Cr(VI) removal and mechanism from simulated polluted groundwater by Klebsiella variicola H12-CMC-FeS@biochar assisted permeable reactive barrier

Abstract

Permeable reactive barrier(PRB) is an attractive technique for in situ polluted groundwater remediation. Klebsiella variicola H12-Carboxymethylcellulose -FeS@biochar (K.variicola H12-CMC-FeS@biochar) was used as filling medium in PRB to remove chromium contamination from simulated groundwater. The results showed that the chromium removal efficiency was 94 %, which was more effective than k. variicola H12 or biochar respectively and the optimal solid-liquid ratio was 30:1. Ionic strength and initial chromium concentration in groundwater have greater influence on the treatment effect. Scanning electron microscopy(SEM) and fluorescence microscopy showed that biofilm covered on the surface of the material. X-ray Photoelectron Spectroscopy(XPS) indicated that most of hexavalent chromium(Cr(VI)) and trivalent chromium(Cr(III)) were adsorbed by k. variicola H12-CMC-FeS@biochar. Cr(III) originated from the reduction of chromium by K. variicola. Furthermore, quantitative real-time polymerase chain reaction(qPCR) results showed that the expression level of ChrA, ChrB and ChrR genes increased, which contributed to relieve cytotoxicity. These changes improved the resistance of k. variicola H12 to Cr(VI), promoting Cr(VI) reduction. In summary, biofilm adsorption and microbe reduction were the two primary ways to enhance the chromium removal efficiency. It provided a new method for treating in-situ groundwater pollution by PRB technology using biochemical materials as mediums.