The Effect of Degree of Recycle on the Nitrifier Growth Rate
Abstract:The nitrifier maximum specific growth rate, μA,max, is a critical parameter for the design and performance of nitrifying activated sludge systems. Although many investigations studied μA,max, only a few have dealt with the effect of the reactor configuration on this important kinetic parameter. Bench- and full-scale trials were devised to study the effect 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 food-to-microorganism ratio (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 μA,max. Based on the results obtained during this investigation, a 15% decrease in μA,max was observed at an 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-mix configuration, influencing either the species selection in activated sludge population or at least the adaptation of specific species. These results have a tremendous effect on the design of activated sludge processes that incorporate IMLR for denitrification, such as the Bardenpho, Modified Ludzack-Ettinger (MLE), University of Cape Town (UCT), and Phoredox or anaerobic‐anoxic‐aerobic (A2/O) processes.
Document Type: Research Article
Affiliations: Brown and Caldwell, Maitland, Florida
Publication date: 2011-01-01
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