Optimisation of Aspergilus flavus-Mediated Biosorption Process for Removal of Cr (VI) and Mn (II) Ions by Response Surface Methodology Approach

In this study, soil samples from textile industries located in the Arba Minch region were collected and screened for the presence of heavy-metal-resistant fungi. Among the three isolates identified during the screening process, Aspergillus flavus exhibited the highest resistance to heavy metals such as Cr (VI) and Mn (II). Our results showed that A. flavus biosorbed Mn and Cr at concentrations of 80.5% and 68.4%, respectively, making it a promising biosorbing agent. Furthermore, our study demonstrated that pretreatment of A. flavus fungal biomass with NaOH enhanced the biosorption of Mn and Cr. To optimize the biosorption process, a study was conducted using A. flavus biomass with three independent variables: pH (2–10), biomass dosage (1–5 g/mL), and contact time (40–150 min). The Box-Behnken experimental design was used to determine the optimal biosorption values. Maximum biosorption was achieved at pH 10, biomass dosage (5 g/mL), and contact time of 150 min. These conditions resulted in 88 and 80.29% sorption efficiency for manganese and chromium ions, respectively, by A. flavus biomass. The scanning electron microscopic analysis of A. flavus biomass indicated the presence of large porosities on the microbial surface due to NaOH treatment, which assisted in the higher sorption of heavy metals.