The DC Water Waste to Energy (W2E) project started producing electricity this September using its new solids handling processes. The project is located at the Blue Plains Advanced Wastewater Treatment Plant. The plant currently treats about 300 million gallons of raw sewage a day from the District of Columbia and from counties in Maryland and Virginia. The facility has a power output of 10 MW, which is enough to power one third of the Blue Plains Advanced Wastewater Treatment Plant.
This project is a major public investments in solids processing. Its price tag is around $470 million and took four years to build. The project’s construction included a dewatering building, 32 thermal hydrolysis vessels, four anaerobic digesters capable of holding 3.8 million gallons of solids each, and three turbines the size of jet engines. The plant expects to save $10 million on energy costs, $2 million on treatment chemicals, and an additional $11 million annually in trucking expenses for solids removal.
Prior to breaking ground in 2011, DC water conducted over a decade’s worth of research. Eventually the agency found the project would best be served using the CAMBI thermal hydrolysis process.
Thermal Hydrolysis Technology
The W2E project is the first in North America to use thermal hydrolysis technology. This technology application from Cambi is the largest such facility in the world. Thermal hydrolysis is a two stage process where a combination of high-pressure and heat are used to 'cook' sewage sludge. In the second stage the sludge is quickly sent to a different chamber where rapid decompression occurs. The result is sterilized sewage. But mutually important, this feed is digestible, and an increased amount of methane gas can be produced compared to standard digestion. Methane extracted in the process is sent to power electric generators, for which the agency has installed three 5 Megawatt turbines. Steam generated in the process is also reused for the CAMBI system.
Class B to Class A Biosolids
Before the W2E project, Blue Plains trucked Class B biosolids to local agricultural facilities. 60 truckloads of the material left the plant daily. The trucks traveled to farms in Virginia, which was not only pricey, but resulted in the emission of much carbon from diesel fuel usage.
The new facility will cut the amount of solids leaving the plant for land application in half and reduce the distance some of the sludge travels. What does leave the plant is a higher quality, class A biosolids. Class A biosolids have been treated in order to kill nearly all pathogens. This product can be applied to land in an urban area as well as farmland in the surrounding area.
Most exciting for the biosolids profession is the prospect of high quality biosolids being deployed in landscapes in and around DC. The biosolids leaving Blue Plains may one day be on shelves of garden centers and home improvement stores throughout metropolitan Washington. To help support this prospect, a study is underway, funded by the Water Environment Research Foundation. DC Water is part of a team looking into into the preparation of urban soil products using this new biosolids material and into successful marketing strategies for biosolids-based products. You can learn more as this program develops by visiting our Facebook page for this research, High Quality Biosolids.