English abstract
Heavy metals pollution including hexavalent chromium is of great concern due to its high toxicity and carcinogenic effects. Therefore, using cost effective and environmentally friendly technique is a global interest. Microbial bioremediation using fungi is the main point of this research in removing chromium. Aspergillus niger and Trichoderma longibrachiatum were locally isolated from a chromite mining area (wadi Fizh) from a previous study. 7. longibrachiatum showed the highest Cr (VI) removal in which 70.09 % of Cr (VI) was removed from 10 mg/l Cr (VI) solution after 120 hrs. The interdependence of Cr (VI) with Cu (II) was studied since reducing chromium toxicity by fungi will depend on the availability of other heavy metal ions in the aqueous solution, which may directly or indirectly affect the potential ability of different species for bioremediation. Therefore, about 76.58 % of Cr (VI) was removed from solution containing 10 mg/l Cr (VI) and 10 mg/l Cu (II). Cr (VI) removal by T. longibrachiatum was higher in multiple metal solutions at low concentration. Cr (III) oxidation to Cr (VI) by A. niger was found to be 0.6 % compared to T. longibrachiatum (0.49 %) in 10 mg/l Cr (VI). The Eh-pH diagrams showed that all immobilized/mineralized compounds were found to be in the stability field of chromium (III) oxides (Cr2O3) except at higher Cu concentration of 100 mg/l, there is a shift from Cr2O3 to CuCr204. The fungal biomass concentration was higher at low concentration and therefore, more Cr (VI) removal was observed. The specific activity of chromate reductase was found to be 0.02 and 0.08 Unit/mg within 24 and 120 hrs respectively for A. niger. The fungal cells grown in the presence of 200 mg/l Cr (VI) for Aspergillus and Trichoderma sp were examined using SEM and chromium (III) oxide was found (Cr2O3) to be more in diffusible forms, i.e., adsorbed to the cell walls, Although "grainy" precipitate have also been observed.
