Removal of Azo dyes – tartrazine, carmoisine, and allura red – from wastewater using spirulina biomass-immobilized alginate beads: Equilibrium, kinetics, thermodynamics, desorption, and reusability

In the present study, Spirulina microalgae-immobilized alginate beads (Alg-SP) were used as novel adsorbents for the adsorption of tartrazine, carmoisine, and Allura Red azo-dyes from wastewa-ter. Synthesized Alg-SP beads were characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and differential scanning calorimetry analyses. Maximum azo-dye removal percentages were achieved using 100 mg of Alg-SP beads with a ratio of 3.0% (w/v) within 2 h, and tartrazine, carmoisine, and Allura Red removal performances were determined to be 98%, 93%, and 82%, respectively. The adsorp-tion data for azo-dyes onto Alg-SP beads were evaluated by several isotherm equations such as Langmuir, Freundlich, Dubinin–Radushkevich, Temkin, Halsey, and Harkins–Jura isotherm mod-els, but were best described by the Langmuir and Harkins–Jura models as they gave the highest correlation. Pseudo-first-order, pseudo-second-order, Elovich, Weber–Morris, and Bangham models were investigated and dye adsorption onto Alg-SP beads was represented by pseudo-second-order and Elovich kinetic models. After the adsorption process, the beads can easily be regenerated by NaOH and effectively reused over three cycles. Consequently, Spirulina microalgae-immobilized alginate beads have considerable potential for the adsorption of dyes from wastewater.