Nomination for microbial selenium crystal recovery from waste streams

Simon Hageman, former Ph.D. scientists at ETE, has been nominated, for the KNCV Piet Bennema Prize for Crystal Growth 2018. The prize is awarded every 3 years to a young scientist that has published high-level scientific research in the field of crystal growth in an industrial context. Hageman is one of 3 nominees and although he finally did not win the price, his nomination proves the relevance of his research.

Precious resource
Selenium is present in several waste streams from the industry, for example in emission gases from coal plants. These gases are washed before release, and as a result selenium ends up in waste water. Recovery of this precious resource is needed to save costs and prevent pollution. Hageman developed a method for the efficient removal of this compound using microorganisms. ‘There are two different oxidized forms of selenium in wastewater: selenate and selenite’, Hageman says. ‘At higher temperature, around 50 °C, or a pH above 8, microorganisms convert selenate into selenium crystals that can be recovered in a cost-effective way.’

Simple recovery
But Hageman also developed a procedure to recover selenium from wastewater that worked around 30 °C and neutral pH. Instead of selenate, the other form of selenium, selenite, was converted into selenium crystals in several steps. Again, microorganisms played a key role. Sulphide, formed by microorganisms in waste streams, react with selenite to form seleniumsulphide. That compound precipitates, where after other microorganisms present in sludge subsequently convert seleniumsulphide back into sulphide and crystalline selenium. The selenium crystals formed were relatively large, in the order of micrometers, allowing a simple recovery. ’The elegance of this method is that due to the lower temperature needed energy is saved, while sulfide is recycled during the reaction’, Hageman says. ‘Also, the relatively large selenium crystals can be recovered even more easily.'

Ph.D. Thesis: Bio-induced solid selenium for recovery from water, 148 pages ISBN 978-94-6257-510-3