Reducing Wastewater Sludge Pathogens Using Heat Treatment

by Mark Kennedy, (M.ASCE), South Dakota State Univ, Brookings, United States,
Kondapalli Reddy, South Dakota State Univ, Brookings, United States,
Lyle Johnson, (M.ASCE), South Dakota State Univ, Brookings, United States,

Document Type: Proceeding Paper

Part of: Critical Issues in Water and Wastewater Treatment


The feasibility of using waste heat to reduce pathogen densities in wastewater sludge at a municipal wastewater treatment plant was investigated. Two modifications to an existing two stage mesophilic anaerobic digestion process were studied, 1) pasteurization of primary digester sludge prior to secondary digestion and 2) operation of the second stage digester at thermophilic temperatures. Both options for using waste heat resulted in a sludge which met Class A criteria with respect to fecal coliform and salmonella sp. densities. Ascaris ova were also inactivated. Destruction of volatile solids was greater than current digester operation and digested sludge did not support the regrowth of bacteria during subsequent storage. Analysis of heat requirements revealed that waste heat generated during summer operation of the anaerobic digesters was more than sufficient to support thermophilic operation of the second stage digester.

Subject Headings: Anaerobic processes | Waste treatment | Heat treatment | Sludge | Wastewater treatment plants | Bacteria | Pathogens

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