DC Water Markets its Biosolids as Bloom

DC Water is marketing its EPA-certified “Exceptional Quality” Class A Biosolids as a retail soil additive called Bloom. Biosolids are merely the sludge that comes out of a waste water treatment plant. DC Water is not the first wastewater utility or DC area utility to turn its wastewater biosolids into a soil additive for home gardeners and crops for human consumption. AlexRenew sells their Class A Exceptional Quality bio-solids to farmers in Virginia; and some of the Class A Biosolids are combined with wood fines, creating a soil amendment product that they are calling “George’s Old Town Blend.”

At Blue Plains and other sewer treatment plants primary treatment uses screens to remove large solids from wastewater which then sits in settling tanks, which are designed to hold the wastewater for several hours. During that time, most of the heavier solids fall to the bottom of the tank, where they become a thick slurry known as primary sludge.

The sludge is separated from the wastewater during the primary treatment is further screened and allowed to gravity thicken in a tank. Then the sludge is mixed with the solids collected from the secondary and denitrification units. The combined solids are pumped to tanks where they are heated to destroy pathogens and further reduce the volume of solids. With treatment sludge is transformed (at least in name) to Biosolids.

In 2015 DC Water unveiled the newly completed and operational sludge treatment system. Blue Plaines now has Cambi thermal hydrolysis trains, four digesters, dewatering equipment and a combined heat and power plant that cost $470 million. The new digestor system uses thermal hydrolysis (heating to over 160 degrees under high pressure) followed by anaerobic digestors.

The system produces methane gas which is captured and used to run turbines to produce power that supplies over one third of the electric power at Blue Plains (about $10 million in electric costs) and the digestion process destroys nearly one half of the Biosolids and producing Class A Biosolids reducing the chemical treatment costs and the transportation costs to get rid of the Biosolids.

Though this processing of Biosolids into Class A will save DC Water $13 million in chemical treatment and transportation costs a year, the project has a payback of over 20 years. This was not about savings, but rather better sewage treatment in an urban environment and better management of nutrients. Class A Biosolids are safer and easier to use in agriculture. Bloom, the name DC Water gave to the Class A Biosolids product, can increase organic content in the soil, increase drought resistance in plants, and provide essential plant nutrients such as nitrogen and phosphorus. DC Water intends to sell a substantial portion of the residual Biosolids product as a soil just as Milwaukee’s waste water treatment plant sells their Class A Biosolids called “Milorganite” in bags at garden centers.

To ensure that Biosolids applied to the land as fertilizer do not threaten public health, the EPA created the 40 CFR Part 503 Rule in 1989 that is still in effect today. It categorizes Biosolids as Class A or B, depending on the level of fecal coliform and salmonella bacteria in the material and restricts the use based on classification. The Biosolids are tested for fecal coliform and salmonella and composite sampling is done for heavy metals and hydrocarbons; the presence of other emerging contaminants in the Biosolids is not tracked.

The land application of Class B Biosolids has been a growing area of concern. Research at the University of Virginia found that organic chemicals persist in the Class B Biosolids and can be introduced into the food chain; however, Class A Biosolids have been found to be safe. According to Dr. Greg Evanylo, a Professor at Virginia Tech, there are well recognized processes to kill pathogens. In addition DC Water states that trace contaminants in Biosolids are not a threat to public health and the environment, and Bloom saves energy and reduces our carbon footprint when compared to conventional petroleum based fertilizers.

Currently, there are two types of Bloom: Fresh and Cured. Fresh is cheaper and contains more moisture. Because it contains more moisture, it is heavier and the price difference is partially paying for water weight. Cured has less moisture. Because it is dryer it is lighter.