134
E.M. Nupen and G.J. Stander
molecular weight of R.N.A.
It was found that virus could be recovered from the cell membrane by flooding the
membrane with Hacks' balanced salt solution (HBSS), with the addition of 10 per cent
foetal calf serum and 0.5 per cent lactalbumin hydrolysate. A total of 20 ml concentrate
was treated with 3 ml chloroform for 18 hr, centrifuged at 2000 rev min"
1 for 30 min and
the supernatant used for evaluation by the roller-tube method to determine the 50 per
cent tissue culture infective dose (TCID 50 ) or by plaquing to determine the plaque
forming unit (P.F.U.) count.
This method has given an average of 70 per cent recovery of virus and has the
advantage of allowing 10 litres or more of clear water or even slightly turbid samples to
be processed in a matter of hours. The membrane is however extremely delicate and care
must be taken to ensure that no damage occurs before or during filtration.
Bacteriological Methods
Membrane filtration with incubation of the membrane^ pn MacConkey membrane agar
at 40.0°C for 24 hr was used for Eschericha coli I counts \vith confirmation by testing for
in dole production. Yeast extract agar with incubation at 22°C was used for total plate
counts. Salmonella evaluation methods used were as described by Grabow et al (in
preparation).
RESULTS
Waste Water Reclamation Plant Monitoring
The design and working of the Windhoek Waste Water Reclamation Plant has been
fully described (Cillie et al 1966; Stander and van Vuuren 1969; van Vuuren et al 1965,
1967, 1968, 1970), but the following points should be re-stressed. The plant was designed
to meet certain needs. Firstly Windhoek was heading for a serious water shortage and the
time factor was important;. Windhoek at the start of waste water reclamation had only
two sources of supply, which were conventionally purified water from the Goreangab
Dam containing only 20 per cent of its capacity, and water from boreholes showing
evidence of a decreasing supply. The new dam S. von Bach was in the process of
construction but was not expected to be completed until February 1971, and the Avis
Dam was completely empty. Readily available, for reclamation purposes, was a water
source from the series of nine maturation ponds which further purified the
conventionally treated sewage from the Gammams Sewage Purification Works to a higher
quality effluent. This effluent is lower in ammonia concentration during the summer
months due to more effective algal action in the ponds. Reclamation plant design was
such that the algae could be effectively removed by the floatation process. Although virus
is removed by floatation, settling, sand filtration and carbon filtration to a high degree,
final assurance for complete inactivation of virus must always be on disinfection; it is
therefore essential to ensure break-point chlorination at all times. The chlorination
facilities installed, which were governed by cost limitations (van Vuuren et al 1970), were
such that effective break-point chlorination with a resultant safe free chlorine residual
could only be accomplished during the summer months when the ammonia concentration
of the maturation ponds was at a low pre-determined level. During the winter months the
reclamation plant is shut down due to this cost factor. Nevertheless the water reclaimed
during the summer months considerably relieved the strain on the already depleted
E.M. Nupen and G.J. Stander
molecular weight of R.N.A.
It was found that virus could be recovered from the cell membrane by flooding the
membrane with Hacks' balanced salt solution (HBSS), with the addition of 10 per cent
foetal calf serum and 0.5 per cent lactalbumin hydrolysate. A total of 20 ml concentrate
was treated with 3 ml chloroform for 18 hr, centrifuged at 2000 rev min"
1 for 30 min and
the supernatant used for evaluation by the roller-tube method to determine the 50 per
cent tissue culture infective dose (TCID 50 ) or by plaquing to determine the plaque
forming unit (P.F.U.) count.
This method has given an average of 70 per cent recovery of virus and has the
advantage of allowing 10 litres or more of clear water or even slightly turbid samples to
be processed in a matter of hours. The membrane is however extremely delicate and care
must be taken to ensure that no damage occurs before or during filtration.
Bacteriological Methods
Membrane filtration with incubation of the membrane^ pn MacConkey membrane agar
at 40.0°C for 24 hr was used for Eschericha coli I counts \vith confirmation by testing for
in dole production. Yeast extract agar with incubation at 22°C was used for total plate
counts. Salmonella evaluation methods used were as described by Grabow et al (in
preparation).
RESULTS
Waste Water Reclamation Plant Monitoring
The design and working of the Windhoek Waste Water Reclamation Plant has been
fully described (Cillie et al 1966; Stander and van Vuuren 1969; van Vuuren et al 1965,
1967, 1968, 1970), but the following points should be re-stressed. The plant was designed
to meet certain needs. Firstly Windhoek was heading for a serious water shortage and the
time factor was important;. Windhoek at the start of waste water reclamation had only
two sources of supply, which were conventionally purified water from the Goreangab
Dam containing only 20 per cent of its capacity, and water from boreholes showing
evidence of a decreasing supply. The new dam S. von Bach was in the process of
construction but was not expected to be completed until February 1971, and the Avis
Dam was completely empty. Readily available, for reclamation purposes, was a water
source from the series of nine maturation ponds which further purified the
conventionally treated sewage from the Gammams Sewage Purification Works to a higher
quality effluent. This effluent is lower in ammonia concentration during the summer
months due to more effective algal action in the ponds. Reclamation plant design was
such that the algae could be effectively removed by the floatation process. Although virus
is removed by floatation, settling, sand filtration and carbon filtration to a high degree,
final assurance for complete inactivation of virus must always be on disinfection; it is
therefore essential to ensure break-point chlorination at all times. The chlorination
facilities installed, which were governed by cost limitations (van Vuuren et al 1970), were
such that effective break-point chlorination with a resultant safe free chlorine residual
could only be accomplished during the summer months when the ammonia concentration
of the maturation ponds was at a low pre-determined level. During the winter months the
reclamation plant is shut down due to this cost factor. Nevertheless the water reclaimed
during the summer months considerably relieved the strain on the already depleted