BIOLOGICAL Cr(VI) REDUCTION

Scientific interest on chromium removal from water and wastewater has escalated recently. Chromium compounds exist in the environment naturally but are mostly found due to anthropogenic activities (tanning, paint, cement industries, etc.). Hexavalent chromium [Cr(VI)] is of major environmental importance because it is one of the most stable chromium forms found in the environment. It is soluble, highly toxic, carcinogenic and mutagenic. Conventional methods of Cr(VI) treatment are mainly physicochemical, such as ion exchange, filtration, precipitation, electrochemical treatment, chemical reduction and adsorption. However, these methods have significant drawbacks such as the production of toxic sludge or other secondary products which require further processing. Therefore, an environmentally friendly, low-cost treatment method should be developed. The use of microorganisms has received much attention in recent years since they carry a wide range of binding sites for heavy metal ions. Advances in the fields of environmental microbiology and biotechnology indicate that bacteria, fungi, yeast and algae, either as pure or mixed cultures, can remove Cr(VI) from aqueous solutions under aerobic and/or anaerobic conditions. Cr(VI) reduction is significantly affected by various process parameters such as initial Cr(VI) concentration, carbon source, inoculum volume and age, initial pH, and incubation temperature.