Microbial Biotechnology


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

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.


ESEM: environmental scanning electron microscopy
SEM: scanning electron microscopy
SSF: slow sand filtration

Abstract   Full Text

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.

Supported by UNESCO / MIRCEN network