Traditional and innovative treatment methods for Cr(VI) in soil

Chemistry of Chromium in Soils with Emphasis on Tannery Waste Sites

“…Another cleanup criterion often used for sites is the Toxicity Characteristic Leaching Procedure (TCLP), and the limit for total Cr is 5 mg/L (40 CFR 261.24; as quoted by Higgins et al 1997). This procedure measures leachable Cr concentrations, predominantly Cr(VI).…”

Reduction of hexavalent chromium by Sphaerotilus natans a filamentous micro-organism present in activated sludges

“…Cr(VI) behaves as an oxyanion (CrO 4 2− , Cr 2 O 7 2− ) in water solution, so it cannot be precipitated nor bounded to negatively charged functional groups present in the biomass surface as the carboxylates. Microbial reduction of Cr(VI) to trivalent chromium (Cr(III)) can be applied to remediate contaminated waters where physicochemical methods are costly and produce secondary wastes [8]. Biological reduction of hexavalent chromium is economical, Nomenclature a coefficient (mg Cr(VI) 0 l −1 ) b chromium(VI) reduction coefficient ((mg Cr(VI) 0 ) n (g VSS 0 ) −n h −1 ) Cr(VI) concentration of hexavalent chromium at time t (mg l −1 ) Cr(VI) 0 concentration of hexavalent chromium at time = 0 (mg l −1 ) COD chemical oxygen demand (mg O 2 l −1 ) D 0 ratio between initial Cr(VI) concentration and that of biomass (mg Cr(VI) 0 (g VSS 0 ) −1 ) FR OUR bacterial respiratory activity fraction based on respirometric technique (dimensionless) k coefficient ((g VSS) −n l n h −1 ) k apparent chromium(VI) reduction coefficient (h −1 ) n coefficient (dimensionless) OUR oxygen uptake rate (respirometry) (mg O 2 (l h) −1 ) OUR (control) oxygen uptake rate for control tests (mg O 2 (l h) −1 ) OUR (chromium) oxygen uptake rate for samples treated…”

Reduction of Cr(VI) at a Polyaniline Film: Influence of Film Thickness and Oxidation State

“…Furthermore, the trivalent chromium can be isolated as insoluble chromium(III) hydroxides by adjusting the pH to sufficiently high values, enabling the removal of chromium from the environment. Many of the current chemical (3,4) and electrochemical treatment (5,6) strategies rely on this reduction step. For example, in the chemical treatments, reducing agents are employed while in the electrochemical treatment direct reduction to the trivalent state is achieved through the application of suitable electrode potentials.…”