Feasibility and mechanism of microbial-phosphorus minerals-alginate immobilized particles in bioreduction of hexavalent chromium and synchronous removal of trivalent chromium

Chromium(VI) contaminated groundwater has become an increasingly prominent problem due to its extensive application in industry. Based on the easy-loss defect of microbial in practical application and previous research on the coupling enhancement of Cr(VI) bioreduction by phosphorus minerals, Microbial-Phosphorus minerals-Alginate (MPA) immobilized particles were proposed and investigated in this study. The feasibility of MPA immobilized particles were proved, with the higher reduction efficiency, lower phosphorus surplus, significant 94% of total Cr reduction and 85% of intragranular fixation. These superiorities were also obtained at different pH and initial Cr(VI) concentration conditions. Furthermore, the mechanisms of the enhancement of MPA were investigated from microbial level (microbial biomass, antioxidase, gene expression and microbial community analysis) and physics level (adsorption kinetic and isotherm), where the speculation that the reduction mainly took place outside the particles was proposed. This research provides a new approach for the practical application of Cr(VI)-contaminated groundwater in-situ bioremediation.