Aloe vera mucilage as a sustainable biopolymer flocculant for efficient arsenate anion removal from water†

Abstract

In recent years, utilization of biopolymers as natural coagulant–flocculant (CF) systems has become an area of interest, due to their sustainable nature (renewable, biodegradable, and non-toxic) and potential utility as alternative systems to replace synthetic flocculants. Herein, a biopolymer extracted from Aloe vera mucilage (AVM) was investigated for its arsenic(V) removal properties in a CF water treatment process. Structural characterization of AVM was supported by spectroscopy (FTIR, ¹³C solids NMR & XPS), TGA, rheology, and pH_pzc. The arsenic(V) removal process was optimized by employing the Box–Behnken design under three main factors (coagulant, flocculant dosage and initial arsenic(V) concentration), which led to a reduction of the initial arsenic(V) concentration to levels below the Maximum Acceptable Concentration (MAC; 10 μg L⁻¹). The kinetics and thermodynamics of arsenic(V) removal were analyzed with a one-pot in situ method, where the kinetic profiles followed a pseudo-first-order model. The thermodynamic parameters are characteristic of a spontaneous (entropy-driven) and endothermic physisorption removal process. Flocs isolated from the process were analyzed by XPS, where the results reveal that calcium and amide groups of AVM contribute to the arsenic(V) removal mechanism.