A Technical Guide for Wine Producers

RECENT ARTICLES   |   WYNBOER HOME Wetlands consistently clean up organic effluents Keith du Plessis Keith du Plessis, LNR Infruitec-Nietvoorbij, Stellenbosch In view of increasingly stringent wine industry controls on wastewater quality, and of the scarcity of water as a resource, compounded by uncertainties over global warming and its effects, the recent completion of a Ph.D. thesis on the use of artificial wetlands to purify distillery and winery waste water is both welcome and timely. The study, which was initiated at Distell's Goudini distillery in the Western Cape, set out to explore the possibility of using constructed wetlands to treat distillery wastewater. Initial findings showed that artificially constructed wetlands do, indeed, have the ability to treat distillery wastewater providing that the chemical oxygen demand of the effluent does not exceed 15 000 mg/L, and are able to do so over protracted periods of time provided that the correct substrate materials are used. Nr. 1 - Lab-scale constructed wetlands (50 cm long x 40 cm high x 30 cm wide) made out of perspex. The substrate material is ~2 mm diameter gravel and is planted with Typha sp. plants. Nr. 2 - Lab-scale constructed wetland that is under stress. Nr. 3 - Lab-scale set-up. Wastewater are pumped from a settling tank into the wetland via an inlet pipe which extends to the bottom of the tank. From there it is pushed through the tank, which has a 1% slope to the outlet, and into a holding section at the outlet of the system. Nr. 4 - Healthy lab-scale wetland. Nr. 5 - Microbial colonisation on a piece of gravel isolated from a constructed wetland. Having established the viability of the process, further studies were carried out with the aim of improving our understanding of the microbial ecology of artificial wetlands, and of the factors that control them. The objective of this, second, phase was to find ways of improving the efficiency of wastewater treatment in constructed wetland systems. Amongst others, the organisms investigated included protists (mobile, single celled grazing organisms), whose activities may, at times, cause slime to be generated which clogs pores in the substrate, slowing effluent movement and degradation, and algae, which, in light, increase the pool of nutrients, and of oxygen, which are available to the bacterial and yeast members of the community. These studies revealed that, far from being uniform and reasonably static, microbial communities in artificial wetlands are highly dynamic. Communities varied between zones in the same wetland, between different wetlands, and between communities sampled from the same zone at different times. Notwithstanding this microbiological variability, artificial wetlands were consistently able to remove, or to degrade, the materials that create a demand for oxygen, resulting in decreases in chemical oxygen demand of up to 90%. Work which is still gaining momentum concerns the identification of species of micro-organism which are exceptionally efficient at breaking down organic effluents. That such organisms exist, is strongly suggested by the results of trials in which wetland microbial communities were augmented with concentrated ferments of microbes derived from the wetlands themselves. Collectively, results obtained to date indicate that, in terms of their effectiveness in breaking down distillery and, by inference, winery effluents, the microbiological communities in artificial wetlands are remarkably robust. This bodes well for the many branches of agricultural in which organic effluents are generated. For further information please contact Keith du Plessis, tel (021) 809-3158, e-mail dplessisk@arc.agric.za.

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