3-level Box–Behnkenoptimization of hexavalent chromium reduction by chromate resistant Trichoderma asperellum cells from simulated and industrial effluent

Hexavalent chromium tolerant non-pathogenic fungi isolated from lab waste were used for the reduction of toxic Cr(VI) (hexavalent chromium) from simulated and tannery effluent. The fungal cells were identified as Trichoderma asperellum (T. asperellum) through genomic DNA sequencing. Surface morphology of the cells and the functional groups embedded on their cells were studied using Scanning Electron Microscopy (SEM) and Fourier Transform infrared spectroscopy (FT-IR). The minimum inhibitory Cr(VI) concentration that the cells can tolerate was determined to be 11.53 mM. The effect of batch parameters influencing Cr(VI) reduction was numerically optimized by three parameter Box–Behnken response surface model (RSM) to evaluate two responses, Cr(VI) removal percentage and residual Cr(VI) concentration. The optimized process parameters for a maximum Cr(VI) removal of 86.73% and residual Cr(VI) concentration of 0.2013 mM were found to be pH 3.29, temperature 301 K and an initial Cr(VI) concentration of 1.33 mM. Crude extracellular and intracellular enzymes have been isolated and their activities over Cr(VI) reduction were determined as 0.0582 mM min⁻¹ mL⁻¹ and 0.0135 mM min⁻¹ mL⁻¹ respectively. Michelis–Menten parameters (V_max and Km) of the enzymatic Cr(VI) reduction were depicted as 0.0015 mM s⁻¹ and 13.11 mM respectively. Tannery effluent containing an initial Cr(VI) concentration of 1.023 mM was reduced to 0.446 mM with the cells at optimum conditions. The results showed that free T. asperellum cells can be utilized for detoxification of simulated and real Cr(VI) containing aqueous solutions.