban tree cover, it can be a very useful part of the solution, and hopefully spreads. DC Water consulted with plant operators in Virginia, Kentucky, Texas, California and elsewhere who are installing similar heat and pressure systems to turn their biosolids into plant-nutrient products.
“Entrepreneurs are all going up to them and saying, ‘Hey, we’re going to take this product away from you because it’s a problem,’” says Peot. “And we say, ‘No, it’s not a problem.'”