IFAS BNR FULL-SCALE DESIGN AND PERFORMANCE CHALLENGES

Wastewater treatment plants across the United States are faced with increasingly more stringent discharge limitations on phosphorus and nitrogen. These facilities are now challenged to find an economical means to upgrade treatment in order to meet new limitations. The reasons for these limitations are numerous and include issues such as eutrophication in water bodies such as Chesapeake Bay, Long Island Sound and the Gulf of Mexico particularly at the discharge of the Mississippi River, implementation of TMDLs, water reservoir protection from nutrient overload, and reuse regulations which protect groundwater from nitrate contamination. Many wastewater treatment plants, particularly those in the coastal regions, were originally built as carbonaceous removal activated sludge plants. Implementing nutrient control at these plants normally implies significant aeration basin expansion to achieve the sludge age required for nitrification.In addition to the need for capacity expansion, the City and County of Broomfield Colorado was challenged with pending nutrient limitations. A study of potential options revealed that implementation of a hybrid system through conversion of the existing aeration basins to integrated fixed-film activated sludge using suspended plastic carriers, coupled with the addition of upstream anaerobic and anoxic basins, was the most economical solution when compared to three other alternatives.An on-site pilot study was conducted to confirm the design parameters and conditions which would yield reliable nitrogen control. Primary objectives of the four-month pilot study were to verify reliable winter nitrogen control at a reduced suspended sludge age, quantify nitrification rates, document impacts of residual dissolved oxygen levels on nitrification performance, determine the degree of simultaneous nitrification and denitrification in the aerobic zone, and investigate the sludge and attached-growth characteristics of the integrated fixed film activated sludge system. This paper presents the results of the pilot study and provides discussion of the main design considerations gleaned from this study. Construction of the full-scale facilities is underway and the first of two IFAS treatment train is expected to be in operation by the end of the year 2002.