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Table L7:
269
Some South African industrial water consumption data including wastewater quality information (continued).
Industry Details
Tanning and leather Twenty tanneries are found in South Africa, which together process approximately 2 x 10 6 hides"every year.
finishing Industry Annual water consumption is some 600 000 m 3 , nearly all of which is discharged as wastewater. A mean full
tanning SWI of 432 t per hide (within the range 320 - 744 t per hide) was found. A target SWI of 430 t per
hide was proposed. The SPL varied between 0,9 - 6,8 kg COD per hide (mean of 3,7 kg COD per hide); 2,6 -
8,9 kg total dissolved solids per hide (mean of 7,7 kg total dissolved solids per hide): 0,5 - 1,4 kg suspended
solids per hide (mean of 0,8 kg suspended solids per hide), and 0,01 - 0,2 kg chromium per hide (mean of 0,1 kg
chromium per hide). A target SPL of 1,0 kg COD per hide, 3,0 kg total dissolved solids per hide, 0,5 kg
suspended solids per hide, and less than 0,01 kg chromium per hide, has been proposed. Problems are evident
with the economic purification of wastewater from tanneries, where the technology for treatment to effluent
standards is not available
Sugar industry There are 16 sugar cane processing plants and one refinery In South Africa, which together produce
approximately 12,0 x 10 6 t of sugar per annum (1985 data). Of the 16 processing plants, 10 are mills only, and
six are mills with an attached '"back-end" refinery (the latter situation is assuming increased importance in the
sugar industry). Sugar cane consists largely of water (70% by mass), where the industrial process involves
extracting sugar crystals from a solution. Accordingly, most of the water in the sugar cane as well as the plant
water intake is evaporated and can be recovered as condensate. The SWI varied from 30 - 100 m 3 per 100
tonnes of sugar cane processed, with a mean SWI of 60 m 3 per 100 tonnes of cane processed. Wastewater
volumes (given the nature of the manufacturing technique) are fairly small (some 30% of the water Intake), or
approximately 750 - 1 500 m 3 on a daily basis. The COD of wastewater generally varies between 1 500-
2000 mg t-' (due mainly to sugar lost in washing, and as a result of cooling-water overflows). Problems are
evident with sugar plant wastewaters, since the COD load is almost totally soluble, leading to sludge bulking and
sludge loss problems in conventional biological treatment works. Solid wastes include boiler ash and smuts
which are disposed of as landfill, as well as filter cake from the milling process which can be used as fertilizer