Estudo da remoção do pesticida metomil em efluentes simulados por biossorção em bagaço de laranja residual
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2020-01-30
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Universidade Federal de Goiás
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This work consisted of studying the use of residual orange pomace from the juice processing industry as an adsorbent for the removal of methomyl, an extremely toxic carbamate pesticide, prepared in the laboratory as a synthetic aqueous solution to simulate the washing effluent of equipment used in activities spraying. Initially, the biosorbent biomass was subjected to surface characterization by means of scanning electron microscopy (SEM) and infrared spectroscopy (FTIR). From the images obtained by SEM it was possible to observe many irregularities on the surface of the adsorbent particles, however it was not possible to visualize macro or micro pores, denoting little porous particles. The study of the spectrograms obtained by FTIR revealed the presence of hydroxyl, carbonyl and carboxylic groups on the surface of the adsorbent particles. The biosorption tests were carried out in three stages. The first stage consisted of batch tests. The kinetics, the isotherm and the effects of pH and solid/liquid ratio (R) were evaluated, using the Central Rotational Composite Design 22 (DCCR 22), on the adsorption capacity of metomil in orange pomace particles (q). The second stage consisted of biosorption tests in pilot columns of 1 cm in diameter and fixed bed of orange bagasse of 30 cm, operated in continuous upward flow. In this step, the effects of flow (1, 5 and 10 mL) and the initial concentration of the affluent solution (20 and 50 mg.L−1) on the process were evaluated. Finally, the third step consisted of scaling up the biosorption column. Two systems were evaluated, System 1, consisting of two tubes 100 mm in diameter, one bed of 50 cm high orange pomace followed by a bed of foam 100 cm high, and System 2, consisting of three tubes 100 mm in diameter, being a bed of “gravel 2” 100 cm high, followed by a bed of orange pomace
100 cm high, followed by per 100 cm high foam bed, both operated in continuous upward flow. During the operation of System 1, elementary analysis was performed by fluorescence spectroscopy with total X-ray reflection (TXRF), of samples of affluent and effluent solutions, in order to qualitatively and quantitatively assess which elements had the greatest influence on the biosorption process of metomil in orange pomace. In batch tests, a better fit was obtained for the pseudo-second order kinetic model (R2 = 0.949), concluding that the chemisorption was the controlling step of the process. The Langmuir isotherm model fitted better to the experimental data (R2 = 0.989) confirming the adsorption in monolayers, without interaction between the adsorbate molecules. The statistical study of the effects of pH and the solid/liquid ratio (R) on the adsorption capacity of methomyl in the orange pomace particles resulted in higher values of adsorption capacity (q = 3.73 and q = 3.43 mg.g−1), obtained at pH 6.0 and 4.5 with R values equal to 0.017 and 0.015 (g.mL−1), respectively. Thus, it was concluded that there was greater adsorption in tests containing a greater mass of adsorbent at slightly acidic pH. The study of the effects of the flow and the initial concentration on the biosorption of methomel in orange pomace carried out in the columns on a pilot scale demonstrated that the increase in flow increased the mass transfer rate and, consequently, the biosorption capacity of the bed, however it took to faster bed saturation, with steeper rupture curves. On the other hand, in the tests with lower flow, the adsorvate had a longer time of contact with the biosorbent particles resulting in greater removal of the pesticide. The increase in the concentration of the solution fed to the column resulted in a greater driving force in the mass transfer process and, consequently, in a greater biosorption capacity of the bed. The two full-scale treatment systems, System 1 and System 2, achieved removal of 57.88% and 50.53%, respectively, noting that the adsorption technology for the treatment of effluents contaminated with the metomil pesticide proved to be quite promising. The elementary analysis, by TXRF, showed that the leaching, mainly of Ca2+ and K+ salts, may have caused the vacancy of active sites, providing increased removal of methomyl by adsorption in the adsorbent particles of residual orange bagasse.
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ZIMMER, T. R. Estudo da remoção do pesticida metomil em efluentes simulados por biossorção em bagaço de laranja residual. 2020. 134 f. Tese (Doutorado em Química) - Universidade Federal de Goiás, Goiânia, 2020.