Cr(VI) Removal Using the Combination of the Cr(VI)-Resistant and Cr(VI)-Reducing Biofilm and the Alum-Polyacrylamide
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Cr(VI) Removal Using the Combination of the Cr(VI)-Resistant and Cr(VI)-Reducing Biofilm and the Alum-Polyacrylamide Zainul Akmar Zakaria
&
Wan Azlina Ahmad
Received: 1 May 2020 / Accepted: 14 September 2020 # Springer Nature Switzerland AG 2020
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 laboratoryscale 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
Z. A. Zakaria School of Chemical and Energy Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia W. A. Ahmad (*) Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia e-mail: [email protected]
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. Keywords Biofilm . Coagulation . Chromium . Acinetobacter . Resistant . Polyacrylamide
1 Introduction Hexavalent chromium Cr(VI) contamination in the environment is a result of extensive usage of chromate and dichromate in numerous industries including electroplating, stainless steel, and pigments. Conventional methods to remove chromate species from industrial wastewaters include chemical reduction using sodium metabisulfite, followed by Ca(OH)2-induced precipitation. Chromate (CrO42−) is the prevalent species of Cr(VI) in natural aqueous environments and is the major pollutant from chromium-related industries (Yao et al. 2020). Of late, the use of high-performance bioreactors, packed with immobilized microorganisms, to reduce chromates to the less soluble trivalent chromium species has been gaining attention (Bandara et al. 2020). Microorganisms would be embedded in an extracellular polymeric substances (EPS) matrix composed of polysaccharides, proteins, and nucleic acids. EPS provide protection to biofilm cells by providing a diffusive barrier to any toxi
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