A method of removing or reducing the concentration of a contaminant in wastewater. The method involves combining wastewater and an elemental iron, comprising of zero valent iron, in a tank to produce treatment water. In this method the wastewater contains a contaminant consisting of: selenate [Se(VI)], selenite [Se(IV)], selenocyanate [SeCN−1], selenide [Se(−II)], and combinations thereof. The treatment water is then agitated with mechanical mixing and air sparging to produce a treated slurry. The treated slurry is then separated into a treated water stream and a contaminate stream.