Bioremediation of Cr(VI) using bacterial biofilms supported on rice husk: A sustainable agroresidue-based bioprocess

Abstract In search of a Cr(VI) removal bioprocess, within a circular economy perspective, we combined two autochthonous bacterial consortia obtained from industrial residues and an agricultural waste (rice husk of Oryza sativa). After characterizing the rice husk (rh) properties, the bacterial growth and biofilm formation, we studied the taxonomical profile of the bacterial consortia (C55, C33, and C21, the last is a combination 2:1 of the previous ones). By using SEM analysis, we confirmed the presence of a smooth layer of exopolysaccharides (EPS) over the rice husk surface. Total bacterial biodiversity, assessed through MiSeq analysis, showed that the addition of Cr(VI) stimulated the growth of two main populations ( Cellulosimicrobium and Siminovitchia ) while inhibiting Peptoniphilus , Cutibacterium and Rhodococcus . We also evaluated chromium depletion, in batch experiments, with particular emphasis on its sorption to the agroresidue and its biotransformation by the biomass. When exposed to 200 mg.L -1 Cr(VI), the system containing both rh and the bacterial consortium completely removed Cr(VI) from the effluent with half-times between 53 and 67 h. The combination of Cr(VI) biosorption by rh and its biotransformation to Cr(III) by bacterial consortia confirmed an effective synergy capable of removing 92% of Cr(VI). This work supports the potential of an innovative bioprocess based on bacterial biofilms grown on rh for the mitigation of Cr(VI) contamination.