After visiting with DC Water’s Bloom Biosolids team on Sustainability In Your Ear, we invited Chris Peot, Director of Resource Recovery at Bloom, to explain the beenfits of producing safe biosolids for agricultural use. 

Declining farm yields, soils stripped of nutrients, rising energy and fertilizer costs, dwindling carbon stores in soils, increasing droughts. What if part of the solution to these problems were just a flush away?

Biosolids are a nutrient-rich residual of wastewater treatment, a process designed to keep carbon and nutrients from upsetting the delicate balance in America’s waterways.  However, carbon is energy and nutrients are fertilizer; recovery of these resources can reduce utilities’ environmental and economic costs. With sustainable solutions for waste management and agricultural productivity needed now more than ever, biosolids offer a myriad of environmental and economic benefits.

What Are Biosolids?

Biosolids are a byproduct of the wastewater treatment process. After wastewater is treated to remove contaminants, the remaining solids are further processed to reduce or eliminate pathogens and odors, transforming them into a fertilizer rich in carbon and micro- and macro-nutrients. Depending on the level of treatment, biosolids are classified by the Environmental Protection Agency as either Class A Exceptional Quality, Class A, or Class B. Class A Exceptional Quality biosolids such as DC Water’s Bloom product meet strict standards for pathogen reduction and can be used to grow everything from food to flowers.

The recycling of wastewater to improve soil fertility is nothing new. As Lena Zeldovich writes about in her book The Other Dark Matter, sophisticated markets for “night soil” date back to imperial Japan and other parts of the world. Milorganite, Milwaukee’s bagged biosolids product, has been on the market for over a century. The product is such a favorite for lawn lovers it often sells out in the garden stores across the country.

Bloom, DC Water’s bulk soil amendment, has also developed a local following, selling an average of 60,000 tons per year since 2022. The Class A EQ designation allows the public to purchase Bloom directly from DC Water or from landscape supply stores and garden centers.  Research conducted at Virginia Tech and the University of Maryland in conjunction with partners such as the Maryland State Highway Authority has demonstrated Bloom’s use on soils and efficacy in establishing turf, crops and more in a variety of settings, from roadside soil conditions to newly established wetlands.

Enhancing Soil Health and Fertility

One of biosolids’ superpowers is the ability to improve soil health. Rich in essential nutrients such as nitrogen, biosolids act as a natural fertilizer that replenishes depleted soils. Unlike synthetic fertilizers, biosolids release nutrients slowly, providing a steady supply over time, reducing the risk of nutrient runoff. The organic matter (carbon) in biosolids also has myriad benefits – improving nutrient- and water-holding capacity in soils, increasing drought resistance, supplying food for beneficial microbes, decreasing erosion and much more.

By using biosolids, farmers and other growers can reduce their reliance on expensive, non-renewable fertilizers, while closing the nutrient loop, recycling natural materials back into the soil instead of disposing of them in landfills or incinerators.

Addressing Concerns about Contaminants

Understandably, there are some public concerns about potential contaminants in biosolids, the most nascent of them being PFAS. This ubiquitous group of 3,000+ manmade chemicals are fire, oil, grease, water and stain resistant, and are found in a wide array of consumer and industrial products, including non-stick cookware, paper, stain repellent, dental floss, cleaning products, food packaging, and cosmetics.

PFAS are ubiquitous in our society, and as a result, small concentrations end up in our sewers and biosolids products.  In communities with industries related to PFAS use, the wastewater residuals can have much higher concentrations.  Our Metro DC area has no such industries, so the PFAS levels in Bloom are no higher than background levels found in the rainwater itself, and much less than in the dust in our own homes and in the everyday products we use. We share concern over the presence of these chemicals in our society, and strongly believe that national efforts must focus on source control, or removal from the products we buy, as the sustainable solution.

Reducing Waste and Environmental Impact

The adoption of biosolids as a resource significantly reduces the volume of organic waste sent to landfills and incinerators. Wastewater treatment plants generate millions of tons of biosolids annually, and diverting this material from traditional disposal methods helps conserve valuable landfill space. Additionally, landfilling organic materials can produce methane, a potent greenhouse gas. At DC Water, a process called anaerobic digestion captures methane emitted in the process, generating 8 megawatts of power, approximately one third of the energy needed to operate our facility and making our plant the largest green energy project in the nation’s capital. DC Water’s carbon footprint was also slashed by 40% after putting in place thermal hydrolysis, which acts as a giant pressure cooker to kill all pathogens while also cutting the sheer volume of wastewater soils in half, reducing the need for energy-intensive trucking.

DC Water’s system upgrades not only resulted in a higher quality biosolids product, decreased carbon footprint, and a step toward a net-zero future, it also shrunk the utility’s costs, helping to abate future water bill increases and preserve resources to upgrade aging infrastructure and other priorities. Many wastewater treatment facilities generate energy through anaerobic digestion of biosolids, producing biogas that can be used for electricity or heating. This process reduces reliance on fossil fuels and supports the transition to renewable energy.

Biosolids are a remarkable example of how waste can be reclaimed for the valuable resources they contain, helping drive a more sustainable, circular economy in the process.

Editor’s Note: In January 2025, the U.S. Environmental Protection Agency (EPA) released a draft risk assessment evaluating the potential human health risks associated with per- and polyfluoroalkyl substances (PFAS), specifically perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), in biosolids.