Remediation options for the treatment of electroplating and leather tanning effluent containing chromium - A review

Chromium used in the electro plating and tanning industries causes environmental pollution through the generation of effluent. Various methods such as precipitation-flocculation coupled with pre/postoxidation, reduction, and concentration are often employed to control environmental pollution. Though these techniques, referred to as "removal-disposal,'' serve the purpose of satisfying water pollution norms, they produce solid residues containing Cr(OH)(3) as the sludges, which are usually dumped as landfill. Besides the possibility of mobility of the metal as Cr(VI) by the biological and chemical oxidation, the dumping of sludges also leads to the loss of metal values exerting pressure on the corresponding primary reserves. Therefore, processes based on "recovery-reuse'' are now being increasingly projected and used. In this article, streams/wastes containing chromium relevant to electroplating have been identified and the applicability of conventional and promising techniques to treat such substances have been reviewed. Earlier developments and recent modifications on the most common routes, such as precipitation, evaporation, bioremediation, etc., are highlighted. Other methods such as electrolysis, solvent extraction, membrane separation, ion exchange, etc. are discussed with respect to their applicability, status, and scope.