Bacterial reduction of selenate to elemental selenium utilizing molasses as a carbon source

Selecting an inexpensive and effective organic carbon source is the key to reducing the cost in selenium (Se) remediation. Five bacteria were screened based on their ability in using molasses as an organic carbon source to reduce selenate [Se(VI)] in drainage water. Efficiency of Se removal differed in the molasses-added drainage water containing different bacteria, with an order of Enterobacter taylorae > Pantoea sp. SSS2 > Klebsiella sp. WRS2 > Citerobacter freundii > Shigella sp. DW2. By using E. taylorae, 97% of the added Se(VI) (1000 μg/L) was reduced to elemental Se [Se(0)] in an artificial drainage water during an 11-day experiment, and 93% of Se(VI) in a natural agricultural drainage water was reduced to Se(0) and organic Se during a 7-day experiment. E. taylorae also rapidly removed Se(VI) in agar-coated sand columns. During 45 days of the experiment, more than 92% of influent Se was removed from the drainage water with a molasses range of 0.01–0.1%. This study reveals that molasses may be a cost-effective organic carbon source used by Se(VI)-reducing bacteria to remove Se from agricultural drainage water in field.