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With increased public scrutiny and growing local regulation of land application of Class B biosolids, some utilities have become concerned about continued reliance on this practice. Consequently, they are exploring options for improving solids treatment to achieve Class A or similar enhanced treatment standards. With composting losing much of the popularity it held in the 1980s, much of the focus for achieving Class A stabilization in the United States (U.S.) has been on advanced digestion, thermal drying or chemical stabilization. Advanced digestion to meet Class A requirements has been implemented by utilities which have a successful liquid or dewatered cake land application program and desire to continue this practice. Thermal drying has been used by utilities seeking an enhanced product to maximize distribution and marketing opportunities. In contrast to U.S. practice, European counterparts seeking to enhance digester performance have embraced more innovative technologies, including pasteurization and thermal hydrolysis, to meet enhanced treatment standards.

This paper will review the drivers, the key design elements, and the results to-date of four recent projects in the U.S. and Europe, operating different processes aimed at meeting Class A performance standards. As illustrated by these projects, existing plant processes and site configuration, as well as local practices, play a large role in determining which process is most advantageous for a particular facility.

Document Type: Research Article


Publication date: 2006-01-01

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