Low-cost biosorption of Methylene Blue and Congo Red from single and binary systems usingSargassum latifoliumbiorefinery waste/wastepaper xerogel: an optimization and modeling study

There is a growing interest for the utilization of brown macroalgae for integrated production of various value-added products with zero waste generation. Therefore, the biorefinery waste ofSargassum latifoliumafter the sequential extraction of polyphenols, fucoidan, and alginate was utilized for the preparation of an environmentally benign xerogel using wastepaper. The adsorption efficiency of the xerogel for Methylene Blue (MB) and Congo Red (CR) was successfully evaluated using Box-Behnken experimental design. Under the optimized conditions, the maximum MB removal was 92.54% compared with 94.97% for CR for the single system and for the binary system the maximum bioremoval was 97.16% and 87.66% for MB and CR, respectively. The maximum dye adsorption (q(e)) for MB and CR in a single system was 8.54 mg g(-1)and 20.97 mg g(-1)at pH 5.0, respectively, while theq(e)was reduced in the binary system due to antagonistic interaction. The kinetics of MB and CR biosorption from single and binary systems were better represented by the pseudo-second order model. The adsorption mechanism was predominantly intraparticle diffusion, but the effect of the external mass transfer was significant. Langmuir, Freundlich, Langmuir-Freundlich, and Temkin isotherms were able to represent the experimental data, but they differ in priority depending on dye type and pH. The thermodynamic analysis indicated that the adsorption process was endothermic, except MB in a single system. The developed xerogel is an environmentally benign biosorbent suitable for cationic and anionic dye removal from single or multicomponent dye containing effluents.