Many of us are tired of the grandstanding and platitudes that come from Washington, D.C., and have long been resigned to the sad fact that the nation’s capitol is often full of crap. But literally, any city home to 650,000 people is going to flush plenty of crap down the drain. Now the greater D.C area is putting some of that crap to good use, as in harvesting it to generate 10 megawatts of clean energy to lower a local wastewater treatment plant’s electricity bills.
Built at the cost of $470 million, this (mostly human) waste-to-energy plant will provide one of metropolitan Washington’s water utilities with a new way to meet a third of its total power needs, or enough to electrify 10,500 homes. The Blue Plains Advanced Wastewater Treatment Plant, which D.C. Water claims is the largest such facility in the world, provides wastewater treatment services to approximately 2 million people in D.C. and the surrounding area. More than 350 million gallons of sewage pass through this wastewater plant daily. And while the Blue Plains plant is seen as an exemplary wastewater treatment center, the processing of all those toilet flushes consumes its fair share of electricity.
This waste-to-energy project started construction in 2011 after a decade of studies, and finally launched last month. According to D.C. Water, the plant incorporates the use of a Norwegian technology, a CAMBI thermal hydrolysis process, which is now being used in North America for the first time at Blue Plains. Without getting into too deep a technological or scatological explanation, this thermal hydrolysis system incorporates high heat and pressure to “pressure cook” any solids remaining after the final stages of the plant’s wastewater treatment process.
These solids, in turn, undergo an anaerobic digestion process, which creates methane that can be captured in order to generate electricity. Three large turbines, each the size of an airliner jet engine, anchor this facility. Along with the turbines, this plant also includes a dewatering plant, 32 hydrolysis vessels and four concrete anaerobic digesters that stand 80 feet (24 meters) tall.
In addition, this waste-to-energy process creates biosolids that can be used as compost or topsoil. D.C. Water is evaluating whether this product can be brought to market, which would certainly create a new revenue stream that could help pay off the project’s costs (inquiries made to D.C. Water about the expected ROI were not returned, but the Washington Post quotes cost-savings to D.C. Water at running about $10 million annually). In the meantime, this byproduct is being used as compost in urban gardens and infrastructure projects throughout the D.C. area.
The project’s price-tag certainly raises questions about whether such innovations in clean energy are worth the investment. But as more cities search for ways to move toward a zero-waste and low-carbon economy, D.C.’s new approach to waste management could offer municipalities a case study on how to cope with a growing population, adapt to aging infrastructure and discover new ways in which to keep energy costs low.
Image credit: EPA