Abstract:
NATREF is the only inland refinery in South Africa and as such has unique
water disposal challenges since it does not have the advantage of marine outlet
like many other refineries. Most of its process streams are treated by the Sasol
water treatment facility, leaving the concern of water that collects and drains off
during rain fall events from the refinery site. Two sampling points were used
during this study. Temperature and pH were measured in situ while bacterial
counts and algal bioassays were performed in VUT laboratory. The area
experienced a total of 485 mm of rain during the study period with 75 % thereof
during spring and summer, there rest in autumn and winter receiving no rain.
The average seasonal pH of the samples remained between 8 and 9.3 and this
was found to fall within TWQR as well as being within normal range for natural
waters. The temperature changes followed a typical summer/winter pattern, with
Taaibosch Spruit showing greater variations from 10.95 ˚C in winter to 21.4 ˚C in
summer due to its shallow nature. TDS, Nitrates & phosphates were all above
the TWQR. Higher HPC & FC counts were observed during spring when rain
storms began with Taaibosch Spruit had the higher of the two. As the rainfall
continued into summer, the most of the bacterial counts decreased up to the
lowest in winter. Higher than expected coliform counts (between 0 and 8 x 104)
were observed, indicating a possible source of pollution which has to be studied.
Chlorophyll a values ranged from 2.85 μg/L during spring to100 μg/L in winter
indicating the potential for stimulation of the algae and possible algal blooms.
The algal bioassays showed inhibition potential of the water during spring,
summer and autumn with recovery by the winter. This meant that the storm
water from NATREF does have a potential to cause chemical & biological
pollution of the Taaibosch Spruit although the actual source of storm water
pollution has to be properly studied.
