Wastewater Treatment Facility Expansion Update
Completion Date Delayed
(Article by Jennifer Svennes, Nero Engineering)
The focus of the Owatonna Wastewater Treatment Facility (WWTF) project has moved from the liquid processes to the solids processes in recent months.
The solids removed from the liquid get treated by thickening, anaerobic digestion and dewatering. The thickening process removes water, which gets recycled through the liquid treatment and increases the solids concentration before the sludge, is sent to the anaerobic digestion process. Increasing the solids concentration before digestion allows the volume of the digester to be smaller. In Owatonna’s case, it contributes to the existing digester tanks being adequate volume for the next 25 years even though the loading is expected to nearly double in that time. Anaerobic digestion stabilizes the solids so they are safe for land application and also creates biogas. After digestion, more water is removed from the solids through the existing dewatering process and then hauled to storage before land application.
This project to update Owatonna’s WWTF includes a new solids thickening process housed in a new building. Rotary drum thickeners have been installed and recently started up. The startup of this equipment allows the existing dissolved air flotation thickening process to be taken offline so the building modifications for the biogas treatment system and electrical room in the Digester Treatment Complex (DTC) can begin. Once the electrical gear in the DTC is in place, the refurbished anaerobic digesters can be brought online along with other equipment located in the DTC.
Due to electrical equipment delays, the project needs to be extended by about seven months. The new substantial completion date for the project is January 2026. The good news is the last of the equipment that has been delayed is expected to be onsite by the end of this month. The team has done its best to minimize project delays by finding ways to temporarily power the equipment when feasible and by being flexible in the construction sequence.
The Owatonna WWTF staff deserve a huge amount of credit for being flexible and learning how to operate and maintain new processes while maintaining treatment throughout the entirety of construction.
The City Council approved an extension of the agreement with Nero Engineering and two change orders at its March 18 meeting to support the continuation of this project.