Avaliação do potencial energético e das propriedades físico-químicas de insumos, produtos e resíduos de um biodigestor anaeróbico

Abstract

Population and industrial growth have intensified the generation of waste, especially organic waste. Organic waste that is discarded can represent an opportunity for energy reuse. In this context, anaerobic digesters have emerged as a sustainable solution, transforming organic matter into biogas and biofertilizer. This work evaluates the energy potential and physical-chemical properties of raw material, products and residues from the anaerobic biodigestion of food waste. The characterization of the input material for biodigestion consisted of obtaining the moisture, volatile matter, ash and fixed carbon contents by immediate analysis, carbon, oxygen and hydrogen composition by elemental analysis and nitrogen by the Kjeldahl method, as well as obtaining the higher calorific value using a calorimetric pump. For biogas, ABNT NBR 15.213:2008 and 14.903:2014 standards were used to obtain its physical properties in conjunction with chromatographic analysis. The digestate was characterized by reading its pH and electrical conductivity, quantifying the nitrogen content and growing it in vivo. Microorganisms were isolated from the biodigestion residue in selective nutrient agar, potato-dextrose and nitrogen-free media, and the synthesis of phytohormones was assessed in tryptone soy broth culture medium. The organic input had high levels of moisture (70.09%), volatile matter (83.78%), ash (4.16%) and fixed carbon (12.05%), as well as high concentrations of carbon (45.80%) and oxygen (43.55%), and lower concentrations of hydrogen (5.82%) and nitrogen (1.73%). Its calorific value was 19.25 MJ·kg-1. The biogas was 54.59% methane, 29.26% carbon dioxide, 12.03% nitrogen and 4.12% oxygen, with a lower calorific value of 17.97 MJ·m-3, an absolute density of 1.08 kg·m-3 and a compressibility factor of Z=0.9978. The digestate had an electrical conductivity of 8.33 mS·cm-1 and a nitrogen content of 9.26%. The 75% dilution promoted greater plant development, with emergence in 6 days, a germination rate of 67%, an average number of leaves equal to 6, a leaf area of 79.15 cm2, a stem length of 7.50 cm, a stem diameter of 0.50 cm and a maximum root length of 49.90 cm. However, statistical tests (ANOVA and Tukey, p<0.05) revealed that the stem diameter, maximum root length and number of leaves were not directly influenced by the concentrations of biofertilizer. The soil analysis revealed that the digestate significantly increased its fertility, with an increase in phosphorus, potassium and calcium levels, a reduction in exchangeable acidity and aluminium, and stabilization of the magnesium concentration. However, exchangeable acidity showed no significant correlation with digestate dilution (p≥0.05). The bioprospecting of microorganisms resulted in the isolation of three colonies in NFB selective medium with a concentration of 10-6 internal residue, with significant production of indole-3-acetic acid in TBS medium with a maximum value of 165.43 μg·ml-1. However, no isolate showed the ability to solubilize phosphate. In this way, this study highlights the importance of energy recovery from food waste for the anaerobic biodigestion process, as well as contributing to research into biofuels, biofertilizers and inoculants.