Estudo comparativo da vagem da algaroba in natura e com ativação química para a adsorção de oxitetraciclina

Abstract

The pollution caused by the improper disposal of waste, including pharmaceuticals such as oxytetracycline (OTC), poses a threat to aquatic ecosystems and public health. OTC, widely used in aquaculture, is poorly metabolized and released into the environment, contributing to the emergence of resistant bacteria. In this study, the adsorption potential of biomass from the pod of Prosopis juliflora (algaroba), in both raw and chemically treated forms, was investigated for the removal of OTC in aqueous solution. The adsorbents were obtained by drying at 60, 70, and 80 °C to evaluate the influence of temperature on adsorption. They were then ground, sieved, and treated with HCl and NaOH, and characterized by FTIR and the point of zero charge (pHPZC). Mathematical modeling indicated that the two-term exponential model best described the drying process. Statistical tests showed that temperature did not significantly influence adsorption, allowing the choice of 60 °C for energy savings. Four samples were prepared: raw (ING40), treated with HCl (TAG40) and NaOH (TBG40) with particle sizes between 0.420 and 0.149 mm, and one raw sample with particles < 0.149 mm (ING100). The pHPZC values were 5.20 (raw), 3.20 (HCl-treated), and 7.10 (NaOH-treated). The mixed Box-Behnken experimental design revealed that all variables were statistically significant. The adsorbent mass was the most influential factor in adsorption capacity (Qt), followed by OTC concentration, material condition, contact time, and pH. The conditions to maximize Qt were: 0.2 g of adsorbent, 80 mg/L of OTC, pH 4.0, 90 minutes of contact time, and the use of raw adsorbent. The second design compared the particle sizes of raw materials, ING40 and ING100, showing that smaller particles resulted in higher values of Qt and removal efficiency. Kinetic assays showed that the pseudo-second-order model best fit ING40, while ING100 was better described by the pseudo-first-order model. Regarding isotherms, the Sips model was the most suitable for both samples, with maximum adsorption capacities of 253 mg/g and 329 mg/g. It is concluded that the Prosopis juliflora pod shows great potential as an adsorbent for OTC removal, representing a promising, low-cost, and sustainable alternative for the treatment of contaminated water.