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South African
Wine Lab Association:

Effect of Irrigation with Diluted Winery Wastewater on Phosphorus in Four Differently Textured Soils

A.R. Mulidzi1*, C.E. Clarke2, P.A. Myburgh1

The wine industry needs solutions for wastewater treatment, as environmental legislation for its disposal is
increasingly being enforced due to non-compliance. The feasibility of re-using diluted winery wastewater
was assessed in a pot experiment under a rain shelter over four simulated irrigation seasons. Four soils
varying in parent material and clay content, viz. aeolic sand from Lutzville containing 0.4% clay, alluvial
sand from Rawsonville containing 3.3% clay, granite-derived soil from Stellenbosch containing 13% clay,
and shale-derived soil from Stellenbosch containing 20% clay, were irrigated with wastewater diluted to
3 000 mg/L COD (chemical oxygen demand), whereas the control received municipal water. Irrigation with
diluted winery wastewater increased the pH(KCl) in the shale- and granite-derived soils into the optimum
range for P availability. Although pH(KCl) in the aeolic sand was initially above the optimum range, relatively
high Na+ levels also caused available P to increase as the pH(KCl) increased. The pH(KCl) in the alluvial sand
increased beyond the optimum range, thereby causing a reduction in the available P. This indicates that
irrigation with diluted winery wastewater may only enhance P absorption if the pH(KCl) shift is towards the
optimum. It must be noted that the results represent a worst-case scenario, i.e. in the absence of rainfall
or crops.

Chemical oxygen demand, pot experiment, solubility, soil pH, water quality

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