An Assessment of Winery Wastewater Diluted for Irrigation of Grapevines in the Breede River Valley with Respect to Water Quality and Nutrient Load

Abstract

Possible re-use of winery wastewater for irrigation was investigated in a field trial with micro-sprinklerirrigated Cabernet Sauvignon/99 Richter in the Breede River Valley region of South Africa. Irrigation with winery wastewater diluted to 100, 250, 500, 1 000, 1 500, 2 000, 2 500 and 3 000 mg/L chemical oxygen demand (COD), respectively, was compared to irrigation with raw river water. Since the pH was lower than 6, the diluted wastewater could cause nutrient toxicity. The diluted winery wastewater did not pose any salinity hazard, as the electrical conductivity was well below 2 dS/m. For the given range of dilutions, the sodium adsorption ratio never exceeded 10, which indicates that the water posed no sodicity hazard. Sodium and Cl- never exceeded 115 and 150 mg/L, the respective upper thresholds for grapevines. With the exception of N, levels of H2PO4 -, K+, Na+, Ca2+, Mg2+, HCO3 -, SO4 2- and B3+ in the diluted wastewater increased with a decrease in dilution level. The N load in diluted winery wastewater appeared to be completely inadequate to supply the grapevine’s requirements. In contrast, the P load in the winery wastewater diluted to 2 500 mg/L COD and higher would supply more than adequate P if the grape yield amounts to 10 t/ha. Likewise, the dilution of winery wastewater to 250 mg/L COD and higher would supply more than adequate K+ if the grape yield amounts to 10 t/ha. However, K+ applied via the wastewater will only be beneficial if it is not leached from the root zone during winter.