In 2008, Maryland’s largest water utility, WSSC Water—formerly known as the Washington Suburban Sanitary Commission—began exploring ways to improve the quality of its biosolids from five of its wastewater treatment facilities. Local landfills were increasingly charging more or sometimes refusing to accept the treated sewage sludge known as Class-B biosolids. The materials have limited applications and cannot be used in public spaces as fertilizer. “Disposal has gotten more and more expensive and more regulated over the years,” says Theon Grojean, WSSC Water’s division manager for facility design and construction.
WSSC Water, with help from AECOM and other consultants, conducted an evaluation of a variety of potential methods to produce Class-A biosolids, which are safe for use as fertilizer or as composting material. After the review, WSSC Water decided to install one of the first thermal hydrolysis process (THP) units in the U.S. at its Piscataway treatment plant in Accokeek, Md. The commission also is adding an energy recovery system that uses biogas produced through the THP process to provide enough pipeline-grade natural gas to power the plant and potentially earn energy credits with Montgomery County, Md.