City of Monticello Sludge Pasteurization Project

Location:  Monticello, Minnesota
Year Completed: 1999
Deliverables: 6MMBTU/hr waste water pasteurization heating system

Project Overview


In view of the environmental legislation passed by the US Congress, there is pressure on the US wastewater treatment facilities to address the problem of discharge of potentially harmful pathogens present in the treated municipal liquid waste back into the environment.

The traditional digestion methods do not produce temperatures high enough to destroy the pathogenic bacteria present in the sludge. Higher temperatures are required for effective pasteurization to produce the Class “A” biosolids. Consequently, all new wastewater treatment facilities or modernization projects have to look for new technological solutions to address this requirement.

The traditional method of dealing with bacteria is to heat the sludge in a heat exchanger using a steam or hot water boiler. Upon reaching the temperature of 158o F (70oC) sludge is stored for a minimum period of 30 minutes to achieve full pasteurization.

The City of Monticello, Minnesota undertook a modernization project of the Monticello Wastewater Treatment Plant that serves the local town and two food processing plants.

HDR Engineering’s Minneapolis office was retained as project consultant. Part of the plant modernization included a sludge pasteurization system. Inproheat was involved in the development of the process design concept using proprietary submerged combustion (SubComTM) technology.

Subsequently, after a bidding process, Inproheat was awarded a contract by the project’s prime contractor Adolfson & Peterson of Minneapolis to supply a sludge pasteurization system for the Monticello WWTP.