MICROBIAL SUCCESSION IN ACTIVATED SLUDGE:ECOLOGICAL PRINCIPLES LINKCOMMUNITY DIVERSITY AND OPERATING PERFORMANCE

摘要

Heterotrophic biomass in activated sludge wastewater treatment systems often isdescribed according to the kinetics of substrate utilization. Typically, two “groups” ofmicroorganisms are described, namely floc-formers and filaments. Previous studies haveattempted to correlate bioreactor operation with the relative abundance of these two“groups” of microorganisms. For example, plug flow bioreactors with high substrateconcentrations have been shown to favor floc-formers (e.g., Monod-type r-strategists)while completely mixed bioreactors with low substrate concentrations have been shownto favor filaments (e.g., Monod-type K-strategists). The objective of this study was todetermine if additional factors impact the diversity of the microbial community inactivated sludge bioreactors. To meet this objective, we have begun to systematicallyexplore correlations between the relative abundance of representative modelmicroorganisms and bioreactor operating strategies. For these studies, fluorescence insitu hybridizations with 16S rRNA-targeted oligonucleotide probes have been used toidentify and enumerate Acinetobacter spp. in samples from laboratory-scale activatedsludge wastewater treatment systems. Preliminary results suggest that long idle stages, aswould be expected in secondary clarifiers operated with significant sludge blankets,correlate with an elevated relative abundance of Acinetobacter spp. This elevatedrelative abundance appears to be independent of the initial concentration of growthlimiting substrate in the bioreactors (i.e., long idle stages result in selective enrichment ofAcinetobacter spp. in both plug flow and completely mixed bioreactors). Based uponthese results, we hypothesize that the inclusion of long idle stages in bioreactor operationprovides a selective pressure that dictates the composition of the microbial communityindependent of the initial concentration of growth limiting substrate. These results havebroad implications for biological wastewater treatment – suggesting that the current two“groups” of heterotrophic microorganisms may be insufficient to capture the essentialdiversity of microorganisms in activated sludge bioreactors.