Production, recovery and reuse of biogenic elemental selenium

Selenium (Se) has caused several ecological disasters due to its toxicity and bioaccumulation along trophic networks. Industrial activities that process fossil fuels and mineral ores, such as electricity generation, metal extraction and oil refining, produce wastewaters containing selenium. Currently, these wastewaters are insufficiently treated before being discharged into the environment. Several environmental biotechnological processes are used to convert soluble selenium oxyanions, selenite and selenate, to solid elemental selenium, Se(0), because elemental selenium is less toxic. Applying a post-treatment solid–liquid separation step to these biological processes removes and separates Se(0) from the treated effluent. Here, we review the sources of selenium-rich waste streams, and we propose several techniques for the removal and reuse of selenium. The major points are as follows: (1) Biogenic Se(0) has colloidal properties that can be offset by the addition of coagulants, either by dissolving multivalent salts or by electrogenerating the coagulant in situ; (2) recovered biogenic Se(0) is a secondary raw material and (3) biogenic Se(0) can be used for niche applications such as fertilizers and adsorbent for metals. The biological treatment of industrial wastewater containing selenium can be linked with resource recovery as a sound and economic approach to alleviate the demand for this critical element.