Wastewater is considered to be the most important aspect at wine cellars that can result in detrimental effects on the natural environment.
National legislation and foreign markets require responsible management of potential negative environmental impacts (Van Schoor, 2001). Various research projects are being conducted worldwide to address disposal of winery wastewater in environmentally friendly ways (Van Schoor, 2000). In South Africa, more than 90% of wine cellars dispose of their effluent by means of land application, mainly irrigation. Land application is currently considered to be the most effective and practicable disposal method for water, nutrient and organic matter contents of winery effluent (Ryder, 1995). The objective of this article is to highlight the environmental impact of organic substances from winery effluents, as determined during a multi-disciplinary study carried out at ARC Infruitec-Nietvoorbij (Mulidzi, 2001).
Procedures and results
Soil profiles from effluent disposal sites at ten wineries were examined during 2000. At three wineries, where disposal was done on sandy soils, the results indicated that the organic matter component of the effluent leached through the soil to the level of the water table. The findings from these three wineries are discussed here.
During May 2000, a soil profile was exposed at the first winery, where effluent disposal was done by irrigating kikuyu grass. Irrigation penetrated to a depth of 1 m, at which depth the soil became very wet. At 1,2 m a water table was reached. From the soil surface to 1,2 m deep the soil was light gray, almost white sand. However, the sand became black at the upper extremity of the water table. This black sand had a strong, unpleasant odour indicating that anaerobic decomposition was taking place.
During November 2000, long after the 2000 vintage season had ended, this black layer was 0,6 m thick, extending from 1,2 to 1,8 m below the soil surface. A sample of the black soil was washed in the laboratory by repeatedly adding water, stirring, and decanting the supernatant liquid.
The result was white sand, identical to the soil above the water table, and a black liquid (Plate 1). This demonstrated that the black material was organic matter, which, in this situation, could only have been supplied by the effluent. Investigations carried out in a drainage ditch at the lower end of the effluent disposal area revealed the presence of substantial quantities of black gel-like organic material (Plate 2). The organic material was therefore being transported from the disposal site by lateral subsurface water movement. As the ditch emptied into a nearby stream, this organic matter, which originated from winery effluent, constituted a pollution hazard. The results from the investigation at this site can be summarised as follows:
a.Organic matter from the winery effluent moved down through the soil to the water table. It was then transported laterally to an open watercourse, at which point it constituted an ongoing pollution hazard.
b.Provided that the soil at the disposal site remained undisturbed, no unpleasant odour was evident. Only when the soil was disturbed, sulphurous (rotten egg) odours, that are indicative of anaerobic decomposition, became evident.
c.The fact that the thick, black layer remained several months after the disposal of the effluent indicates that the rate at which the organic material decomposes under the prevailing anaerobic conditions is very slow.
d.A possible reason why the problem had not been identified previously was that the top of the black layer occurred at a depth of 1,2 m, whereas sampling was usually carried out to a depth of around 0,9 m. Deeper sampling is obviously necessary.
At the second winery, where disposal is also by means of irrigating kikuyu grass, a similar situation to that at the first winery was found during an investigation in May 2000. At this winery, however, the top of the water table was only 0,8 m beneath the soil surface and lateral drainage carried organic material from the effluent directly into the river. Thick layers of black, organic coagulates were found in the stream, extending some distance downstream from the point of entry.
At the third winery, where disposal is carried out by means of ponding on a deep, well-drained sandy soil, there was no sign of organic matter accumulation to a depth of 2 m. A black layer was present in water-saturated soil at 2,1 m. The layer was considerably thicker than at the first winery and the unpleasant odour was stronger, more pervasive and more obnoxious. Again the odour remained undetected as long as the black layer was not exposed. Although the disposal site is not close to a stream, the water table at the disposal site is likely to link with other, neighbouring water bodies. The potential therefore exists for pollutants to be spread over a wide area, possibly affecting boreholes or streams some distance from the point of origin.
From the results of these investigations it is clear that the organic component of winery effluents does not benefit the soil to which it is applied. It is, in fact, not retained by the soil and poses a serious pollution hazard to any water body into which it may be carried.
Winery effluents pose severe pollution problems, mainly because the organic component leaches down to the water table where decomposition is slow, due to the shortage of oxygen. Unpleasant odours are released if the soil is disturbed. The organic material is mobile in the ground water and constitutes a major off-site pollution hazard. This is aggravated by the fact that disposal at all three sites was carried out on sandy soils with low nutrient retention and water storage capacities, and high permeabilities. Large volumes of effluent are often discharged on small areas of land, which aggravates leaching. Some of the disposal areas were closer than the permissible distance to streams.
Many wineries have few alternatives regarding the area of land available for effluent disposal, the type of soil, or even the location of that land. Effluent disposal and its associated off-site pollution nevertheless remain the problem and must be addressed urgently. It is possible that wetlands, which involve the movement of water through reed beds, may prove to be an effective way of purifying winery effluent. The use of a Constructed Wetland to purify winery and distillery effluent is currently being investigated at ARC Infruitec-Nietvoorbij.
It is recommended that studies of effluent quality, effluent disposal and disposal site characteristics should be made at as many wineries as possible and that the effects of pollutants on aquatic life should also be investigated, and toxic concentrations determined.
Mulidzi, A R. 2001. The environmental impact of winery effluent in the Northern and Western Cape Provinces. M. Inst. Agrar Thesis, University of Pretoria. 128 pp.
Ryder, R A. 1995. Aerobic pond treatment of winery wastewater for vineyard irrigation by drip & spray system in California. Rev. Fr. Oenol 152, 22-24.
Van Schoor, L H. 2000. Management options to minimize negative environmental impacts at wine cellars. Wineland, July, 97-100.
Van Schoor, L H. 2001. Environmental legislation in the viticultural and wine industry. Wineland, January, 114 – 117.
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About the Authors:
Reckson Mulidzi1, Giel Laker2, Lourens van Schoor1 and Kobus Louw1
1ARC Infruitec-Nietvoorbij, Stellenbosch.
2Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria.