Abstract:
This study compared three Escherichia coli (E. coli) detection methods to
determine an optimum method to use in assessing the health-related
microbiological water quality in surface water of the Middle Modder River
catchment. As an outcome, the study recommends an optimum method for two
types (varying pollution status) of river water.
Faecal coliforms and E. coli were selected as microbiological indicator organisms.
The three methods were based on colour changes to indicate the presence of the
selected organism groups. Two of the methods were membrane-filtration based
while the other was based on the Most Probable Number technique. The
membrane-based methods used the reagent media M-FC (for faecal coliforms) and
Chromocult Coliform® Agar for E. coli respectively. These were compared with the
miniaturised liquid-based Most Probable Number (MPN) using the Quanti-Tray® I
2000 -Colilert 18 method for E. coli.
The Colilert method turned out to be the optimum method for the water selected for
this study. Higher numbers of true indicator organisms were detected by this
method than by the other two methods in all the selected waters.
Using the identified optimum method, the following was determined:
o The E. coli numbers in the water of the Modder River (at the 90th percentile
compliance limit) exceeded recommended water quality guideline limits
(South African Water Quality Guidelines, the Quality of Domestic Water
Supplies: Assessment Guide as well as the National Microbial Monitoring
Programme) for indicator organisms in water for domestic use (drinking, food preparation, bathing and laundry) and recreation waters.
The E. coli numbers did not exceed recommended water quality guideline
limits for indicator organisms where the intended use was for crop irrigation.
Water in the Modder River was suitable for raw water extraction to treat for
use as drinking water.
Abstract
