Toxicity and Microbial Bioremediation of Chromium Contaminated Effluents

Chromium is one of the most toxic heavy metals, found in environment in two stable forms (trivalent and hexavalent chromium) being released into water by various industrial activities. Both forms of chromium have negative effects on human health, but the hexavalent form is the one considered extremely toxic for all living organisms. In 2017, at the European level, considering surface waters, the energy sector, waste and wastewater management, and others activities, were released about 834 tons of chromium. In order to reduce the chromium concentrations in the effluents discharged by industrial activities, different processes can be applied, including biosorption and bioaccumulation processes. The chromium ions are removed by microorganisms from aqueous solutions by various mechanisms (e.g. ion exchange, complexation, chelation, precipitation, electrostatic attraction, adsorption on the cell wall surface) including extraand intra-cellular reduction of Cr
⁶⁺
to Cr
³⁺
.