Bioadsorbents using malt bagasse from brewery waste

Resumo

The textile industry produces large volumes of effluents containing polluting chemical substances, such as dyes. Treating these contaminants is essential to minimize their socio-environmental impacts. [1]. A promising alternative is the use of agro-industrial waste, such as malt bagasse, which is abundant and inexpensive, as a bioadsorbent to remove dyes and heavy metals. [2] Thus, the goal of this work is to explore the potential of malt bagasse on methylene blue adsorption. The pristine, acid-modified (HCl, HNO3, H2SO4, and H3PO4) and activated carbon pyrolyzed at different temperature (500, 600, 700, and 800 °C) from malt bagasse were studied. These bioadsorbents were characterized by X-ray diffraction, indicating the presence of diffraction peaks at 16.4, 21.7° characteristics of lignocellulosic biomass (cellulose I), Fig. 1A (i). [3]. After the acid treatment, Fig. 1 (ii-v), there was no long-distance change in biomass structure. For activated carbons, Fig. 1A (ii-v), the cellulose I peak disappeared, suggesting a destruction of the lignocellulosic chains from malt bagasse; the presence of a diffraction peak at ~24° is consistent of a carbon amorphous arrangement. [1]. Just in CM@800, Fig. 1B (v), there was the appearance of peaks at 22 and 30° characteristics of inorganic minerals. The performance of bioadsorbents were evaluated by methylene blue adsorption at different concentrations (10–200 mg∙L-1 ), Fig. 1C. A highlight for MC@800, which removed 100% of methylene blue in all concentration studied. Meanwhile, the MB@HNO3 removed 100% of methylene blue in 50 and 100 mg∙L -1 concentrations. These bioadsorbents were submitted to the adsorption kinetics (180 min). Again, both adsorbents removed 100% of the methylene blue after 15 min, 200 mg∙L-1 for CM@800 and 100 mg∙L-1 MB@HNO3, respectively. According to the adsorption isotherms (not shown here), the CM@800 presented a characteristic kinetic profile of physisorption and the MB@HNO3, it displayed a chemisorption profile, respectively. This difference may be attributed to the oxidation of the malt surface (hydroxyl groups) in MB@HNO3, resulting in a stronger interaction with the methylene blue when compared to MC@800 bioadsorbent.