Bioremediation of hexavalent chromium Cr (VI) in fluoride contaminated environment by novel bacteria Bacillus albus SSAU-9.

Cr (VI) is highly toxic, persistent, and non-biodegradable in soil-water systems, while fluoride levels in many aquatic environments are rising to similarly hazardous concentrations. This study investigates the capacity of Bacillus albus strain SSAU-9, isolated from the River Ganges and identified by 16S rRNA gene sequencing- to remove Cr (VI) in both the absence and presence of fluoride. Several parameters (inoculum size, salinity, pH, external electron donor, and initial Cr (VI) and fluoride concentrations) were optimized to maximize removal efficiency. Surface morphological changes were visualized by scanning electron microscopy (SEM), and functional groups involved in adsorption-reduction were identified via FTIR spectroscopy. Kinetic analysis showed that Cr (VI) reduction followed a pseudo-second order model; the Webber-Morris intraparticle diffusion model further described mass-transfer control at 50 ppm Cr (VI) only. The Langmuir and Redlich-Peterson isotherm models provided the best fit to the experimental data, indicating monolayer adsorption behaviour. The Dubinin- Radushkevich (D-R) isotherm also showed a good fit, but only in the absence of fluoride. Phytotoxicity assays with mustard (Brassica juncea) seeds demonstrated that treated effluents were non-inhibitory, confirming the biosafety of the process. These results highlight the Bacillus albus (SSAU9) as an efficient, environment friendly agent for Cr (VI) detoxification even under fluoride co-contamination, offering a practical bioremediation strategy for mixed-pollutant systems.