Handbook for Irrigation of Wine Grapes in South Africa

Chapter 5

TABLE 5.12. The effect of irrigation with treated municipal wastewater on the cane mass and yield of two grapevine cultivars, compared to no irrigation (dryland) near Philadelphia. Cane mass and yield data are means for four and five years, respectively. Cultivar Cane mass (t/ha) Yield (t/ha) Dryland Irrigated Dryland Irrigated Sauvignon blanc 0.6±0.3 1.6±0.7 6.9±4.4 11.2±3.8 Cabernet Sauvignon 1.1±0.8 2.1±0.6 6.6±3.6 12.3±2.7 WINERY WASTEWATER Wine production is an important industry in the Western Cape and the Lower Orange region in the Northern Cape. Wineries inevitably produce large volumes of low quality wastewater, particularly during the harvest period. International requirements, as well as national legislation, are putting pressure on wine producers regarding the responsible management of winery wastewater, which may have a large-scale detrimental impact on the environment. The wine industry has co-funded various projects in the past in an effort to develop technology that will contribute to responsible management of distillery and winery wastewater. Reducing the problem has already initiated technological innovation with regard to winery wastewater treatment. The latter is not necessarily a sustainable solution, as wastewater treatment may result in high energy use and emission of greenhouse gasses, contributing to global warming. Furthermore, constantly increasing electricity costs will be a challenge to the economic viability for high energy- demanding processes required for wastewater treatment. In many cases, wineries will only (i) remove coarse particles such as stems and pips by screening, (ii) adjust the pH and (iii) allow sedimentation before it is sprayed onto grazing paddocks (Fig. 5.15). Sometimes, additional wastewater treatment such as aeration is also carried out in order to reduce the excessively high COD concentrations. Vanes driven by electric motors mounted on floats can be used for mechanical aeration to reduce the level of COD (Fig. 5.16). Aeration can reduce the COD in a fairly large body of wastewater below the highest permissible level throughout the year (Fig. 5.17). During the annual harvesting and crushing peaks, i.e. when vineyards still need irrigation, the permissible volume of wastewater per day is extremely limited (Table 5.11). Consequently, it does not allow much scope for irrigation of large areas under grapevines. If the water could be stored in large enough dams, it could be used for irrigation of larger areas during the first part of the following season. However, finding suitable dam sites near wineries might be difficult. Furthermore, initial capital layout and high energy requirements will make large scale aeration and storage a costly practice. 5.6.2

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