Enhanced nitrogen removal in activated sludge with fixed biomass

Alternative methods for upgrading activated sludge plants by improving removal of nitrogen were investigated at pilot and full scale. These included submerged elements in the aeration tank to provide a fixed biomass (BIOFIX system), contact stabilization to maintain higher sludge age in the same tank volume, and addition of submerged biofilter packing as a tertiary treatment system. The results confirmed that the installation of biomass support media in the aeration tank could increase carbon removal and nitrification by reducing the F/M ratio and increasing sludge age. The contact stabilization process also improved nitrification and denitrification and, when this mode of operation was combined with the use of submerged biomass carriers, a reduction in nitrogen content of 50 per cent could be achieved with detention periods of 4 hours. There is a bibliography of 33 references.