Technical Yearbook 2024

SEPTEMBER

In-field fractional use of winery wastewater with raw water (Part 2): Irrigation application, water quality and nutrient load By Carolyn Howell & Reckson Mulidzi Abstract Wineries produce large volumes of poor quality

Introduction Winery wastewater contains high levels of potassium (K) and sodium (Na) which originate from cleaning products, grape lees and spillage from the grape fermentation process. 1,2,3,4,5,6 The levels of these two ions are largely dependent upon the nature of the cleaning agents used in a particular winery. 7 High K levels are common in winery wastewater, because of the high concentrations of K in grape juice. Winery wastewater can also contain low levels of calcium (Ca) and magnesium (Mg). 3,7 Neither of these are harmful to soil structure and could help to ameliorate the impact of Na in the wastewater by reducing the sodium adsorption ratio (SAR). 7 The organic material in winery wastewater is generated from the grapes and wine. 3 Different winemaking processes can affect the composition of winery wastewater. 8 In the case of off-skin winemaking, sugars are the main component of the organic load in the effluent water, whereas classical winemaking methods generate wastewaters containing high levels of ethers and ethanol. However, it is also possible that spikes of extremely low quality can be caused by process interruptions such as power failure, fire, flood, storms, over- or under-loading of wastewater treatment systems, temporary unavailability of wastewater holding dam capacity and the absence of trained operators. 9,10,11 In South Africa, the production of wine can be divided into various stages. Bottling and washing of tanks and other equipment takes place during the pre-harvest period. 10 The generation of winery wastewater increases substantially from early harvest onwards, and the production of white wine dominates harvest activities. The peak harvest period, which generates the largest quantity of the wastewater, can last up to 14 weeks. During late harvest, wastewater generation decreases substantially and red wine production dominates the harvest activities. In the post-harvest period, pre-fermentation

wastewater, particularly during harvest. This wastewater contains high levels of potassium (K) and sodium (Na). Since water resources are limited, wine grape producers will have to use them judiciously to produce grapes. In this regard, it is also important that the sustainable use of alternative water sources for vineyard irrigation be investigated. The primary objective of the study was therefore to assess the fitness for use of winery wastewater for irrigation of different soil types with varying rainfall quantities and leaching levels on vineyard performance in terms of yield and quality under field conditions, as well as measuring the change in mainly Na and K status of soils. Grapevines growing in the regions with lower mean annual rainfall required more irrigation. Results showed that the K and Na levels in the undiluted winery wastewater was substantially higher than that in the raw water. Therefore, the potassium adsorption ratio (PAR) of the undiluted winery wastewater was substantially higher than the raw water. Considering that results confirm that winery wastewater contains high levels of K, the use of the PAR of the wastewater should be considered as a further indicator of the wastewater quality. Substantial amounts of additional elements were applied to the vineyard via the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation. As the amounts of K applied via the in-field fractional use (augmentation) of winery wastewater with raw water were considerably higher than the grapevine’s requirements, the cultivation and removal of a suitable interception crop during summer might be useful to absorb excessive K.

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TECHNICAL YEARBOOK 2024