PERFORMANCE OF FIXED-FILM MEDIA INTEGRATED IN ACTIVATED-SLUDGE REACTORS TO ENHANCE NITROGEN REMOVAL

Nitrification and denitrification were evaluated in multiple CSTR cont inuous flow fixed film systems at 12 degrees C. Three systems were ope rated with three types of media installations and a fourth as a contro l without media. The media configurations evaluated included: (i) fram e mounted fine pore sponge media supported on wires; (ii) free floatin g fine pore sponge media; and (iii) fixed location fr,une mounted rope media (ringlace). The pore size for sponge media was 14 pores per cen timeter. Each system included a two-cell anaerobic zone with 17 percen t of total volume, two-cell anoxic zone with 17 percent of total volum e, and a three-cell aerobic zone with 64 percent of total volume. The multi-cell configuration was used to maximize kinetics of removal with suspended growth biomass and evaluate improvements in nitrogen remova l beyond the levels achieved with suspended growth. At the optimum loc ation (aerobic cells 1 mid 2), the nitrification in cells containing f ree-floating sponges was 143 percent of the control at aerobic MCRTs o f 3.1 and 3.4 days, with 3.5 percent media volume to cell volume. The nitrification with rope media was 136 percent of the control ill middl e third of the aerobic zone. Removals with ringlace were poorer in the first aerobic cell operating at higher COD levels, and in the third a erobic cell which did not contain sufficient biofilm growth at low lev els of GOD. Nitrification was 14 percent higher in Systems 1 and 2 wit h fixed and free floating sponges, respectively, and 8 percent higher in System 3 (ringlace) when all systems were spiked with 20 mg/L addit ional ammonium over a 24 hour period. Optimizing location of the media , with higher density of media at locations where adequate COD and amm onium-N are available for biofilm growth increase nitrification on med ia. Studies in full scale systems show that COD and ammonium-N concent rations at downstream locations in the activated sludge basin increase during peak flows and with step feed of wastewater. This helps increa se biofilm growth and improve nitrification on the media downstream lo cations. Denitrification observed in the aerobic cells of the fixed fi lm systems was in excess of the control. All aerobic cells were operat ed at D.O. levels in excess of 6.0 mg/L. The fraction of total denitri fication under aerobic conditions was 0.0 in the control as compared t o 0.14 to 0.24 with ringlace media and fixed sponge media, respectivel y, at an aerobic MCRT 3.1 days. Fraction aerobic denitrification in al l systems increased with an increase in MCRT of suspended growth - to 0.21 in the cotrol and 0.35 and 0.39 with ringlace and sponges, respec tively, at aerobic MCRTs of 3.4 to 7.7 days.