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The City of Sheboygan owns and operates a regional wastewater treatment system that includes interceptor sewers, inverted river crossing siphons, pump stations, and an 18-mgd (56-mgd peak) treatment facility that serves seven communities across 60 square miles.
Donohue was retained to provide a planning study to evaluate the major collection system infrastructure and the wastewater treatment facilities. The treatment facility consists of headworks, primary clarifiers, enhanced bio-P activated sludge, secondary clarifiers, and chlorination/ dechlorination.
The City was interested in a design to replace their aged digester gas boilers that provide heat to four anaerobic digesters. The plant has two separate boiler systems, one for heating the digesters using digester gas and one for heating the plant buildings with natural gas. An interconnection existed between the two systems that allowed the building heating system to use a small portion of the heat available from the digester boilers to offset natural gas usage.
During a review of the piping systems associated with the digester boiler replacement, Donohue identified that an automatic means of providing heat from the digester boilers to the building system could be provided, which would be capable of transferring significantly more heat to the building with minor piping modification. These piping/control modifications were incorporated into the design and have been installed, resulting in significant natural gas savings for the plant. The automatic controls allow the two systems to be interconnected at all times to provide "free heat" from the digester boilers to the building system when required.
Environmental considerations for this project include the reuse of digester gas to heat plant facilities. The system is now able to more efficiently use the "free heat", conserving energy costs. |
