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E.M. Nupen and GJ. Stander
CONCLUSIONS
On routine monitoring no virus was isolated from the final effluent of the Windhoek
Waste Water Reclamation Plant. Virus was isolated from the mixed conventionally
purified Goreangab Dam and reclaimed waters. Intensive testing of all other sources of
water supply to the Windhoek area resulted in the isolation of virus from raw natural
water supplies and also from conventionally purified Goreangab Dam water.
On epidemiological evidence the absence of E. coli I in 100 ml of drinking water has
been a reasonably dependable indicator of the bacteriological safety of drinking water,
although it is fully realised that this standard does not guarantee the absence of
pathogenic organisms from 100 ml or even more of the same water. It is impracticable to
routinely monitor enormous quantities of water for the possible presence of all viruses. In
the light of the findings of present concentration techniques, the absence of enterovirus
in ten litres of sample should give the necessary confidence that a water is of a
permissibly safe quality for drinking purposes. Indeed, it may be asked how many
conventionally purified drinking water supplies can meet such a standard?
The importance of properly controlled break-point chlorination with consideration of
pH and turbidity is of cardinal importance not only in the disinfection of reclaimed water
but in all treated waters destined for drinking purposes.
In the monitoring of the reclamation plant and in all investigations on the Windhoek
water supplies, the presence of entero- or reoviruses only has been evaluated. Immediately
the question arises with regard to the infectious hepatitis virus. In spite of the fact that no
known methods exist to date for the detection of this virus in vitro, findings have shown
firstly that this virus is inactivated by efficient break-point chlorination (Neefe et al
1947) and secondly, that the virus has not been implicated in epidemics due to drinking
water where the water has received complete conventional water treatment with
break-point chlorination disinfection (Report on Hepatitis 1965).
In conformity to European Standards for Drinking Water WHO (1970), the resistant
enterovirus is used as an indication of viral pollution and for reasons quoted there it is not
necessary or feasible to test for all possible viruses.
For the purpose of supplying safe drinking water to a community, it is axiomatic to
accept that all raw water supplies, even underground water, not only in South Africa, but
in virtually every country in the world can be contaminated with virus. The days of
protected catchments and impoundments are over, and the treatment in a conventional
plant of what is virtually wastewater for drinking purposes is already world wide practice.
The one major difference between this practice and the direct reclamation of wastewater
is that in a tertiary system the process units are designed in accordance with
environmental factors and the variables are under proper chemical and engineering
control. This control is not always possible in the conventional purification of polluted
waters where variations in self-purification and dilution are increasingly changing.
This project at Windhoek has taught us a number of important lessons.
1. While involved with the reclamation of sewage we were obviously forced to look
critically into health aspects and, in time, it became obvious that we had also to look
at conventional water purification facilities with the same degree of criticism.
2. Conventional water purification procedures, as they exist today in thousands of water
supplies, are just not adequate to ensure safe drinking water because of polluted water
intake.
3. When dealing with the treatment of polluted waters, whether these be sewage
E.M. Nupen and GJ. Stander
CONCLUSIONS
On routine monitoring no virus was isolated from the final effluent of the Windhoek
Waste Water Reclamation Plant. Virus was isolated from the mixed conventionally
purified Goreangab Dam and reclaimed waters. Intensive testing of all other sources of
water supply to the Windhoek area resulted in the isolation of virus from raw natural
water supplies and also from conventionally purified Goreangab Dam water.
On epidemiological evidence the absence of E. coli I in 100 ml of drinking water has
been a reasonably dependable indicator of the bacteriological safety of drinking water,
although it is fully realised that this standard does not guarantee the absence of
pathogenic organisms from 100 ml or even more of the same water. It is impracticable to
routinely monitor enormous quantities of water for the possible presence of all viruses. In
the light of the findings of present concentration techniques, the absence of enterovirus
in ten litres of sample should give the necessary confidence that a water is of a
permissibly safe quality for drinking purposes. Indeed, it may be asked how many
conventionally purified drinking water supplies can meet such a standard?
The importance of properly controlled break-point chlorination with consideration of
pH and turbidity is of cardinal importance not only in the disinfection of reclaimed water
but in all treated waters destined for drinking purposes.
In the monitoring of the reclamation plant and in all investigations on the Windhoek
water supplies, the presence of entero- or reoviruses only has been evaluated. Immediately
the question arises with regard to the infectious hepatitis virus. In spite of the fact that no
known methods exist to date for the detection of this virus in vitro, findings have shown
firstly that this virus is inactivated by efficient break-point chlorination (Neefe et al
1947) and secondly, that the virus has not been implicated in epidemics due to drinking
water where the water has received complete conventional water treatment with
break-point chlorination disinfection (Report on Hepatitis 1965).
In conformity to European Standards for Drinking Water WHO (1970), the resistant
enterovirus is used as an indication of viral pollution and for reasons quoted there it is not
necessary or feasible to test for all possible viruses.
For the purpose of supplying safe drinking water to a community, it is axiomatic to
accept that all raw water supplies, even underground water, not only in South Africa, but
in virtually every country in the world can be contaminated with virus. The days of
protected catchments and impoundments are over, and the treatment in a conventional
plant of what is virtually wastewater for drinking purposes is already world wide practice.
The one major difference between this practice and the direct reclamation of wastewater
is that in a tertiary system the process units are designed in accordance with
environmental factors and the variables are under proper chemical and engineering
control. This control is not always possible in the conventional purification of polluted
waters where variations in self-purification and dilution are increasingly changing.
This project at Windhoek has taught us a number of important lessons.
1. While involved with the reclamation of sewage we were obviously forced to look
critically into health aspects and, in time, it became obvious that we had also to look
at conventional water purification facilities with the same degree of criticism.
2. Conventional water purification procedures, as they exist today in thousands of water
supplies, are just not adequate to ensure safe drinking water because of polluted water
intake.
3. When dealing with the treatment of polluted waters, whether these be sewage