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St. Cloud, Minnesota

2018 ACEC Minnesota Grand Award

St. Cloud’s Resource Recovery and Energy Efficiency project received an Engineering Excellence Grand Award from the American Council of Engineering Companies (ACEC) of Minnesota. The award was presented to Donohue & Associates and the City of St. Cloud.

St. Cloud is a leader in innovative, cost-effective, and sustainable practices. Donohue collaborated with its wastewater treatment facility to produce a Resource Recovery and Energy Efficiency Master Plan that is guiding the City along its path to energy neutrality and greater resource recovery. This path includes the design of recently constructed Energy Efficiency and Biofuel Recovery improvements.

Before the project, the City's wastewater treatment facility burned off a large fraction of biofuel released during the anaerobic digestion process. The Master Plan improvements allowed this renewable energy to be captured by efficient biofuel conditioning equipment and a biofuel-driven engine generator would convert the biofuel to electricity and heat. The electricity powers wastewater treatment processes and the heat is used to heat buildings and the anaerobic digestion process. This unique biological desulfurization system, the first municipal installation in Minnesota, cleans biofuel.

The goal was to reduce City-purchased energy by 25% within 5 years, by 50% within 10 years, and by 75% within 20 years. Donohue developed a plan to address the issue by developing sound energy practices, short- and long-term objectives, and implementation strategies related to energy efficiency, energy production, nutrient recovery, and biosolids reuse.

The design incorporated high-strength waste receiving and co-digestion, biofuel storage and conditioning, and electrical energy generation into existing facilities while maintaining plant operation. Complex electrical coordination synchronized the plant’s power grid, generator, back-up generator, and on-site solar energy generation.

April 11, 2017 will forever be known as “Energy Independence Day;” the first day the wastewater treatment facility produced 100% of its required energy and achieved Net Zero Energy status.  This is the first for municipal wastewater in Minnesota. The facility produces more than 90% of its required electricity on average annually, exceeding purchased energy reduction goals 17 years ahead of schedule.