Cr(VI) removal using the combination of the Cr(VI)-resistant and Cr(VI)-reducing biofilm and the alum-polyacrylamide

Abstract

This paper describes the removal of Cr(VI) using the combination of bacterial reduction of Cr(VI) to Cr(III) by wood husk–packed column containing the Cr(VI)-reducing biofilm followed by Cr(III) removal using the coagulation-flocculation technique. The chromium removal process was carried out at the laboratory-scale for 90 days using different batches of Cr(VI) ranging from 35 to 231 mg L−1. Analysis of variance (ANOVA) showed a high coefficient of determination (R2) value of 0.9941, thus ensuring a satisfactory adjustment of the second-order regression model with the experimental data. The experimental observations were in reasonable agreement with the modeled values. The biofilm was able to completely reduce 100 mg L−1 Cr(VI) in 6 h while a longer contact time (18 h) was needed for higher Cr(VI) concentrations. In this study, ORP (oxidation-reduction potential) was used as the control parameter during the Cr(VI) reduction process. The coagulation/flocculation process using the combination of alum and polyacrylamide results in complete removal of color, 85% Cr(III), and 97% turbidity. The field emission scanning electron microscope (FESEM) analysis of the biofilm revealed the embedding of bacterial cells in extracellular polymeric substances (EPS). This study successfully demonstrated the potential application of a bacterial biofilm and chemical systems to remove chromium contamination from water systems.