RESEARCH IN ACTION

 

Functional characterization of heterotrophic denitrifying bacteria in activated sludge

 

 

Nishani Ramdhani; Faizal Bux

Centre for Water and Wastewater Technology, Department of Biotechnology, Durban University of Technology, P.O. Box 1334, Durban 4000, South Africa

 

 

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ABSTRACT

Wastewater treatment facilities are largely accountable for the detrimental enrichment of water bodies with nitrogenous compounds, resulting in eutrophication. Denitrification is of interest as a means of removing nitrates and nitrites from water supplies because they are also hazardous to human health. The integration of biological nutrient removal into conventional wastewater treatment processes has, however, failed to take into sufficient consideration the role of key microorganisms present, specifically denitrifying bacteria. The purpose of the study reported here was to group such heterotrophic denitrifying bacteria using a series of biochemical and molecular analyses, to achieve an improved understanding of their functions. The role of the denitrifying bacteria in reducing nitrate and nitrite was monitored using the colorimetric nitrate reduction test. The genetic diversity of the culture collection was investigated by the use of denaturing gradient gel electrophoresis (DGGE), which enabled the creation of a microbial population profile of eight predominant isolates. Batch experiments were conducted on these isolates, the results of which ultimately confirmed their classification according to their respective functions, namely, incomplete denitrifiers, true denitrifiers, sequential denitrifiers, and exclusive nitrite reducers.

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* Author for correspondence. E-mail: nishani@dut.ac.za