Response surface methodology and optimization of arsenic continuous sorption process from contaminated water using chitosan

Abstract

Arsenic presence in water implies a serious social problem in many countries. Among the different water remediation techniques, continuous sorption in columns is a useful methodology because of its effectiveness and low cost. Arsenic sorption onto the natural, non-toxic and biodegradable biopolymer chitosan has been studied. In this work, a green, sensitive and economic method was adapted to dose As(V) concentrations. Kinetic and equilibrium studies were carried out. Furthermore, a continuous sorption process was applied and improved by a Response Surface Methodology (RSM) - Central Composite Design (CCD). Column bed height and feed flow rate were selected as independent variables, while the percentage of As(V) removal was considered as the response to be optimized. With the aim of predicting the highest elimination efficiency of arsenic, a second-order polynomial regression model was used. Results showed that As(V) batch sorption appears to be completed after 5 min with a 19.63 mg g−1 of maximum sorption capacity (25 °C, pH 4.5). Equilibrium and kinetic sorption studies followed Langmuir and pseudo-first order models, respectively. Free energy (7.10 kJ mol−1) obtained with Dubinin-Radushkevich model (D–R), demonstrated that the remediation process was physical sorption. The As(V) retention by chitosan was confirmed using FT-IR and XRD spectroscopy techniques. In optimal conditions, a maximum of 76.8% was obtained for As(V) continuous elimination. Thomas and Modified Dose-Response demonstrate to be the best fitting models for continuous sorption data. A critical bed depth, was determined to be 1.5 cm, applying the Bed Depth Service Time model (BDST).