Biological Reduction of Hexavalent Chromium--A Field Study.

When ferrochromium is produced at Vargön Alloys AB (Vargön, Sweden), an offgas dust is generated as a byproduct. A leachate that contains hexavalent chromium (Cr⁶⁺) is formed when rainwater percolates through the dust deposit. In this study, Cr⁶⁺ in the leachate was reduced to trivalent chromium (Cr³⁺) by biological treatment in a biofilm process operated under anaerobic conditions. The reactor volume was 26 m³ and it was filled with 16 m³ plastic packing. Acetic acid was added as an electron donor. The Cr⁶⁺ was reduced from 10 to 20 mg/L to below 0.03 mg/L when the reactor was operated at a hydraulic retention time of 11 hours. The reduction activity in the process gradually decreased as the water temperature dropped below 10°C. [ABSTRACT FROM AUTHOR]