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Title: Molecular characterization of filamentous bacteria isolated from full-scale activated sludge processes
Authors: Marrengane, Zinhle
Keywords: Bacteria--Identification;Sewage--Microbiology;Sewage--Purification--Biological treatment;Sewage--Purification--Activated sludge process;Sludge bulking;Sewage sludge;Biotechnology;Biotechnology--Dissertations, Academic
Issue Date: 2007
Abstract: Activated sludge flocs are responsible for flocculation, settling and dewaterability. It is important to maintain the growth off loc-forming bacteria for efficient sludge settleability and compaction for good quality effluent. Filamentous bacteria on the other hand are believed to provide rigid support network or backbone upon which floc-forming bacteria adhere to form stable activated sludge flocs (Wilderer et al., 2002; Ramothokang et al., 2003).

Filamentous bacteria can also be detrimental to the process when they outgrow floc-forming bacteria. Morphologically filamentous bacteria are at an advantage as they have
higher outward growth velocity and can extend freely to bulk liquid substrate.
Proliferation of filamentous bacteria causes foaming and bulking (Martins et al., 2004).

Although chemical alleviation measures to circumvent bulking are present, they are
symptomatic (Chang et al., 2004).

Eikelboom (1975) developed the first identification keys for the classification of
filamentous bacteria that is primarily based on morphological characteristics and
microscopic examination. Although very useful, this type of identification has its
limitations. For instance some filamentous bacteria can change morphology in response
to changes in the environment and although some of them can be morphologically similar
they may vary considerably in their physiology and taxonomy (Martins et al., 2004).

A vast number of filamentous bacteria are still very poorly understood which could be
due to the problems of cultivation due to their slow growing nature and maintenance of
cultures (Rossetti et al., 2006). This limitation necessitates a molecular approach to resolve the taxonomy of filamentous bacteria as it is a culture-independent technique which is highly accurate.

This project was undertaken to verify the identity of pure cultures of filamentous bacteria isolated previously through the application of molecular techniques. The 16S rDNA are conserved regions in bacterial cells and they can be extracted and specific nucleic acid fragments amplified. Denaturation gradient gel electrophoresis enabled the separation of fragments of identical length but different size and served as an indication of purity (Muyzer et al., 1993).
Description: Thesis (M.Tech.: Biotechnology)-Dept. of Biotechnolgy, Durban University of Technology, 2007 xviii, 143 leaves
Appears in Collections:Theses and dissertations (Applied Sciences)

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