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“CLASS A” DIGESTION: RETOOLING AN OLD PROCESS TO FULFILL A NEW OBJECTIVE

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Abstract:

European treatment works generally opt to add-on pre-pasteurization when production of pathogen-free biosolids is desired. In the United States, publicly owned treatment works (POTWs) are more interested in achieving pathogen reduction within the anaerobic digestion process or by supplementing digestion with downstream processing such as heat drying to produce a more esthetic product for distribution and marketing.

Demonstrating that advanced digestion processes are equivalent to a Process to Further Reduce Pathogens (PFRP) has proven to be a daunting task. Therefore, a growing number of POTWs are undertaking pioneering projects aimed at satisfying the definitional, time-temperature requirements for Class A under the 503 regulations. These include creative operational control schemes for thermophilic digestion, temperature phased anaerobic digestion (TPAD), and two-phase digestion systems.

This paper focuses on meeting the definitional requirements for Class A pathogen reduction and the heating and heat recovery challenges identified to-date by system designers in implementing these projects. Potential solutions are suggested.

Document Type: Research Article

DOI: https://doi.org/10.2175/193864702784247701

Publication date: 2002-01-01

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