Microbial selenium sulfide reduction for selenium recovery from wastewater

• Published in: Journal of hazardous materials Vol. 329; pp. 110 - 119
• Main Authors: Hageman, S.P.W., van der Weijden, R.D., Stams, A.J.M., van Cappellen, P., Buisman, C.J.N.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 05-05-2017
• Subjects: Biocrystallization; Microbial reduction; Selenium removal and recovery; Selenium sulfide; Wastewater; Biocrystallization; Microbial reduction; Selenium sulfide; Selenium removal and recovery; Wastewater
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2016.12.061

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•Selenium sulfide is bio-reduced to selenium and sulfide by mixed cultures.•Selenium particles have a high selenium purity and are hexagonal crystalline.•Se particles are outside the biomass and this is beneficial to recover Se from water.•Produced sulfide is recycled in the selenium recovery system.•SeS2 bio-reduction and SeS2 precipitation conditions can be altered independently.
Microbial reduction of selenium sulfide (SeS2) is a key step in a new treatment process to recover selenium from selenate and selenite streams. In this process, selenate is first reduced to selenite, and subsequently selenite is reduced by sulfide and precipitates from the solution as SeS2. The latter is bio-reduced to elemental selenium and sulfide. Two anaerobic granular sludges (Eerbeek and Emmtec) were tested for their efficiency to reduce commercial crystalline SeS2. Emmtec sludge had the highest reducing capacity with commercial SeS2 and was therefore also used for the bioreduction of laboratory synthesized amorphous SeS2. Synthesized SeS2 was formed mixing a sulfide solution and effluent containing selenite. With both SeS2 solids (commercial and synthesized SeS2), Emmtec sludge produced sulfide and a solid consisting of hexagonal elemental selenium. The crystalline hexagonal structure suggests the absence of biomolecules, which stabilize amorphous selenium bio-particles under comparable process conditions (T=30°C and a pH between 6 and 7). Selenium particles were not attached to the biomass, suggesting an extracellular formation. The results support the feasibility of the bio-reduction process using sulfur for recovering selenium from water.