Aplicação de resíduos da produção de polpa do açaí (Euterpe oleracea Mart.) como bioadsorvente no tratamento de efluentes sintéticos

Abstract

The presence of toxic dyes in industrial effluents deteriorates the environment. Several processes have been presented for a effective treatment in the removal of these pollutants. Among them, we can highlight the use of agro-industrial residues as biosorbents as an ecological and sustainable alternative. Thus, this work aimed to evaluate the agroindustrial residue (acai seeds (SA) from pulp production) as a bioadsorbent for the removal of methylene blue (MB) and remazol brilliant blue (RB) dyes in synthetic effluents. The seeds were chemically modified with NaOH and H3PO4 0.1 mol/L solutions, being named SAB and SAA, respectively. The biosorbents were characterized through the techniques of determination of surface groups, determination of organic matter content, point of zero charge, Infrared (FT-IR), scanning electron microscopy (SEM) and thermogravimetric analysis (TG). For the optimization of the adsorption process, the parameters of pH, adsorbent mass, dye concentration, time and temperature were varied. Under optimized conditions (pH 8, 100 mg of bioadsorbent, 120 min for SAB and 600 min for SA and SAA, 200 mg/L of dye and temperature of 35 °C for SA, 30 °C for SAA and 20 °C for SAB ), the percentages of MB removal were extremely relevant 95.83; 99.11 and 99.41% for SA, SAA and SAB, respectively. For the RB (pH 2, 200 mg of bioadsorbent, 240 min for SAB and 360 min for SA and SAA, 40 mg/L of dye and temperature of 45 °C for SA and SAB and 15 °C for SAA), the percentages of removal were 97.11, 95.73 and 94.20% for SA, SAA and SAB, respectively. The Langmuir model showed the best fit (R2 = 0.9999). The thermodynamic parameters were also determined, where negative values of Gibbs free energy (∆𝐺) were observed for the processes with the three bioadsorbents in the adsorption of MB, indicating the spontaneity of the adsorption process, and positive values for the RB, showing the need to add energy to the system. MB adsorption was exorthermic while RB was mostly endothermic. Furthermore, for the three bioadsorbents, the process that occurred was physisorption (ΔH < 20 kJ/mol). Thus, the bioadsorbents produced from açaí seeds were effective in removing dyes in synthetic effluents, providing a sustainable use of a forest by-product through its application in effluent treatment systems.