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The Impact of Internal Recycles on the Nitrifier Maximum Growth Rate
Author: Jose A. Jimenez, Henryk Melcer, Denny S. Parker and John R. Bratby
Date: 5/209
Nutrient Removal 2009 Conference Preprint

The nitrifier growth rate constant, A,max, is a critical parameter for design and performance of nitrifying activated sludge systems. Although many investigations have been devoted to study A,max, only a few have dealt with the effect of the reactor configuration on this important kinetic parameter. Bench-scale and full-scale trials were devised to study the impact of the internal mixed liquor recycle (IMLR) on the nitrifier growth rate constant. The nitrifier growth rate constant for an existing activated sludge plant was determined at different operational conditions using the High F/M test and by process model calibration. Overall, the results obtained during this study indicate that high IMLR values have a negative effect on A,max. Based on the results obtained during this investigation, a 15-percent decrease in A,max was observed at IMLR of 4Q or higher. It is surmised that at high IMLRs, the reactor behavior shifts from a plug-flow configuration to a quasi complete mixed configuration influencing either the species selection in activated sludge population or at least adaptation of specific species. These results have a tremendous impact on the design on activated sludge processes that incorporate IMLR for denitrification such as the Bardenpho, MLE, UCT and A2/O.