Transportation and distribution of chromium in the anaerobic sludge treating the chromium-containing wastewater

The chromium distribution and transportation in the anaerobic activated sludge was investigated using a sequential extraction method. The results showed that Cr(VI) in aqueous solution was reduced by the metabolic product of SRB and form indissoluble Cr(OH)(3) in a solid phase. More than 99% of Cr(III) in the sludge was in a stable residual form (RES) of bio-reduction. The Cr(VI) was mainly present in RES and organic form (OR). With increasing Cr(VI) concentration, Cr(VI) was transferred from RES into OR and even exchangeable form (EXCH). Meanwhile, sulphate and co-existing metal ions affected the occurrence form of Cr(VI).