Biosorption of trivalent chromium from a model tanning solution by adapted aspergillus niger

Abstract

Industrial effluents containing metallic species are responsible for environmental degradation which have been prioritised as major inorganic contaminants. Conventional methods are quite expensive resulting in need for cost-effective process for removing heavy metals from discharging effluents. The use of microbial biomass for removal of heavy metals from aqueous solutions (biosorption) is one such approach gaining increasing attention. Trivalent chromium ion present in tannery effluents has been the targeted ionic species for removal due to its exceeding limits in industrial discharges (<--0.3 ppm as per WHO). At NML, efforts were made for biosorption of trivalent chromium from tannery effluents with Cr (III) concentration in the range 1500-5000ppm. Aspergillus niger, obtained from a culture bank has been used in biosorption of trivalent chromium of tannery effluents. The fungal species grown in Czapek Dox Medium and adapted on Cr(III) ions ranging from 10-2000ppm at 2.5 pH and 35°C, was used for biosorption of chromium from a model tanning solution. A.niger was used in forms such as live, adapted and pre-treated (autoclaved, alkali-treated) for biosorption at pH 2.5 and 35°C. At Cr(IlI) conc. of 2000ppm in the aqueous solution, the adsorption efficiency followed the order: alkali treated (52%)>live(38%)>autoclaved dead mass(27%). The varying biosorption capacities may be attributed to exposed metal binding sites in alkali treated fungus causing high biosorption efficiency which also obeyed the sorption isotherm.