Wastewater treatment using recyclable agar-graphene oxide biocomposite hydrogel in batch and fixed-bed adsorption column: Bench experiments and modeling for the selective removal of organics

Hydrogel biocomposite using graphene oxide and agar biopolymer (agar-GO) was synthesized to treat textile wastewater through fixed-bed adsorption. After characterization, batch experiments were conducted to evaluate the pH effect in the adsorption process, adsorption isotherms, and kinetics for four cationic dyes – Nile Blue A (NB), Methylene Blue (MB), Malachite Green (MG) and Basic Fuchsin (BF). Adsorption equilibrium isotherms were fitted to Freundlich, Langmuir and Sips models, and kinetic data were adjusted to Driving Force models, and Fickian Diffusion equation. Fixed-bed experiments were carried out, and the adsorption capacities on a dry basis were 226.46 mg·g−1 (NB), 79.51 mg·g−1 (MB), 58.25 mg·g−1 (MG), 38.11 mg·g−1 (BF). LDF model was fitted with the experimental breakthrough curves. The column packed with the agar-GO hydrogel was tested for the treatment of synthetic textile wastewater. Color and total organic carbon (TOC) were evaluated and there was an indication of the adsorbent selectivity for the separation of the dyes, which can facilitate dye recovery. Agar-GO proved to be a viable and eco-friendly alternative, since a small amount of material was used to treat over 6 L of wastewater, being most of the composite biodegradable. Moreover, the material exhibited remarkable regenerative capacity, proving its effectiveness for applications in industrial textile wastewater treatment.