Biological removal of copper ions from distillery waste

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Nikolaos Pantidos, David Arnot and Louise Horsfall

University of Edinburgh, United Kingdom

Many nonferrous industries such as mining and surface treatment plants produce co-products that are high in heavy metals and therefore toxic to the environment. A less obvious producer of heavy metal co-products is the whisky industry. Current methods of copper removal from such co-products include electrolysis and membrane filtration which are reported to be impractical and costly. Alternatively, when copper is found as a salt, current methods of removal include settlement, filtration and precipitation. Biological copper ion removal from effluents has been shown to be quite effective.

There are two biological methods to remove copper from effluent which involve biosorption and reduction. Biosorption involves bacteria binding to copper via the cysteine-rich transport proteins that are associated with the cell membrane to precipitate it. Some bacteria are also able to reduce higher valency insoluble copper ions into lower valency insoluble forms of the metal. An example of such a bacterium is Thiobacillus ferrooxidans which is able to reduce Cu2+ to Cu+ using SFORase. The Cu+ ions can then be mixed with a compound to produce an insoluble salt which precipitates and can easily be removed.

Although T. ferrooxidans is able to reduce copper to a lower valency state, it is slow growing with a replication time of 5.2 hours which makes it not very ideal for industrial use. Therefore it is possible to transfer these genes to a faster growing organism such as E. coli using synthetic biology techniques. There is also the possibility to improve the copper reduction effectiveness by modifying the genes responsible for this process. This will potentially yield an organism that is both fast growing and able to reduce copper to an insoluble form in order to precipitate it from solution.