The Cr(VI) bioremediation potential of Chlamydomonas debaryana

Abstract

Chromium (Cr) is an essential industrial component and has many applications in industrial manufacturing. Anthropogenic activities can lead to the release of hexavalent chromium [Cr(VI)] as well as trivalent chromium [Cr(III)]. Cr(VI) is 1,000 times more toxic than Cr(III), and very detrimental to most organisms even at low concentrations. Chlamydomonas debaryana, a freshwater algae, appeared to be Cr(VI) resistant and was able to survive in Cr(VI) concentrations of up to 80 mg/L for an extended period in packed aquifer media columns. This micro-green algae strain was isolated alongside Cr(VI) reducing bacteria (CRB) at a Cr(VI) contaminated site in South Africa. In this study, the growth response of C. debaryana in the presence of Cr(VI) was compared to that of Chlamydomonas reinhardtii, to assess the Cr(VI) tolerance of C. debaryana. At 50 mg/L Cr(VI) concentration the maximum chlorophyll a increase was 25.3 % for C. debaryana and 34.2 % for C. reinhardtii. However, after 3.5 d the chlorophyll a content decreased only 38.1 % for C. debaryana compared to a 100% decrease for C. reinhardtii. Indicating that C. debaryana is only slightly more resistant than C. reinhardtii. Zero Cr(VI) removal was observed with the algae: C. debaryana could not reduce Cr(VI) to Cr(III) or adsorb Cr(VI) anions from the solution. C. debaryana as well as C. reinhardtii, algae cells are inhibited when directly exposed to Cr(VI) in continuously mixed batch reactors. C. debaryana might be better suited to use in cooperation with CRB for Cr(VI) treatment in a biofilm reactor. This research can lead to an improved treatment set up for Cr(VI) pollution that requires fewer chemical and energy inputs and produces less secondary waste.