Handbook for Irrigation of Wine Grapes in South Africa

10 000 12 000 14 000 16 000

0 2 000 4 000 6 000 8 000 C2D (mg  )

FIGURE 5.17. Seasonal variation in COD in aerated winery wastewater after aeration commenced in January 2006 (data supplied by the courtesy of the Botha winery). Brackets indicate annual harvesting and crushing peaks. Dashed lines are the permissible COD levels, depending on the volume irrigated per day as indicated in Table 5.11. 15-Jan-06 15-May-06 15-Sep-06 15-Jan-07 15-May-07 15-Sep-07 15-Jan-08 15-May-08 Figure 5.18 In most wine producing regions, vineyards need irrigation. Therefore, the ideal situation would be to implement sustainable re-use of winery wastewater for irrigation by adding it to existing irrigation water resources. The dilution of winery wastewater could become a necessity in the future, as water shortages and/or costs escalate. However, knowledge on the impact of irrigation with diluted winery wastewater on soil chemical and physical properties, as well as grapevine performance and wine quality, is limited. An important aspect is that the General Authorization for using winery wastewater first needs to be adapted by the Department of Water and Sanitation to legalize the use of diluted winery wastewater. However, before any changes can be made to the General Authorization there must be scientifically based proof for the sustainability of using diluted winery wastewater for crop irrigation. As part of the process to motivate for changing the General Authorization for wineries, the possibility of using diluted winery wastewater for vineyard irrigation was investigated in a field trial near Rawsonville in the Breede River Valley (Myburgh & Howell, 2014b). Wastewater obtained from a co-operative winery was diluted with fresh river water to COD levels of 100, 250, 500, 1 000, 1 500, 2 000, 2 500 and 3 000 mg/  , respectively (Myburgh et al. , 2015). Irrigation with only river water served as the control. The irrigation treatments were applied to Cabernet Sauvignon grapevines planted in a sandy, alluvial soil. Parallel to the field trial, effects of diluted winery wastewater on the chemical properties of different soils were studied in a pot trial under a rain shelter at Stellenbosch. Four soils, i.e. (i) alluvial sand from Rawsonville, (ii) aeolic sand from Lutzville, (iii) shale-derived soil from Stellenbosch and (iv) granite-derived soil from Stellenbosch, were irrigated with wastewater diluted to 3 000 mg/  COD (Mulidzi et al. , 2015a). In a follow-up study, the four soils, plus a sandy loam soil from Robertson and a duplex soil from Stellenbosch, were first irrigated with 3 000 mg/  COD winery wastewater, and then

130 CHAPTER 5 – IRRIGATION WATER QUALITY