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Background: The contamination by heavy metals, particularly hexavalent chromium Cr (VI), is a pressing environmental concern. Cr(VI) is highly toxic, non-biodegradable and carcinogenic. Traditional remediation methods are often costly, energy-intensive, or generate secondary waste. This study explores the optimal conditions for the bacterium Bacillus subtilis in reducing Cr(VI) from synthetic wastewater.
Results: The research employed batch experiments to simulate wastewater treatment. The removal of Cr(VI) was measured spectrophotometrically. The active functional groups were studied using Fourier Transform Infrared Spectroscopy that showed an incremental shift for alkyl halides (500.75 cm−1) and OH-groups (3347 cm−1) were observed. Scanning Electron Microscopy images demonstrated that the surface morphology of the biosorbent was more homogenous before than after adsorption. The biosorbent’s structure was confirmed by a prominent peak in X-ray Diffraction at 290.04°. The highest adsorption was observed at the adsorbent dose of 0.5 g/L, the contact time 60 min, pH 6 and temperature of 40°C. The thermodynamic parameters validated the process’s feasibility and spontaneity. Several models for biosorption kinetics and isotherm were tested. The pseudo-second-order was more suitable than the pseudo-first-order model. Langmuir isotherm model had the best fit compared to Freundlich, Dubinin–Radushkevich, and Temkin models.
Conclusions: B. subtilis appeared to be resistant to chromium and reduce Cr(VI) efficiently. This study shows the potential of B. subtilis as a viable bioremediation agent for Cr(VI) contamination in wastewater and should be studied further using real wastewater with different pollutants.
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