Removal and recovery of heavy metals through size enhanced ultrafiltration using chitosan derivatives and optimization with response surface modeling Edward Kavitha, Appunni Sowmya, Sivaraman Prabhakar, Prince Jain, Rahul Surya, Mathur P. Rajesh ⁎ Department of Chemical Engineering, SRM Institute of Science and Technology, Chennai 603 203, India abstract article info Article history: Received 22 January 2019 Received in revised form 15 February 2019 Accepted 19 March 2019 Available online 30 March 2019 N‑N‑N‑triethylammonium chitosan (TEAC) and carboxymethyl chitosan (CMCh), the two water-soluble chitosan derivatives were utilized for the removal and recovery of heavy metals by size enhanced ultrafiltration (SEUF). The strong positive quaternary ammonium [–N + (C 2 H 5 ) 3 ] cation in TEAC interacts with Cr(VI), which exists as a strong chromate anion thereby enabling the efficient removal of chromate through ultrafiltration. CMCh con- sists of \\ COOH and \\ NH 2 moieties, which facilitate interactions with heavy metals such as Cu(II) and Ni(II). FTIR, SEM, and EDAX were used to characterize the chitosan derivatives before and after the removal of metals. The experiments were designed with the central composite design (CCD) of response surface methodology (RSM). The metal ion removal experiments were conducted as per the statistical design to determine the optimum process conditions; initial pH of the feed solution, polymer to metal loading ratio (P/M), and initial concentration of the feed solution. The optimization study was conducted to maximize the heavy metal rejection and binding capacity of the chitosan derivatives. The analysis of variance (ANOVA) was performed to validate the developed regression models. © 2019 Published by Elsevier B.V. Keywords: Size enhanced ultrafiltration Heavy metals Quaternary ammonium chitosan Carboxymethyl chitosan RSM 1. Introduction Recovery of heavy metals is vital for recovering the metal and preventing its adverse effect on the environment. The main heavy metals present in industrial wastewater are Cu(II), Ni(II) and Cr(VI). Copper and nickel find applications in electroplating, paint, metal finishing, and mining industries. Chromium salts are used widely in in- dustries such as leather, electroplating, and textile. Cr(III) is an essential trace element for human beings, while the detrimental effects are due to carcinogenic Cr(VI). According to World Health Organization (WHO) and Bureau of Indian Standards (BIS), the tolerance limits for copper, nickel and chromium in drinking water are 0.05, 0.01 and 0.05 mg/L respectively [1–3]. An investigation by Ministry of Water Resources, India in 2012 [4] at 387 water quality monitoring stations located on Indian rivers, a total of 21 samples from 11 major Indian rivers were found to have chromium concentration exceeding the tolerance limit of 0.05 mg/L. The maximum concentration of chromium found in the above study was 0.36 mg/L. In the study, 68 samples were found to have copper concentrations above the acceptable limits, and the maximum copper concentration observed was 0.18 mg/L. The nickel concentration in 107 water samples was also more than the prescribed limits with the maximum at 0.08 mg/L. Hence, there is an unmet need for the efficient remediation process to reduce the heavy metals levels in effluent water. Adsorption, chemical precipitation, membrane process, and chemical/ photocatalytic reduction are the conventional techniques utilized for heavy metal removal. Among these techniques, adsorption appears as a facile method for the removal and recovery of heavy metals, but the contact duration required for the process is relatively high. Size enhanced ultrafiltration (SEUF) is an alternative approach to adsorptive removal because (i) all the functional groups in the ligands can be utilized (ii) the contact duration required is relatively less and (iii) large volume can be treated within a short duration of time [5]. In size enhanced ultra- filtration, water-soluble polymers such as polyethyleneimine [6–9], carboxymethyl cellulose [10], sodium polyacrylate [11], polyvinyl alcohol [12], polyacrylic acid-co-maleic acid [13] are some of the reported complexing agents. Polyethyleneimine is extensively used for heavy metal removal because of the wide availability of \\ NH \\ for chelation. Bulk molecules such as EDTA [14], hexadecyl pyridine chloride [15], etc., and surfactants such as sodium dodecyl sulphate, dodecylbenzene sulfonic acid, dodecylamine [16,17], etc., have also been attempted with SEUF. Chitosan is an abundantly available biopolymer with a primary amine in its chemical structure and likely to impart good metal binding ability. Different derivatives of chitosan with metal binding capacity International Journal of Biological Macromolecules 132 (2019) 278–288 ⁎ Corresponding author. E-mail address: mprajesh@gmail.com (M.P. Rajesh). https://doi.org/10.1016/j.ijbiomac.2019.03.128 0141-8130/© 2019 Published by Elsevier B.V. Contents lists available at ScienceDirect International Journal of Biological Macromolecules journal homepage: http://www.elsevier.com/locate/ijbiomac