Study on remediation and mechanism of immobilized bio-nZVI for chromium (VI) contaminated wastewater in an up-flow bioreactor

This study built an up-flow bioreactor to remediate hexavalent chromium (Cr (VI)) in wastewater. Immobilized bio-nZVI, as the packing of bioreactor, was composed of Cr (VI) resistant bacterium (CRB-B1), nano-zero valent iron (nZVI) and sodium alginate (SA). Response surface analysis (RSA) was used to optimize the best proportion of immobilized bio-nZVI (W-nZVI: VCRB-B1: V-SA = 1: 30: 20, g: ml: ml). Besides, the highest efficiency of Cr (VI) reduction by immobilized bio-nZVI was at 30 celcius, acid condition with initial Cr (VI) concentration of 100 mg/L. Based on the above parameters, the up-flow bioreactor packed with immobilized bio-nZVI was set up. With 1 ml/min of inflow speed and 200 g of immobilized bio-nZVI, Cr could be reduced fast, continuously and completely in bioreactor. The mechanism of Cr (VI) reduction by immobilized bio-nZVI was that CRB-B1 and nZVI both could convert Cr (VI) to Cr (III), meanwhile CRB-B1 was able to promote Fe-0 transport to Fe2+, which enhanced Cr (VI) reduction efficiency of nZVI and the formation of CrxFe1-x(OH)(3). Moreover, nZVI could reduce Cr (VI) at the early stage so as to decrease Cr (VI) resistance on CRB-B1. In conclusion, this study provided an effective method to remediate Cr (VI) contaminated wastewater.