Batch adsorption and process optimization for sequestration of Cr(VI) from aqueous solution using biofilm forming filamentous fungus Aspergillus niger BSC-1

Chromium (Cr) contamination in an aquatic environment is one of the greatest concerns nowadays. However, biosorption by various microorganisms is proven to be an environmentally sustainable method. The present study investigated fungal biofilm-mediated sorption of hexavalent chromium [Cr(VI)] using manglicolous fila-mentous fungus Aspergillus niger BSC-1 obtained from the Indian Sundarban mangrove ecosystem. Biosorbents, such as fungal pellet and fungal biofilm, were utilized for Cr(VI) sequestration. The result showed significantly higher removal of Cr(VI) by fungal biofilm (97.81 +/- 2.5 %) than the fungal pellet (79.14 +/- 2.4 %) (P < 0.05; two-way ANOVA). Batch adsorption study showed that the highest removal efficiency was attained at 40 degrees C and pH 3 with 3 g/L of fungal biofilm. The adsorption isotherms, kinetics and thermodynamic analysis suggested monolayer, endothermic and chemisorption of Cr(VI) on the fungal biofilm biosorbent. The adsorption process was further optimized using response surface methodology (RSM) -Central Composite Design (CCD), suggesting the quadratic model for Cr adsorption with high significance (P < 0.0001). The 3D surface plots among the three key variables, i.e., pH, temperature and Cr concentration, revealed that maximum sequestration (92.39 %) was achieved at 40 degrees C, pH 3 and 30 mg/L of Cr(VI) using 3 g/L of fungal biofilm. Regeneration study demonstrated that fungal biofilm retained 87.19 +/- 3.23 % of Cr(VI) sorption with no significant reduction in Cr(VI) removal after five successive adsorption-desorption cycles. X-ray photoelectron spectroscopic analysis showed that adsorption, reduction and complexation mechanisms were involved in Cr(VI) detoxification. Furthermore, the fungal biofilm biosorbent efficiently removed approximately 100 % of Cr(VI) from leather effluent within 90 min of reaction time.

Automated summary

This study found that the manglicolous filamentous fungus Aspergillus niger BSC-1 from the Indian Sundarban mangrove ecosystem can effectively sorb hexavalent chromium (Cr(VI)) in aquatic environments. The fungal biofilm showed significantly higher removal of Cr(VI) compared to the fungal pellet. The optimal adsorption conditions were found to be 40 degrees C and pH 3, using 3 g/L of fungal biofilm. The adsorption process followed monolayer, endothermic, and chemisorption characteristics. The fungal biofilm retained its adsorption capacity for Cr(VI) after multiple adsorption-desorption cycles and was also effective in removing Cr(VI) from leather effluent.