Microbial Biotechnology |
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Biofilms |
Electronic Journal of Biotechnology ISSN: 0717-3458 |
Vol.
11 No. 2, Issue of April 15, 2008 |
© 2008 by Pontificia Universidad Católica
de Valparaíso -- Chile |
Received August 28, 2007 / Accepted December 6, 2007 |
DOI: 10.2225/vol11-issue2-fulltext-12 |
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Visualisation of the microbial colonisation
of a slow sand filter using an Environmental Scanning Electron Microscope
Esther Devadhanam Joubert*
Department of Environmental Sciences
Skinner Street Campus
University of South Africa
P O Box 392, 0003
South Africa
Tel: 27 012 352 4278
Fax: 27 012 352 4270
E-mail: joubeed@unisa.ac.za
Balakrishna Pillay
Department of Microbiology
Westville Campus
University of KwaZulu-Natal
Private Bag X 54001
Durban, 4000
South Africa
Tel: 27 031 260 7404
Fax: 27 031 260 7809
E-mail: pillayb1@ukzn.ac.za
*Corresponding
author
Keywords: biofilm,
microbial biodiversity, schmutzdecke.
Abbreviations: |
ESEM: environmental scanning electron
microscopy
SEM: scanning electron microscopy
SSF: slow sand filtration |
The removal of contaminants in slow sand filters
occurs mainly in the colmation layer or schmutzdecke - a biologically active
layer consisting of algae, bacteria, diatoms and zooplankton. A ripening period
of 6 - 8 weeks is required for this layer to form, during which time filter
performance is sub-optimal. In the current study, an environmental scanning
electron microscope was used to visualise the ripening process of a pilot-scale
slow sand filter over a period of eight weeks. To achieve this, sand particles
were removed at weekly intervals and observed for biofilm development. Biological
mechanisms of removal in slow sand filtration are not fully understood. A
visualisation of the colonisation process would enhance the knowledge and
understanding of these mechanisms. Colonisation of sand particles and increase
in biomass was clearly seen during the ripening period. The mature, ripened
filter exhibited a dense extracellular matrix consisting of a wide variety of
microorganisms and their extracellular and breakdown products. This research
demonstrated the successful use of an environmental scanning electron
microscope to visualise the complex, heterogeneous nature of the schmutzdecke
in a slow sand filter. Such knowledge could possibly lead to an increase in the
application of slow sand filtration, especially for rural communities.
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