Adsorção de azul de metileno a partir do lodo de uma estação de tratamento de água

Abstract

Currently, significant efforts are being made to minimize water body contamination and the generation of harmful environmental waste. Textile industries, due to their high water consumption in the production of their goods, generate a significant amount of effluent. Among the primary components of textile effluent are dyes, and one of the main methods for dye removal is through adsorption. This study analyzes the production of two low-cost adsorbents using sludge from two water treatment plants (WTPs) in Manaus - one from a settling tank and the other from a flotation unit. To achieve this, an experimental design was conducted to determine the best conditions for the adsorption process. Adsorption isotherm tests were also performed, fitting the experimental data to Langmuir and Freundlich models to evaluate the favorability of removing methylene blue. This helped determine the maximum adsorption capacity and equilibrium parameters. For the preparation of the adsorbents, collection, drying, grinding, and sieving were performed, followed by chemical activation with H3PO4, and pyrolysis at 500°C for three hours to produce the adsorbents, ads-leta1, and ads-leta2. The materials were morphologically characterized by SEM. According to the results from the experimental design, the produced adsorbents achieved significant results with a mass of 0.10g and a temperature of 30°C for ads-leta1, reaching a removal percentage of 98.19%, and for ads-leta2, a temperature of 35°C and a mass of 0.12g achieved a removal percentage of 98.76%. Regarding the isotherm tests, they were designed based on the variables that had the most significant effect on removal, according to the results obtained from the experimental design. For ads-leta1, the mass had a significant effect, so the isotherms were constructed with varying masses (0.04; 0.07; and 0.10g) at a fixed temperature of 30°C. For ads-leta2, the most significant effect was temperature, so the isotherms were constructed with varying temperatures (30, 35, and 40°C) at a fixed mass of 0.12g. The data from the isotherm tests showed a better fit to the Freundlich model, indicating a heterogeneous multilayer process for both ads-leta1 and ads-leta2. The results showed a maximum adsorption capacity of 9.1402 mg.g-1 for ads leta1 and 2.5492 mg.g-1 for ads-leta2, suggesting that WTP sludge, when subjected to chemical and thermal treatments, serves as an alternative and low-cost raw material for the production of adsorbents used in dye removal.