Response Surface Modeling for Co-Remediation of Cr⁶⁺ and Pentachlorophenol by Bacillus cereus RMLAU1: Bioreactor Trial and Structural and Functional Characterization by SEM-EDS and FT-IR Analyses

ABSTRACT

This is the first report on optimization of process variables for simultaneous bioremediation of pentachlorophenol (PCP) and Cr⁶⁺ employing traditional and response surface methodology (RSM). In a one-factor-at-a-time approach, the effect of PCP level exhibited maximum bacterial growth and Cr⁶⁺ (82%) and PCP (91.5%) removal at initial 100 mg PCP L⁻¹ with simultaneous presence of 200 mg Cr⁶⁺ L⁻¹ within a 36-h incubation. However, at varied Cr⁶⁺ concentrations, maximum growth and Cr⁶⁺ (97%) and higher PCP (59%) removal were achieved at 50 mg Cr⁶⁺ L⁻¹ with simultaneous presence of 500 mg PCP L⁻¹ within a 36-h incubation. The Box-Behnken design suggested 100% Cr⁶⁺ and 95% PCP remediation at 36 h under optimum conditions of 75 mg PCP and 160 mg Cr⁶⁺ L⁻¹, pH 7.0, and 35°C; Cr⁶⁺ removal was further enhanced to 97% in bioreactor trial. Fourier transform infrared (FT-IR) analysis revealed the likely involvement of hydroxyl, amide, and phosphate groups in Cr³⁺ binding. Scanning electron microscopy and energy-dispersive x-ray spectroscopy (SEM-EDS) showed biosorption of reduced chromium on bacterial cell surface. This isolate can be employed for eco-friendly and effective in situ bioremediation of Cr⁶⁺ and PCP simultaneously.

KEYWORDS:

• bioremediation
• chromium
• FT-IR
• pentachlorophenol
• RSM
• SEM-EDS