Avaliação ecotoxicológica do nanobiocarvão produzido a partir de resíduos alimentícios de restaurante e cantina

Abstract

Nanobiochar is produced through controlled biomass pyrolysis processes, resulting in carbonaceous structures with high surface area, adjustable porosity, and a range of surface functional groups. These characteristics make nanobiochar attractive for various applications, including pollutant adsorption, energy storage, sensors, and catalysis. The aim of this study was to evaluate the ecotoxicity of nanobiochar produced from food waste collected from the restaurant and cafeteria of the Francisco Beltrão Campus at UTFPR. Samples were collected on consecutive days, and due to menu variations, the biomass consisted of various types of food. The samples were dried, ground, and exhibited a low moisture content of 0.01%. The conversion of this material into nanobiochar was achieved through pyrolysis followed by ball milling for four hours. During the pyrolysis process, the levels of C, P, K, Ca, Mg, Fe, and Mn increased by 63.20%, 232.73%, 104.14%, 378.33%, 258%, 91.85%, and 199.70%, respectively. This phenomenon may be related to the removal of functional groups and the elimination of volatile compounds. The XRD spectrum of biochar ground for four hours presented an amorphous halo around 20 degrees in 2θ, characteristic of carbon. Additionally, Bragg diffraction peaks were observed at approximately 28, 31, 40, 45, 50, 58, 66, 73, and 75, which were attributed to the cubic phase of KCl and the tetragonal phase of SiCl₄. The presence of these crystalline phases is due to the organic compound's origin and the non-oxidative pyrolysis process applied during combustion. The average particle size was around 315 ± 2 nm. The dynamic light scattering (DLS) spectrum analysis suggests the presence of particle agglomeration and non-spherical shapes. In the thermogravimetric analysis, different weight loss ntervals were detected: between 50 and 100°C, a slight mass loss occurred, with a maximum drop of approximately 7%, probably due to the loss of moisture adsorbed by the material. Around 200°C, a sharp mass reduction was observed, indicating the release of volatile substances. This behavior may be related to the decomposition of organic compounds or the release of dissolved water, although the presence of volatile organic compounds is more likely. Between 600 and 800°C, two additional mass losses were identified, attributed to the decomposition of potassium chloride and sodium chloride. In the acute toxicity analysis, the toxicity factor for Daphnia magna was found to be 4, corresponding to moderate toxicity for this bioindicator in the short term. For chronic toxicity with Desmodesmus subspicatus, the toxicity factor was 128, meaning that even at relatively low concentrations, the biochar could already affect algal health, potentially compromising the aquatic ecosystem over time.