Client: City of St. Cloud, Minnesota

Location: City of St. Cloud, Minnesota

Donohue conducted an evaluation of resource recovery and energy efficiency opportunities at the St. Cloud Wastewater Treatment Facility (SCWWTF). The Resource Recovery and Energy Efficiency (R2E2) Master Plan Report developed sound energy practices, short- and long-term objectives, and implementation strategies related to energy efficiency and recovery. From a resource recovery perspective, the Plan developed a long-term biosolids strategy.

The SCWWTF is designed to treat an average-day flow of 18 million gallons a day (mgd) with a peak flow capacity of 44 mgd. The facility has full biological nutrient removal through a modified Johannesburg process. Solids are anaerobically digested and the Class B liquid biosolids are land applied.

Evaluation efforts focused on the project elements listed below.

• Energy Benchmarking – Established historical energy usage and biogas production.
• Energy Efficiency – Evaluated process modifications that enhance energy efficiency.
• Energy Production – Evaluated alternatives to produce beneficial forms of energy using existing biogas production, high-strength waste biogas production, and solar energy.
• Resource Recovery – Evaluated alternatives to harvest struvite-based phosphorus to reduce struvite-related maintenance concerns, enhance dewatering performance, and reduce the phosphorus content of the biosolids. Evaluated biosolids stabilization, handling, storage, and reuse strategies to define the future biosolids program and ensure energy efficiency and production improvements are consistent with this program.
• High-Strength Waste Program – Defined administration, operation, and infrastructure requirements for a sustainable and successful hauled-in waste program to enhance biogas production and reduce energy purchases.

After the R2E2 evaluation, the City retained Donohue to design biogas conditioning, utilization, and storage system improvements. Biogas conditioning uses a biofilter and activated carbon. A single engine generator will produce electricity and heat. The City also retained Donohue to implement the biosolids program improvements which include struvite harvesting, biosolids dewatering, Lystek biosolids processing, and liquid Class A biosolids storage. The Lystek process will be the first publically-owned installation in the United States.