Abstract: Dissolved selenium is removed from water by treatment in a reactor containing microbial biomass to cause the hexavalent selenium to be converted to forms of selenium which can be readily removed from the water, and causing or allowing the removable forms of selenium to be removed from the water. Examples of removable forms of selenium include volatile organic selenium compounds, volatile inorganic selenium compounds, elemental selenium, entrainable organically-complexed selenium compounds, entrainable tetravalent selenium compounds, and entrainable bivalent selenium compounds. The volatile selenium compounds can be removed and recovered as a gas, while the entrainable forms of selenium can be entrained by larger particles and separated off, for example by filtration.