Triple-functional biohybrid for efficient Cr (VI) remediation: Synergistic adsorption, chemoreduction and bioreduction

The reduction and adsorption of Cr(VI) are critical challenges in environmental remediation. In this study, corn straw modified with polyethyleneimine (PEI-CS) was synthesized as carriers to immobilize Bacillus licheniformis MZ1 (PEI-CS-MZ1), enabling simultaneous Cr(VI) reduction and Cr(III) fixation in a high efficiency. Notably, PEI-CS-MZ1 achieved 95.61 % and 81.96 % Cr(VI) reduction under extreme conditions (pH 8 and 11 % salinity), respectively. Furthermore, this composite completely reduced 100 mg/L Cr(VI) within 24 h while maintaining 76.96 % Cr(III) fixation, which was significantly superior to free MZ1 and PEI-CS. PEI-CS-MZ1 also demonstrated exceptional stability, retaining 89.8 % Cr(VI) reduction after 10 operational cycles. This strategy revealed that Cr(VI) reduction and Cr(III) fixation were accomplished via cooperativity of bio-reduction, chemical reduction, chemisorption, and physical adsorption. This work provides theoretical foundations for designing immobilized microbial systems toward efficient remediation of Cr(VI)-contaminated wastewater.