Role of microbial community dynamics and the extracellular matrix in formation and instability of microbial structures in biological wastewater treatment systems
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The structural, physiochemical, and microbial properties of biofilms, flocs, and granules during the formation and instability of these microbial structures were studied. Specifically, the composition of extracellular polymeric substances (EPS) and microbial community dynamics were observed during: (a) formation of granules by modifying the operational conditions for rapid granulation in an integrated fixed-film – sequencing batch reactor (IF - SBR) system, (b) aerobic granule development with transient filamentous bulking, and (c) biofilm sloughing in an IFAS system. The thesis arose from the observations of the dynamic nature in which these structures developed and changed while operating IF - SBR. Biomass from IF - SBR could be differentiated into more and less hydrophobic fractions and the physicochemical properties and changes in EPS were associated with periodic sloughing of the biofilm from IF - SBR carriers. It was found that sloughing did not lead to biomass loss from the bioreactors and the resulting suspended biomass and flocs that had enhanced settleability. Coupling granulation technology with an IFAS system was an interesting development that improved the capacity and efficiency of wastewater treatment. Rapid granulation was observed with oxic/anoxic/oxic conditions in the IF - SBR system where Rhodocyclaceae and Comamonadaceae populations (known for denitrification) were predominant. During granulation, a microbial community was selected with a predominant bacterial group, which produced a protein rich extracellular matrix for formation of compact granules. The lysis of dominant microbial population in aerobic granules resulted in transient granule instability; however, the microbial community was capable of self-remedy to restore the granular structure after an instability phase. In the IFAS system, microcolonies with a higher polysaccharide content and dead cells resulted in biofilm sloughing. It was observed during the study that apparently distinct microbial structures (biofilms, flocs and granules) are pleomorphic microbial aggregates. The Identification of hydrophobic characteristics of bacteria and the extracellular adhesins expressed by the bacteria have a potential to improve our understanding about microbial interaction. The understanding about the microanatomy of biofilms, flocs and granules will facilitate to engineer stable microbial structures.
URI for this recordhttp://hdl.handle.net/1974/15355
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