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Donohue & Associates teamed with LHB Corporation to review the Facility Plan and design upgrades for the City of Chatfield, Minnesota's wastewater treatment plant. This project, which saved the City nearly $5 million, was a national finalist and received top honors, the Grand Award, from the American Council of Engineering Companies (ACEC) of Minnesota.
The Facility Plan was prepared by another engineering firm in 2003 to recommend improvements in anticipation of new NPDES permit limits that will enforce ammonia, totals suspended solids, and phosphorus restrictions. The new permit will limit ammonia levels during warm weather; however, the Facility Plan recommended an oxidation ditch that was designed to achieve these limits year-round. Since very large oxidation ditches must be constructed to achieve nitrification (ammonia removal) in cold weather, Donohue/LHB reduced the size of the ditch to allow for nitrification only during summer months.
The existing Facility Plan, which projected construction costs for upgrades to be approximately $11 million, included a new Carrousel-type oxidation ditch to work in parallel with the existing trickling filter. After careful review, Donohue/LHB determined that a single three-ring oxidation ditch would produce the same, if not better effluent results without the need to maintain the existing trickling filter. In addition, use of the three-ring oxidation ditch eliminates the need for primary clarifiers, which freed up space for a maintenance area and ultimately saves in operation and maintenance costs.
ACEC of Minnesota annually recognizes engineering projects that employ creative and innovative techniques that serve to advance the engineering field. This project was one of only nine to receive this award.
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