Donohue’s innovative approach to increasing plant capacity at the City of Hutchinson’s wastewater treatment facility (WWTF) earned an ACEC Minnesota Engineering Excellence Grand Award and ACEC National Finalist.

Prior to the upgrade, the City’s WWTF was operating at or above capacity for biological oxygen demand (BOD), total suspended solids (TSS), and ammonia nitrogen; additionally, future new phosphorus and mercury limits necessitated upgrades.

The existing treatment train included two oxidation ditches and clarifiers. Conventional methods of increasing capacity were evaluated, including adding a third oxidation ditch and final clarifier, but were eventually rejected due to large footprints and considerable operator control. Donohue also explored converting the entire plant to a Membrane Bioreactor process, but the hefty price tag associated with such a conversion proved to be prohibitive. The final solution, an MBR system that runs in parallel to the existing treatment train, combines modern and conventional technologies to maximize effluent quality and minimize costs.

This solution is the first in the Midwest and one of just a handful built across the US. Two-thirds of the plant flow goes to the existing oxidation ditches and final clarifiers, while the remaining one-third is sent to the new MBR process. The effluent is then blended, resulting in superior quality. In order to be eligible for low interest funding, the facilities were designed in less than 10 weeks.

Randy Devries, Director of Water/Wastewater Operations for the City, said about the project, “Donohue worked closely with us to develop a creative, cost-effective solution that has surpassed our expectations. As a result of this project, we have seen a tremendous increase in all aspects of effluent quality. The plant is incredibly clean and easier to operate and maintain.”