The Research On The Removal Of Hexavalent Chromium By Fe Combined With Microbial Reduction

Removal of Cr(VI) from wastewater by iron and microorganism was studied. Two reduction systems were established to investigate the impacts and mechanisms of Cr(VI) reduction by iron and microorganism.Effects of temperature, initial pH, carbon source, glucose addtion, Fe(III) concentration, and chelating agent on Cr(VI) removal were investigated. Results indicated that the optimal temperature for Cr(VI) reduction was32℃and the optimal pH was5.8. Carbon source was required for Cr(VI) reduction, and glucose was chosen as the most suitable electron donor. Amendments with Fe(Ⅲ) and citric-3Na enhanced the reduction of Cr(VI), while the addition of EDTA-2Na inhibited the process.Effects of temperature, initial pH, scrap iron loading, inoculum size, initial concentration of Cr(VI), and other ions on Cr(VI) removal were investigated. Results revealed a promotion of Cr(VI) reduction by scrap iron in the presence of microorganism. The highest efficiency of reduction was observed when pH was5.8and temperature was42℃. The efficiency of Cr(VI) reduction was increased with increasing amount of scrap irons and mircrooranisms, and was decreased with increasing initial concentration of Cr(VI). Mn2+、Zn2+、Co2+、Cu2+and Ni2+ions could cause varying degrees of inhibition to Cr(VI) reduction in the order of Ni2+> Cu2+> Co2+> Zn2+> Mn2+. System consisting of scrap iron and microorganism could complete three rounds of Cr(VI) reduction within a gradually longer time.The mechanisms of Cr(VI) removal by iron and microorganism were analyzed in detail. Analysis showed that Cr(VI) removal by microorganism in the presence of Fe(III) was completed through two mechanisms, including direct reduction by microorganism and indirect reduction by bio-reduced Fe(II). Soluble Fe(III) enhanced Cr(VI) reduction by microorganism by shuttling electrons from bio-reduced Fe(II) to Cr(VI) in a coupled biotic-abiotic cycle and hence, Cr(VI) was reduced to Cr(III) followed by deposition to sludge. Cr(VI) removal by scrap iron and microorganism was completed through three ways, which were redution by Fe0, direct reduction by microorganism and indirect reduction by bio-reduced Fe(II). Characterizations with XPS indicated the deposition of Cr element on scrap iron surface in the forms of Cr(III) and Cr(VI), and Cr(III) was most likely to be in the forms of Cr(OH)3and FexCr1-x(OH)3.