Rochester, Minnesota

The City of Rochester Wastewater Reclamation Plant (WWRP) serves the residential, commercial and industrial residents of the City of Rochester, Minnesota. The city has a population of approximately 100,000 people, and the plant has the capacity of processing approximately 24 million gallons per day (MGD) of sewage and wastewater. The incoming waste stream (influent) is pumped to a higher elevation with the plant’s preliminary, primary, secondary, and advanced treatment processes fed by gravity flow. The solids handling system utilizes anaerobic digestion which produces the treated solids that are trucked from the facility as well as the biogas that is stored and utilized on-site as fuel for both heating and electrical generation. The processed water goes through a final chlorination stage and is then pumped to a local river.

This facility was an early adopter of CHP technologies installing its first system in 1982. In 2002, a two phase project was initiated to upgrade the existing CHP system, and in 2008, the project was completed when the second original engine was replaced with a second new 1,000 kW dual fueled engine generator with heat recovery. The installed capacity of 2,000 kW is more than sufficient to handle the amount of biogas generated by the digesters today. All the electricity generated by the CHP system is utilized onsite to off-set the base load electrical requirements of the facility. This application is an excellent example of the flexibility for CHP to satisfy numerous energy needs: the system provides adequate facility emergency power; it uses all treatment process biogas to heat digesters during extreme temperature conditions; and it maintains a dual-fuel capability for plant operations.