Selenium (Se) is a naturally occurring trace element that is nutritionally essential for humans and animals, but becomes toxic at high concentrations. This laboratory study explored the role of microbes in Se removal from contaminated wastewater via biological transformation and volatilization processes. Microbes could immobilize water-soluble selenate (SeO 4 2- ) and selenite (SeO 3 2- ) to water-insoluble elemental Se (Se 0 ) and transform Se into volatile Se compounds found in the atmosphere. Results of this laboratory study showed that Bacillus cereus, a bacterial strain isolated from wheat straw and biosolid-WTR-sand substrates showed a significant biotransformation ability of reducing selenate and selenite to elemental Se and forming volatile Se organic compounds in wastewater. Overall, microbial Se chemical reduction, methylation, and volatilization are important processes in bioremediation of Se-contaminated wastewater.