HDR was the lead engineering firm for the expansion of the Empire Wastewater Treatment Plant in Dakota County, Minnesota. Owned and operated by the Metropolitan Council Environmental Services, the plant had a capacity of 12 mgd. An expansion of the plant helped meet growth in the service area as well as new permit requirements.
The expansions, which include a new biological nutrient removal system, doubled the capacity. The new facilities include primary clarifiers, aeration basins, secondary clarifiers and ultraviolet disinfection.
Return flows from solids processing are managed to mitigate the impact on the biological nutrient removal process. This design incorporated existing facilities into the new treatment process to minimize construction costs.