Filamentous Foaming in Activated Sludge Systems: A Study Combining Molecular and Engineering Approaches

257 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2000.Foaming in activated sludge systems is characterized by the formation of a thick, chocolate brown-colored scum that floats on the surface of aeration basins and secondary clarifiers. These viscous foams cause various operational problems, and have been associated with the presence of filamentous mycolic acid-containing actinomycetes (mycolata) and "Microthrix parvicella ". However, the relationship of filament populations to foaming incidents is not fully understood. This is in part due to the limitations of morphology- and culture-based methods in analyzing microbial populations in activated sludge. In contrast, the use of ribosomal RNA (rRNA)-targeted oligonucleotide hybridization probes allows for the reliable identification and quantification of specific microbial populations. Group-, genus-, and species-specific small subunit rRNA-targeted oligonucleotide probes for the mycolata, Gordonia, and Gordonia amarae, respectively, were developed, and probes specific for "M. parvicella " were characterized. Membrane hybridizations and a new quantitative fluorescence in situ hybridization method for estimating Gordonia mass were used to follow shifts in population of Gordonia and "M. parvicella" and other major microbial groups in activated sludge before and during a seasonal foaming incident in a full-scale plant. The rRNA and volatile suspended solids (VSS) percentages of Gordonia (but not "Microthrix parvicella" increased during foaming, and these values decreased as the foam disappeared. Differences in rRNA and VSS levels indicated that a significant fraction of the filaments in foam was not actively growing. This finding implies that: (1) the trigger, or initiation event for foaming, is the important phenomenon, and (2) methods to control filament growth after foaming has occurred may not be beneficial, as even inactive cells contribute to foaming. Batch tests indicated the existence of formation and stability thresholds. The formation and stability thresholds corresponded to filament levels of 2 x 108 mum/ml and 1 x 109 mum/ml, respectively. These values were verified in full-scale and lab-scale reactor studies. These results have provided new insights on foaming phenomena, and have been integrated into a conceptual model of filamentous foaming, which analyzes the ecological strategies of foam-forming filaments in activated sludge, and proposes a relationship between filament levels and foaming.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD