IntroductionSelenium, first discovered in 1818, is a metalloid and chalcogen. It has multiple oxidation states, beginning with the most reduced state, namely selenate (SeO 4 2-, Se(VI)), followed by selenite (SeO 3 2-, Se(IV)), elemental selenium (Se 0 , Se(0)) and finally selenide (Se 2-). Of the selenium released into the environment, 37.5-40.6% can be ascribed to anthropogenic activities. It is released from the earth's crust by the mining of coal and various metals, oil production, use of agricultural products, as well as during the melting of non-ferrous metals [1]. Landfill ash disposal that generates toxic leachate poses a risk of groundwater contamination, which leads to the polluting of nearby water bodies [2].Selenium is mostly present in water as selenate or selenite. According to different studies, acid mine drainage waters contain selenium at concentrations ranging between 2 × 10 -4 and 6.2 × 10 -3 mM of total selenium [3]. Waste water from oil refineries in the San Francisco Bay (USA) contains relatively low concentrations of selenium of about 50-300 µg. L -1 [4]. The waste water from a selenium refinery plant in Japan contained an average of 30 mg. L -1 selenium, with the majority of the selenium present as selenite [4].The upward trend in energy production from coal, along with the burning of fossil fuels contribute to this increase in selenium release. The high concentration of these selenium oxyanions poses a problem to the environment, since they are toxic and bio-accumulate readily. In one case it was found the concentration of selenium in the apex predators (birds and humans) in the area were 2 000 times higher than in the water [4]. Elemental selenium is not soluble in water and thus has a much lower bio-availability than the oxyanions. Elemental selenium's toxicity is also much lower than that of the oxyanions [1]. AbstractBioremediation of seleniferous water is gaining more momentum, especially when it comes to bacterial reduction of the selenium oxyanions. More and more bacterial strains that are able to reduce selenium are being isolated. These bacteria need to be studied further to determine whether they are suited for industrial application. In this study, the reduction of Se(VI) to Se(0) by Pseudomonas stutzeri NT-I was examined using batch experiments with the bacteria suspended in MSM. For the determination of the optimum conditions for the growth of the bacteria, the linearized rate during the exponential phase for different conditions were compared. A pH 7, temperature of 37°C, salinity of 20 g.L -1 NaCl and initial concentration of 5 mM selenate were found to be the best at promoting growth. To determine the optimum conditions for the reduction of selenium, the amount of Se (0) recovered from the plug after 16 hours of incubation was measured. A pH of 8, temperature of 37°C and salinity of 5 g.L -1 resulted in the most Se (0) recovered. The kinetics of the reduction of Se(VI) to Se (0) was found to follow the adapted Monod equation. An increase in the initial Se(VI) concentrati...