Wastewater is now providing a significant amount of clean electricity for a wastewater plant in Washington, D.C. The District of Columbia Water and Sewer Authority — better known as DC Water — has started using its new $470 million waste-to-energy facility.
The project, which employs a technology that’s being used in North America for the first time, produces 10 megawatts of electricity, enough to provide about one-third of the electricity needs of DC Water’s 157 acre Blue Plains wastewater treatment plant, the agency announced.
The thermal hydrolysis system, from Norwegian firm Cambi, takes the sludge that’s left over from the wastewater treatment process and converts it into methane, which is then burned to create electricity, according to the Washington Post. It works by heating and sterilizing those leftover solids and then mixing them up, Popular Science explains. That mash is put in a digester, where microbes consume it and release the methane.
And the solids that remain after all that are sterile and full of nutrients, and will be sold off as Class A biosolids, used as compost for plants, Popular Science adds.
The project is a “huge deal on so many fronts,” DC Water General Manager George Hawkins tells the Post. He adds that it represents a “public utility leading the world in innovation and technology,” and says both public and private water companies are lining up to see how the technology works, as it’s the largest thermal hydrolysis installation in the world.
The second largest thermal hydrolysis plant will be begin operating in Beijing in 2017, with a capacity of 134,000 tons per year. Cambi now has five contracts in China, which will treat approximately 1,200 metric tons of dry solids per day in Beijing, according to a release.
In 2013, Cambi was awarded a contract in Vigo, Spain, to process 22,000 tons of dry solids per year. The new plant will be the largest bio-filtration plant in Spain and one of the largest in Europe, according to a release.
DC Water is Washington’s biggest consumer of electricity, because of the huge amounts of energy needed to move water and sewage through its pipes, pumps and treatment plants. The new plant will save the agency about $10 million per year in enetry costs, Hawkins said. The utility expects to save an additional $2 million or so annually on treatment chemicals and $11 million annually in trucking expenses.
The project is being financed by tax-exempt bonds issued by DC Water and partially paid for by ratepayers. On Oct. 6, DC Water issued $350 million in tax-exempt, fixed rate bonds, including $100 million designated as green bonds. The green bonds are being used to finance the Clean Rivers project, a drainage system to prevent excess rainwater and sewage from discharging into the area’s rivers.
Last year, DC water issued $350 million in taxable green bonds, the first 100-year maturity ‘green century bond,’ to finance water projects. No previous green bond has carried a 100-year maturity, according to data provider Dealogic. It was also DC Water’s inaugural green bond issue and the first “certified” green bond in the US debt capital markets with an independent second party sustainability opinion, DC Water said at the time.
The Post also provided a detailed graphic explaining the process.