Donohue & Associates and the City Superior, Wisconsin, received the Best of State Award in the 2011 ACEC Wisconsin Engineering Excellence competition. The award recognizes a unique 20-year facility plan that utilized an innovative nitrification process to meet new effluent ammonia limits.

Donohue and LHB Corporation used an interactive evaluation process and process modeling to develop an alternative to nitrify the ammonia-rich side stream coming from the anaerobic digesters. This solution, which has only been used at a handful of facilities in the US, works by exploiting the warm temperature of the side stream to achieve year-round nitrification in only the flow with the highest content of ammonia. This solution would have allowed the City to reliably nitrify enough flow year-round to meet permit limits while reducing capital and operating costs, a savings which translated to more than $26 million compared to the baseline alternative.

But we did not stop there. When modeling the expected performance of this low cost alternative, it became apparent that the City would likely benefit from monthly rather than seasonal effluent ammonia limits. The City worked with WDNR to develop new limits that are representative of the City’s specific receiving waters. The City received a significant relaxation in the limits while still protecting the valuable waters of Lake Superior. As a result, a new, lower cost alternative could be implemented that saved the City approximately $28 million in capital cost and $300,000 in annual operating costs.