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A Technical Guide for Wine Producers
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Management of ponds for the treatment of cellar wastewater
Charl Theron
The importance of handling cellar wastewater cannot be emphasised enough. Winemakers must realise that their responsibility in this regard is not secondary to vinification, instead it is a very real responsibility as a direct by-product of vinification. For some time now Australian and Californian cellars have been implementing specific practices.
A basic goal of effluent management is conservation of the environment and the potential recycling of water. This can only be achieved by reducing the organic content of cellar wastewater. This content consists of dissolved sugar, alcohol, acids, polyphenols, tannins and lignins, all of which derive from the vinification process. The biological dissolution of the compounds has long been the preferred method and the wastewater treatment pond may serve as a reactor in which bacteria convert the wastewater to solids, carbon dioxide and water. The use of properly managed ponds for the treatment of cellar wastewater has long been a popular, acceptable method of processing cellar effluent.
The effective operation of such ponds depends on control over the factors that influence the microbial growth in the pond. This mainly entails the availability of sufficient substrate and oxygen. Once these two requirements have been met, factors such as pH and the availability of nutrients may also come into play. Bacteria in particular, especially specific species, play an important role as microbes. It is therefore also important to conduct a microscopic evaluation from time to time so as to monitor the micro-stability of the system.
Excessive growth of algae often occurs in cellar wastewater treatment ponds. This may cause the irrigation equipment handling the effluent to become blocked or polluted. Excessive growth of algae may also cause the available oxygen to become exhausted, which may impact on the bacteriological dissolution process and could also promote the formation of off-odours. Ways to facilitate the management of algae growth is to identify the species of algae, adapt aeration practices and supplement nutrients.
Treatment ponds are flow systems and their size, in conjunction with the influx of wastewater, will determine whether sufficient reaction time is available for the bacteriological breakdown of the organic load in the cellar's wastewater. A reduction in the wastewater volume as a result of effectively applying water conservation practices will obviously increase the contact period in ponds. This may then result in improved treatment or enlargement of the pond's capacity. In the same vein a reduction in the saline quality of the wastewater will be beneficial. Cellars should use potassium rather than sodium based solutions to clean cellar equipment and peracetic substances should be used for sanitation. By using the latter a final rinse with water is not required and in conjunction with the reduction in salinity through the use of potassium soda substances, it may impact very positively on the volume and quality of cellar wastewater.
In order to determine the capacity of wastewater treatment ponds, allow approximately 60 to 90 days' reaction time during the peak period for the cellar wastewater breakdown process. Also make allowances for sufficient additional capacity in case of wet weather conditions.
The choice of suitable aeration equipment will determine the extent of the capital and operational expenses. The most important consideration in this regard is the effectiveness of the equipment to ensure that sufficient oxygen is diffused in the water and effectively mixed with the organic matter and bacteria. The amount of oxygen required is relative to the organic load that gets dumped in the pond during the peak period of the cellar. Usually 1,0 mg/l dissolved oxygen will suffice, but it is safer to maintain 2,0 mg/l so as to prevent potential problems during the peak period.
Apart from the cardinal roles played by the capacity of the pond and the effectiveness of the aeration process, the following important factors may also come into play:
A pH of 6,5 to 8,5 must be maintained and suitable additions made, if required.
Apart from carbon dioxide, the breakdown bacteria also require nutrients such as nitrogen and phosphates. Applicable additions may sometimes be required, but as excessive amounts of ammoniac nitrogen, chloride and heavy metal concentrations may limit bacterial growth, additions should be determined analytically.
Extreme temperatures of cellar wastewater are detrimental to the effectiveness of the bacteriological process and higher temperatures also require more aeration. The capacity of the treatment pond will obviously determine the average temperature of the content.
The solids in cellar wastewater will not only increase the organic load of the effluent, but in due course of time they will also reduce the capacity of the treatment pond. It is therefore recommended to use sieves with a net size of 250 to 3 000 micron to remove the solid particles. If the removal of cellar lees, filtration aids and bentonite is not effective by such means, other practices should be considered, such as lees filtration, finer sieves or gravitational settling.
The systematic management of the cellar pond(s) for the treatment of wastewater could very well ensure the successful implementation of this processing method.
Reference:
Dombeck, G, 2005. Managing Your Wastewater Treatment Pond. Wine Business Monthly. March 2005: 35 - 40.
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