136
E.M. Nupen and G.J. Stander
At the start of plant operation for the 1970-1971 season the water shortage was very
critical and it seemed doubtful if the new von Bach Dam water would be available in
time; indeed, in February 1971 the Goreangab Dam source was exhausted and for one
week the city had to rely on reclaimed water and borehole water only. In view of the
anticipated new supplies and doubt as to the origin of the virus isolated at the end of the
previous season in the mixed water, it was decided at the beginning of the 1970-1971
season that, during this period of plant operation, not only reclaimed water but all
sources of water supplied to the city should routinely be monitored weekly for virus.
Bacteriological tests were made on all samples tested for virus, including confirmed E.
coli I, total plate counts and salmonella evaluations. At no time during the 1970-71
season which ended in February 1971 was virus isolated in the plant after the break-point
chlorination stage or in the finally reclaimed water or in 10 litres of the mixed
conventionally purified Goreangab Dam water and reclaimed water.
During February 1971 Windhoek had unprecedented heavy rains which relieved the
water shortage, overflowing the Goreangab Dam and filling the Avis Dam. At the end of
February also the von Bach Dam was completed and became an additional source of
supply. By this time the Gammams Sewage Works had become overloaded and was
producing an effluent which was unsuitable for treatment in the maturation ponds. In
view of the now abundant water supply it was therefore decided to discontinue waste
water reclamation for the rest of the season while alterations to the sewage works were
undertaken and also to allow for the re-stabilization of the maturation ponds. Testing of
other sources of water supply continued so as to enable correlations to be made with the
epidemiological studies.
Virus Testing of Sources of Supply other than Reclaimed Water
Weekly monitoring was done on raw Goreangab Dam water, raw Avis Dam water,
purified von Bach Dam water, purified Goreangab Dam water, purified Avis Dam water
and water from the distribution system.
No virus was isolated in purified von Bach Dam, purified Avis Dam water or from the
distribution system. However, in raw Goreangab Dam water enterovirus was isolated on
22nd March 1971, reovirus was isolated on 27th April 1971 p>632 TCID 50 /10 1) and
again on 19th July 1971. Enterovirus was isolated from raw Avis Dam water on 14th
June 1971. Reovirus was isolated from conventionally purified Goreangab Dam water on
1st June 1971 and enterovirus on 14th June 1971. Again this water received a further
chlorine dosage at the central reservoir before entering the reticulation system.
From the above findings it is apparent that virus can be present in supposedly clean
natural raw water supplies and no absolute reliance can be placed on natural purification
processes. It can be seen from the isolation of virus after conventional purification of
these waters that it is of the utmost importance that conventional purification processes
be such that virus can be fully inactivated by properly controlled treatment procedures,
especially as far as pH, turbidity and chlorination are concerned.
Chlorination Problem and Viruses
Clarke (1964), Chang (1968), Weidenkopf (1958), Kelly and Sanderson (1958, 1960)
have all shown that HOC1 is considerably more effective than the OCl~ ion in the
inactivation of virus. It is greatly more effective than ammonia chloramines or organic
chloramines (Clarke and Chang 1959; and Kjellander and Lund 1965). The enteric viruses
appear to differ in their resistance to free chlorine (Clarke et al 1964).
E.M. Nupen and G.J. Stander
At the start of plant operation for the 1970-1971 season the water shortage was very
critical and it seemed doubtful if the new von Bach Dam water would be available in
time; indeed, in February 1971 the Goreangab Dam source was exhausted and for one
week the city had to rely on reclaimed water and borehole water only. In view of the
anticipated new supplies and doubt as to the origin of the virus isolated at the end of the
previous season in the mixed water, it was decided at the beginning of the 1970-1971
season that, during this period of plant operation, not only reclaimed water but all
sources of water supplied to the city should routinely be monitored weekly for virus.
Bacteriological tests were made on all samples tested for virus, including confirmed E.
coli I, total plate counts and salmonella evaluations. At no time during the 1970-71
season which ended in February 1971 was virus isolated in the plant after the break-point
chlorination stage or in the finally reclaimed water or in 10 litres of the mixed
conventionally purified Goreangab Dam water and reclaimed water.
During February 1971 Windhoek had unprecedented heavy rains which relieved the
water shortage, overflowing the Goreangab Dam and filling the Avis Dam. At the end of
February also the von Bach Dam was completed and became an additional source of
supply. By this time the Gammams Sewage Works had become overloaded and was
producing an effluent which was unsuitable for treatment in the maturation ponds. In
view of the now abundant water supply it was therefore decided to discontinue waste
water reclamation for the rest of the season while alterations to the sewage works were
undertaken and also to allow for the re-stabilization of the maturation ponds. Testing of
other sources of water supply continued so as to enable correlations to be made with the
epidemiological studies.
Virus Testing of Sources of Supply other than Reclaimed Water
Weekly monitoring was done on raw Goreangab Dam water, raw Avis Dam water,
purified von Bach Dam water, purified Goreangab Dam water, purified Avis Dam water
and water from the distribution system.
No virus was isolated in purified von Bach Dam, purified Avis Dam water or from the
distribution system. However, in raw Goreangab Dam water enterovirus was isolated on
22nd March 1971, reovirus was isolated on 27th April 1971 p>632 TCID 50 /10 1) and
again on 19th July 1971. Enterovirus was isolated from raw Avis Dam water on 14th
June 1971. Reovirus was isolated from conventionally purified Goreangab Dam water on
1st June 1971 and enterovirus on 14th June 1971. Again this water received a further
chlorine dosage at the central reservoir before entering the reticulation system.
From the above findings it is apparent that virus can be present in supposedly clean
natural raw water supplies and no absolute reliance can be placed on natural purification
processes. It can be seen from the isolation of virus after conventional purification of
these waters that it is of the utmost importance that conventional purification processes
be such that virus can be fully inactivated by properly controlled treatment procedures,
especially as far as pH, turbidity and chlorination are concerned.
Chlorination Problem and Viruses
Clarke (1964), Chang (1968), Weidenkopf (1958), Kelly and Sanderson (1958, 1960)
have all shown that HOC1 is considerably more effective than the OCl~ ion in the
inactivation of virus. It is greatly more effective than ammonia chloramines or organic
chloramines (Clarke and Chang 1959; and Kjellander and Lund 1965). The enteric viruses
appear to differ in their resistance to free chlorine (Clarke et al 1964).