In-field fractional use of winery wastewater with raw water (Part 2): Irrigation application, water quality and nutrient load

Abstract

Wineries produce large volumes of poor quality 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.

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 activities come to an end and maximum usage of hydroxide occurs. Beyond the harvest, wastewater production is at its lowest. The major origin of winery wastewater is water used for cleaning processes and makes up approximately 78% of the wastewater generated. This water is from alkaline washing, neutralisation and rinsing water used for tanks, floors, transfer lines, bottles and barrels. These actions will increase the Na, K and H₂PO₄^– levels in the wastewater, consequently there will be a variation in pH and an increase in electrical conductivity (EC), chemical oxygen demand (COD) and SAR.

Regarding the legal requirements for irrigation water quality in South Africa,^12,13 COD, pH, EC and SAR are considered to be important. Results from a survey carried out to evaluate winery wastewater generated by South African wineries showed that the water quality parameters vary substantially between wineries.¹⁴ Furthermore, there was a strong seasonal variation in the winery wastewater quality. A similar seasonal trend was reported for winery wastewater in Australia.¹⁵ These trends were confirmed where wastewaters of two wineries were monitored frequently.¹⁶

In this specific article the irrigation application, water quality and nutrient load will be presented. In brief, the primary objective of the project was 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.

Methods

At most of the experimental plots, grapevines were irrigated with the in-field fractional use (augmentation) of winery wastewater with raw water from mid-February when suitable wastewater became available from vintage processes. According to this approach, grapevines were irrigated as follows.⁵ For each irrigation, 50% of the irrigation requirement was applied as undiluted winery wastewater. Raw water was applied for the other 50% of the irrigation requirement. The application of irrigations was stopped either in mid-April or the beginning of May each year when the winter rainfalls began. Irrigation was applied by means of micro-sprinklers in order to apply larger volumes of water. It should be noted that experimental grapevines were irrigated so that optimum wine quality would be obtained. Therefore, stem water potential (Ψ_S) thresholds for optimum wine quality for the specific cultivars were used to set up the irrigation refill lines. Water meters were used to monitor the irrigation volumes of winery wastewater and raw water applied to each experimental plot.

The soil water content (SWC) was measured by means of the neutron scattering technique. Three access tubes were installed on the grapevine row at each of the six experimental plots at the beginning of the project. The mean SWC of each experimental plot was calculated as the average of SWC measured at the three individual access tubes. Measurements were taken in 30 cm increments up to a depth of 90 cm in all experimental plots and up to 180 cm in plots where deeper measurements were possible. Measurements were taken every two to three weeks, as well as before and after every irrigation application.

Approximately one hour after the in-field fractional use (augmentation) of winery wastewater with raw water commenced, a 2 L sample of the undiluted winery wastewater was collected. A sample was also collected when the raw water was applied. Samples were analysed for COD at ARC. They were also analysed by commercial laboratories (Bemlab, Strand and Labserve, Stellenbosch) according to previously reported methods.¹⁷ The potassium adsorption ratio (PAR) and SAR of the water samples was calculated.

For each irrigation, the amount of raw and winery wastewater applied, as well as the element concentrations in the undiluted winery wastewater and raw water were used to calculate the amounts of elements added to the soil per irrigation per hectare. The amount of elements applied per irrigation, i.e. the undiluted winery wastewater irrigation plus the raw water irrigation, were summed to obtain the seasonal applications.

Results

Irrigation application

In the 2017/18 season, two irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the loamy sand (C1) and sandy clay loam (C2) experimental plots in the Coastal region. Two irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the sandy loam (BR1) and sandy clay loam (BR2) experimental plots in the Breede River region. Five and six irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the deep sand (LOR1) and shallow sand (LOR2) experimental plots in the Lower Olifants River region, respectively.

In the 2018/19 season, two raw water irrigations and three irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the C1 experimental plot (Figure 1). Three irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the C2 experimental plot. Three and two irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the BR1 and BR2 experimental plots, respectively. The in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation commenced at the LOR1 and LOR2 experimental plots at the beginning of the season. In total, four irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the LOR1 experimental plot. Visual observations in the LOR2 vineyard (Figure 2) in November 2018 revealed that the grapevines were growing poorly. After consideration of the EC of the undiluted winery wastewater, it was decided to decrease the ratio of winery wastewater to raw water at this specific plot. In this regard, from December 2018, a ratio of 25% winery wastewater to 75% raw water was applied, i.e. a fractional ratio of 0.25. In total, nine irrigations were applied to the grapevines growing in the LOR2 experimental plot (Figure 3).

FIGURE 1. Variation in soil water content (SWC) during the 2018/19 season where the in-field fractional use (augmentation) of winery wastewater with raw water was used to irrigate young Cabernet Sauvignon grapevines in the C1 plot [P is precipitation, I_r is raw water irrigation, and I is where the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation was applied].

FIGURE 2. Grapevine vegetative growth at the end of November 2018 (A) in the LOR2 experimental plot where the in-field fractional use (augmentation) of winery wastewater with raw water was used for vineyard irrigation, and (B) the block section adjacent to the experimental plot which was irrigated by the producer.

FIGURE 3. Variation in soil water content (SWC) during the 2018/19 season where the in-field fractional use (augmentation) of winery wastewater with raw water was used to irrigate Cabernet Sauvignon grapevines in the LOR2 experimental plot [I is where the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation was applied].

In the 2019/20 season, two raw water irrigations and three irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the C1 and C2 experimental plots. Five raw water irrigations and two irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the BR1 and BR2 experimental plots. Six raw water irrigations and four irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the LOR1 experimental plot. Given the extremely poor performance of the grapevines after two seasons of being irrigated according to the in-field fractional use (augmentation) of winery wastewater with raw water at the LOR2 experimental plot, wastewater irrigation at this particular experiment plot had to be terminated from the beginning of the season to prevent any further damage. Salt deposits on the lower section of the grapevine trunks in the LOR2 experimental plot were clearly visible in September 2019 (Figure 4). Thereafter, the vineyard was irrigated according to the grower’s schedule to facilitate the recovery of the grapevines.

FIGURE 4. Example of salt deposits on the lower section of grapevine trunks in the LOR2 experimental plot in September 2019.

In the 2020/21 season, winery wastewater was only available at the Coastal region plots from early February 2021. Therefore, until then, where the experimental plots required irrigation, they were irrigated with raw water. As soon as wastewater became available at these sites, the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation commenced. Four and three raw water irrigations were applied to the C1 and C2 experimental plots, respectively. Four irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the C1 and C2 experimental plots. Four raw water irrigations and two irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied to the BR1 and BR2 experimental plots. Eight raw water irrigations and two irrigations using the in-field fractional use (augmentation) of winery wastewater with raw water were applied at the LOR1 experimental plot. The LOR2 experimental plot was still irrigated according to the grower’s schedule to facilitate the recovery of the grapevines.

Water quality

In the Coastal region, the average pH, EC and COD of the undiluted winery wastewater applied using the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation over four seasons was 5.53, 1.28 dS/m and 2 440 mg/L, respectively. The average Na, K, Ca and Mg content of the winery wastewater was 34 mg/L, 303 mg/L, 25 mg/L and 8 mg/L, respectively. The average SAR and PAR of the winery wastewater was 1.57 and 8.03, respectively. The average pH, EC and COD of the raw water over four seasons was 7.00, 0.18 dS/m and 3. The average Na, K, Ca and Mg content of the raw water was 19 mg/L, 3 mg/L, 7 mg/L and 4 mg/L, respectively. The average SAR and PAR of the raw water was 1.45 and 0.12, respectively.

In the Breede River region, the average pH, EC and COD of the winery water applied using the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation over four seasons was 5.49, 1.17 dS/m and 4 445 mg/L, respectively. The average Na, K, Ca and Mg content of the winery wastewater was 29 mg/L, 171 mg/L, 38 mg/L and 14 mg/L, respectively. The average SAR and PAR of the winery wastewater was 1.02 and 3.51, respectively. The average pH, EC and COD of the raw water over four seasons was 6.84, 0.24 dS/m and 3 mg/L, respectively. The average Na, K, Ca and Mg content of the raw water was 25 mg/L, 2 mg/L, 7 mg/L and 6 mg/L, respectively. The average SAR and PAR of the raw water was 1.65 and 0.08, respectively.

In the Lower Olifants River region, the average pH, EC and COD of the winery wastewater to the LOR1 experimental plot over four seasons was 6.27, 3.07 dS/m and 5 546 mg/L, respectively. The average Na, K, Ca and Mg content of the winery wastewater was 77 mg/L, 557 mg/L, 327 mg/L and 22 mg/L, respectively. The average SAR and PAR of the winery wastewater was 1.26 and 5.22, respectively. The average pH, EC and COD of the raw water over four seasons was 6.78, 0.19 dS/m and 9 mg/L for the LOR1 experimental plot, respectively. The average Na, K, Ca and Mg content of the raw water applied to this experimental plot was 22 mg/L, 2 mg/L, 5 mg/L and 4 mg/L, respectively. The average SAR and PAR of the raw water was 1.71 and 0.10, respectively.

The average pH, EC and COD of the winery wastewater applied to the LOR2 experimental plot over two seasons was 5.75, 3.21 dS/m and 8 535 mg/L, respectively. The average Na, K, Ca and Mg content of the winery wastewater was 240 mg/L, 402 mg/L, 184 mg/L and 26 mg/L, respectively. The average SAR and PAR of the winery wastewater was 5.12 and 4.91, respectively. The average pH, EC and COD of the raw water applied to the LOR2 experimental plot over two seasons was 6.65, 0.20 dS/m and 28 mg/L, respectively. The average Na, K, Ca and Mg content of the raw water was 19 mg/L, 2 mg/L, 4 mg/L and 5 mg/L, respectively. The average SAR and PAR of the raw water was 1.49 and 0.11, respectively. The average pH and EC of the raw water applied to the LOR2 experimental plot after the termination of the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation at the beginning of the 2019/20 season was 6.82 and 0.19 dS/m, respectively. The average Na, K, Ca and Mg content of the raw water was 26 mg/L, 3 mg/L, 5 mg/L and 4 mg/L, respectively. The average SAR and PAR of the raw water was 1.67 and 0.13, respectively.

Nutrient load

The concentrations of each element applied via the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation were used to calculate the amount of each element applied. On average over four seasons, 259 kg/ha, 38 kg/ha, 15 kg/ha and 71 kg/ha of K, Ca, Mg and Na, respectively, were applied per season to each of the experimental plots in the Coastal region. In the Breede River region, 108 kg/ha, 48 kg/ha, 29 kg/ha and 114 kg/ha of K, Ca, Mg and Na, respectively, were applied per season to each of the experimental plots. On average over four seasons, 844 kg/ha, 496 kg/ha, 56 kg/ha and 225 kg/ha of K, Ca, Mg and Na, respectively, were applied per season to the LOR1 experimental plot in the Lower Olifants River region. For the LOR2 experimental plot, 958 kg/ha, 470 kg/ha, 79 kg/ha and 631 kg/ha of K, Ca, Mg and Na, respectively, were applied per season.

Conclusions

As expected, grapevines growing in the regions with lower mean annual rainfall required more irrigation. The K and Na levels in the undiluted winery wastewater was substantially higher than that in the raw water. Consequently, the PAR of the undiluted winery wastewater was substantially higher than the raw water. With regard to the refinement of the General Authorisations for wineries, the PAR of the wastewater has not yet been adopted as a quality parameter. 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. However, further research is needed to refine PAR norms for wastewater quality. Taking above-mentioned into consideration, 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. Given that 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.

Soil responses to the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation will be presented in the next article.

Acknowledgements

• This article is an output of WRC Project K5/2561, entitled “Use of winery wastewater as a resource for irrigation of vineyards in different environments”. This solicited project was initiated, funded and managed by the WRC. The project was co-funded by Winetech and ARC.
• ARC for infrastructure and resources.
• Staff of the Soil and Water Science division at ARC Infruitec-Nietvoorbij for their assistance, and in particular Mr. F. Baron for his dedicated technical support.
• Backsberg, Madeba, Lutzville Winery and Spruitdrift Winery for permitting the project team to work at their wineries and in their vineyards. Colleagues at the wineries for their assistance and support.
• W. Smit from Netafim for advice and designing the irrigation systems.

References

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For more information, contact Carolyn Howell at howellc@arc.agric.za.

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