THE PERFORMANCE OF IFAS MEDIA IN ANOXIC ZONES OF BNR SYSTEMS

This research project investigated the addition of fixed-film media (BioWeb®) into the anoxic zones of pilot-scale, biological nutrient removal (BNR) activated sludge systems, both with and without media in the aerobic zones, in an effort to evaluate the effects of fixed-film media integrated into the anoxic zones of anaerobic-anoxic-aerobic BNR systems. Three identically sized, continuous flow, UCT configuration systems were operated in parallel at a hydraulic retention time (HRT) of 13 hours, using the same wastewater influent. Two of the systems were operated as integrated fixed-film activated sludge (IFAS) systems while the third was maintained as a control without media. It was possible to maintain enhanced biological phosphorus removal (EBPR) in the anoxic IFAS systems as long as the COD/TP ratio of the wastewater was favorable, but media in the anoxic zone decreased the amount of EBPR. The amounts of biomass that developed on the anoxic media were only 38 to 50% of the growth on the aerobic media of the same system. However, media in the anoxic zones not only increased denitrification in the anoxic zone, but also increased it in the following aerobic zone containing no media. A very consistent determination was that placement of media in the anoxic zone significantly reduced total system biomass production, from 8.5 to 18.3 %.