Filamentous organism bulking in nutrient removal activated sludge systems: Paper 8: The effect of nitrate and nitrite

Abstract

The presence of nitrate (NO3-) and nitrite (NO2-) has a significant effect on the proliferation of low F/M filamentous organisms in nitrogen (N) and nutrient (N and phosphorus-P) removal activated sludge systems. In experiments in which the concentrations of NO3-and NO2-were manipulated in the 2nd anoxic reactor of a modified University of Cape Town (MUCT) nutrient removal system, either by addition of ammonium to the influent or by dosing NO 3-or NO2-to the 2nd anoxic reactor, the extent of low F/M filamentous organism proliferation could be controlled, as measured by the diluted sludge volume index (DSVI). With a sufficiently high TKN/COD ratio (> 0.10 mgN/mgCOD) in the influent, or by dosing NO 3-and NO 2-at a level at which the denitrification potential of the anoxic zone was exceeded by the NO3-or NO2-load, the DSVI increased from values less than 100 m/G6C/g to values greater than 150 m/G6C/g in periods of between 3 and 5 sludge ages. It could not be determined which of NO3-or NO2had the most significant effect on filament proliferation.

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