Chromium(VI) bioreduction and removal by Enterobacter sp. SL grown with waste molasses as carbon source: Impact of operational conditions

Abstract

A technology utilizes bacteria Enterobacter sp. SL grown in an anaerobic reactor with waste molasses as carbon source to bio-reduce hexavalent chromium [Cr(VI)] in wastewater and then remove total chromium has been developed. The performance was elucidated through different initial and operating experiments conditions, and the associated mechanism of Cr(VI) reduction was explained. Results show that Cr(VI) removal is 99.91% at 25 h in the anaerobic reactor initially containing bacteria of 5% (v/v), (NH<inf>4</inf>)<inf>2</inf>Fe(SO<inf>4</inf>)<inf>2</inf>·6H<inf>2</inf>O of 0.5 g·L⁻¹, waste molasses of 2.5 g·L⁻¹, Cr(VI) of 100 mg·L⁻¹, pH of 6.0, and with the operational temperature of 45 °C. After 120 h reaction, Cr(total) removal reached 91.10%. The major reduction products [FeS, Cr<inf>2</inf>O<inf>3</inf>, Cr(OH)<inf>3</inf>, S⁰ granules] together with microbes was removed by sludge separation with Cr(VI) in the supernatant (0.027 mg·L⁻¹) being much lower than that (not excess 0.2 mg·L⁻¹) of Electroplating Pollutant Emission Standard.