South Africa Wine Technical Yearbook 2025

FIGURE 3. Temporal variation in (A) HCO 3 2- , (B) Cl - and P, (C) pH and (D) chemical oxygen demand (COD) in wastewater from a winery near Rawsonville. Shaded columns indicate the harvest periods. Dashed lines indicate Cl - , pH and COD thresholds. - and SO 4

Rainfall and volumes of wastewater applied Mean monthly rainfall was typical for a Mediterranean climate (Figure 4). However, the July rainfall was abnormally low in all the winters compared to the long-term average for Rawsonville (data not shown). Winter rainfall, i.e. from April to September, amounted to 380 mm, 420 mm and 685 mm in 2011, 2012 and 2013, respectively. During the harvest period from February until April, WWW irrigation amounts were substantially higher (Figure 5). During the peak period, in March, ca . 23 mm irrigation was applied per day. In December, the soil received only ca . 3 mm wastewater per day. The irrigation volumes also increased from mid-winter to reach a second peak in August when bottling occurred. Total irrigation applied from April to September, amounted to 1 475 mm, 2 600 mm and 3 285 mm in 2011, 2012 and 2013, respectively. Based on the foregoing, the soil received the

highest irrigation plus rainfall in the winter of 2013, followed by 2012 and then 2011. The application of WWW resulted in die-back of the grass on the irrigated area after only one month (Figure 6A). This could have been the result of oxygen depletion in the topsoil due to the high level of COD in the WWW. Most wineries that applied their WWW through land application do not measure how much wastewater they are applying, and their strategy is to irrigate an area until the plants die off and then move the sprinkler. The plants normally recover after three months. The soil also became totally waterlogged and the WWW ponded on the soil after irrigation was applied, particularly in winter. Due to the waterlogging, part of the water-soluble organic fraction of the WWW accumulated in the topsoil and in the ponded water on the soil (Figure 6B). The organic matter probably underwent anaerobic

FIGURE 4. Mean monthly rainfall during the study period at a winery near Rawsonville.

FIGURE 5. Mean monthly wastewater applied during the study period at a winery near Rawsonville.

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TECHNICAL YEARBOOK 2025