Uptake and Reduction of Hexavalent Chromium by Aspergillus Niger and Aspergillus Parasiticus

Abstract

The uptake and reduction of Cr(VI) by Aspergillus niger and A. parasiticus was studied in this journal. After 96 hours of growth, the culture solutions spiked with an initial dichromate concentration of 20 mg/l, were completely decolorized and had residual Cr(VI) concentrations of only 0.74 ± 0.55 and 1.69 ± 0.29 mg/l in A. niger and A. parasiticus cultures representing Cr(VI) removal of 96.3% and 91.6%, respectively. In the A. niger culture, significantly (P < 0.01) lower Cr(VI) concentrations were observed within 72 hours of growth compared to those of A. parasiticus, but in both cultures complete removal was almost achieved by 144 hours of growth. The rate of Cr(VI) removal was 0.21 ± 0.09 mgl -1 hr -1 and 0.20 ± 0.07 mgl -1 hr -1 for A. niger and A. parasiticus, respectively. Cellular concentrations of Cr(VI) in the two fungi increased significantly (P < 0.05 -0.001) with increasing concentrations of the dichromate treatments. Although tannic acid as sole source of carbon and energy gave significantly lower Cr(VI) removal than glucose (P < 0.001) and acetate (P < 0.01), it supported the removal of about 85.0% and 68.8% of the metal ion by A. niger and A. parasiticus, respectively. The active mycelia of both fungi showed significantly (P < 0.001) higher Cr(VI) removal than inactivated mycelia after incubation at 30°C for 72 hours. Incubation of cell -free extracts of both fungi with NADH at 30°C for 2 hours showed Cr(VI) reduction of 68.0% and 55.5% for A. niger and A. parasiticus, respectively. These findings suggest that uptake and metabolic reduction may be the process by which the two fungi are able to tolerate the toxic effects of hexavalent chromium. However, Cr removal via uptake by the two fungal biomass was observed to be in the range of 0.5 -1.78% only, for all the concentrations applied, which is insignificant when compared with the initial Cr concentration in the culture medium. The results obtained through this investigation indicate the possibility of treating waste effluents containing hexavalent chromium using Aspergillus niger and A. parasiticus.

Enhanced biological removal of Cr(VI) in Continuous Stirred Tank Reactor (CSTR) using Aspergillus sp.

“…A similar trend has been reported in specific Cr(VI) removal with increase in Cr(VI) concentrations using C. utilis (Muter et al, 2001;Dursan et al, 2003;Shugaba et al, 2012). Further, the removal of Cr(VI) is expected to be occurred initially by bioaccumulation followed by the enzymatic reduction of Cr(VI) into Cr(III) in the media (BorstPaweles, 1981;Gharib and Gadd, 1998;Peña-Castro et al, 2004).…”

Molasses as an efficient low-cost carbon source for biological Cr(VI) removal

“…Two major types of biological Cr(VI) treatment processes exist: suspended growth [25,26] and attached growth [27,28]. Although there are several studies on Cr(VI) reduction in the literature, only a few use attached growth reactors especially under batch operating mode.…”

The Geomicrobiology of Chromium (VI) Pollution: Microbial Diversity and its Bioremediation Potential

“…Biotechnological approaches used to limit the toxicity of metal pollution are achieved by selectively enriching those naturally occurring microorganisms to treat particular toxic wastes. The processes by which microorganisms influence removal and recovery of the toxic metals are: biosorption (passive uptake of metal without reduction), bioaccumulation (active uptake without reduction), and biotransformation by enzymatic reduction [52,53]. Chromium (III) is approximately one thousand-times less toxic than chromium (VI), because the cell membrane is almost impermeable to Cr (III) [54].…”