title: The effect of degree of recycle on the nitrifier growth rate.
abstract: The nitrifier maximum specific growth rate, mu(A),max, is a critical parameter for the design and performance of nitrifying activated sludge systems. Although many investigations studied mu(A),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 mu(A),max. Based on the results obtained during this investigation, a 15% decrease in mu(A),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.
authors.affiliation: Brown and Caldwell, 850 Trafalgar Court, Suite 300, Maitland, FL 32751, USA. Jjimenez@BrwnCald.com
authors.forename: Jose
authors.initials: J
authors.lastname: Jimenez
authors.forename: Henryk
authors.initials: H
authors.lastname: Melcer
authors.forename: Denny
authors.initials: D
authors.lastname: Parker
authors.forename: John
authors.initials: J
authors.lastname: Bratby
mesh_terms: D001419:Bacteria / Q000254:growth & development* / Q000378:metabolism*; D019149:Bioreactors; D009584:Nitrogen / Q000378:metabolism*; D059027:Recycling; D013696:Temperature; D013997:Time Factors
chemical_list: D009584:Nitrogen