Water Science & Technology: Water Supply Vol 1 No 1 pp 97–06 © IWA Publishing 2001
Occurrence and removal of Giardia and Cryptosporidium
at the Goreangab reclamation plant
JG Menge*, J Haarhoff**, E König***, R Mertens**** and B van der Merwe*****
*
Department Infrastructure, Water & Technical Services, PO Box 59, Windhoek,
Namibia
**
Department of Civil Engineering, Rand Afrikaans University, PO Box 524,
Auckland Park, 2006 South Africa
***
Department Infrastructure, Water & Technical Services, PO Box 59, Windhoek,
Namibia
****
Department Infrastructure, Water & Technical Services, PO Box 59, Windhoek,
Namibia
*****
Enves, PO Box 6373, Ausspannplatz, Windhoek, Namibia
ABSTRACT
This paper deals with the occurrence of Giardia and Cryptosporidium in the
water sources available for the Goreangab Reclamation Plant (GRP) and the
subsequent removal during treatment at the reclamation plant. Giardia is
detected more often than Cryptosporidium. 60% of the time it is detected
in the samples from the dam and in 55% of the samples from the maturation
pond effluent.
During the investigation, Giardia was detected in the final water 5% of the
time and Cryptosporidium 2% of the time. The maximum Giardia cysts detected
in a sample was 30, the 99% percentile was 20 and the 97% percentile 10
cysts. A maximum of 20 Cryptosporidium oocysts was detected in a sample.
The 99% percentile counted 6.2 oocysts and the 97% percentile 0 oocysts.
From the data presented it is clear that the polluted dam water has the
same risk level of Giardia and Cryptosporidium pollution as treated
wastewater effluent. This emphasises the fact that the sources should
be monitored continuously for these parasites. The sporadic high counts
of Giardia and Cryptosporidium in the raw water sources indicate that a
multiple-barrier approach must be followed to ensure the safe operation
of even conventional treatment plants using polluted source water.
No correlation could be found between cyst and oocyst removal and other
water quality parameters.
The advocating of a final water turbidity of 0.1 NTU and the use of
particle counters can only be supported by these findings, as it is
possible to achieve a turbidity of less than 0.1 NTU at the sand filter
outlet, even in a developing country like Namibia. The challenge lies
with the maintenance of equipment and vigilance of the operators.
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