| This research integrates experimental, modeling, and molecular tools to study of the kinetics and ecology of nitrification in activated sludge. Experimental work includes the design and operation of two reactors, a chemostat and a sequencing batch reactor (SBR), that provide well-controlled experimental data. The mathematical model is based on the multispecies formulations of Furumai and Rittmann (1992), but contains important modification to handle denitrification, bioaugmentation, nonsteady-state conditions, and a membrane separator. Oligonucleotide probes are applied so that the nitrifying bacteria can be measured independently from the larger heterotrophic populations. The modeling and molecular tools also are applied to pilot-scale membrane bioreactors (MBRs) operated by Societe Lyonnaise des Eaux, France, and to a laboratory chemostat designed to test bioaugmentation.; Chemostat experiments demonstrate that the model represented all the key phenomena. Among the most important insights are that the soluble COD is dominated by soluble microbial products, which are strongly affected by the influent Kjeldahl nitrogen. Also demonstrated is simultaneous denitrification with nitrification, particularly when the D.O. is low.; For the SBR, anoxic-aerobic cycling gives excellent soluble-COD removal, nitrification, and denitrification when the D.O. is {dollar}ge{dollar}2 mg/L in aerobic periods and the SRT is {dollar}ge{dollar}10 days.; Mathematical modeling successfully represents the performance of the MBRs treating municipal wastewater. The model shows that the effluent soluble COD is mainly controlled by the biomass-associated products (BAP) fraction, but that about 30% of the BAP is retained by the ultrafilter. Introducing an anoxic period to the MBR system reduces the costs of sludge handling and O{dollar}sb2{dollar} supply, and reduces total N in the effluent, but increases NH{dollar}sb4sp+{dollar}-N leakage.; Bioaugmentation studies demonstrate that bioaugmentation of stressed systems can restore good performance, as long as the dose of bioaugmented microorganisms is large enough. In case of high stress, almost all the nitrifiers present in the system must be bioaugmented.; Oligonucleotide probe NSO 1225 is effective for assaying ammonia-oxidizers. However, probe NB 1000 (for nitrite oxidizers) systematically underestimates the amount of nitrifiers, probably because it does not hybridizes to uncharacterized strains that are important to the ecology of these systems. |
