Studies on dye biosorption enhancement by chemically modified Fucus vesiculosus, Spirulina maxima and Chlorella pyrenoidosa algae

Dyes and pigments are used in a plethora of industrial segments, producing a significant effluent amount containing these compounds. Faced with increasingly restrictive regulations on effluent discharges, it becomes necessary to propose more effective and low-cost alternatives to the conventional chemical, physical and biological treatments. The present study evaluated three algae species, Fucus vesiculosus (F. vesiculosus), Spirulina maxima (S. maxima) and Chlorella pyrenoidosa (C. pyrenoidosa), for their ability to remove methylene blue from aqueous solutions. These samples were chemically modified with orthophosphoric acid (H3PO4) and zinc chloride (ZnCl2) and compared with their respective unmodified samples in terms of equilibrium, kinetic and thermodynamic parameters. After the modification process, a change in the biosorbent surface was observed for all the samples. F. vesiculosus and C. pyrenoidosa had their oxygen content increased, as shown by energy x-ray spectrometer (EDS), proving their surface modification by the increase in carboxylic groups content. Enhanced thermal stability was attained in modified algae in comparison with unmodified. The best results in terms of maximum biosorption capacity after chemical modification were obtained for the samples F. vesiculosus modified with H3PO4 (1162.9 mg g(-1)) and C. pyrenoidosa modified with ZnCl2 (212.0 mg g(-1)), achieving an increase of 39.9% and 85.9%, respectively. For the green algae S. maxima, a reduction of 40.6% and 22.2% was observed after the activation process with H3PO4 and ZnCl2, however in either case the variation observed was considered non-significant (p > 0.05). The equilibrium was achieved after 40 min F. vesiculosus sample modified with H3PO4. For C. pyrenoidosa and S. maxima modified with ZnCl2 the equilibrium was achieved after 15 and 30 min, respectively. The biosorption process presented an exothermic nature and the predominance of physical interactions between the biosorbent and adsorbate. In general, the modified samples presented a superior performance, therefore being considered an efficient alternative to the conventional treatment forms. However, due to the competition between the different species present in the medium, smaller removal percentages were observed for dyes when compared to the metallic compounds. In general, the modified samples presented a superior performance, therefore being considered an efficient alternative to the conventional treatment forms. (C) 2019 Elsevier Ltd. All rights reserved.