Mitigação do herbicida metribuzin em meio aquoso por adsorção em hidrochar de lodo de esgoto e bagaço de malte

Abstract

The increasing urbanization and industrialization challenge solid waste management, particularly sewage sludge and brewery-spent grain. The expanding sewage treatment infrastructure results in the production of sludge that requires careful treatment before disposal or recycling. Simultaneously, the rising demand for beverages like beer generates large amounts of brewery-spent grain, an organic waste with potential for various applications, ranging from animal feed to biogas production. Integrating solutions for managing these solid wastes is essential to minimize environmental impacts, promote recycling, and contribute to urban and industrial sustainability. In the agricultural sector, herbicides like Metribuzin are used to control weeds for the cultivation of crops such as soybeans, corn, and others. However, after application, this product can accumulate in the soil and, over time, migrate to groundwater or surface waters. Focusing on waste recycling, the present work developed hydrochar, derived from a mixture of sewage sludge and brewery spent grain, through hydrothermal carbonization and applied it to remove the environmental pollutant Metribuzin via adsorption. For the synthesis of hydrochar, a 24 factorial experimental design was carried out to evaluate the parameters: temperature, solid fraction, mixture of sewage sludge and brewery spent grain, and reaction time, in the adsorption capacity, qe (mg.g-1). Statistical analysis indicated the best conditions for hydrochar synthesis: temperature of 180ºC, with a proportional mixture of biomasses (50% brewery-spent grain and 50% sewage sludge), the dosage of 0.43, 0.11, and 0.23 as central points, and a synthesis time of 4 hours. Kinetic tests were conducted with the best hydrochar determined, where the pseudo-second-order model best fitted the experimental data. For adsorption equilibrium, the Freundlich isotherm had a better fit at most of the temperatures studied. Thermodynamic calculations indicated a non-spontaneous process, physical adsorption, and low entropy. A toxicity test was also conducted, where it was observed that the three studied concentrations of adsorption effluent (200, 300, and 500 mg.g-1) did not inhibit the germination of A. cepa seeds. Root growth inhibition was observed at all three concentrations, but the two lower concentrations after the adsorption process were not phytotoxic, unlike the highest concentration.