Análise da recuperação de fósforo através da carbonização hidrotérmica de resíduos alimentares

Abstract

Phosphorus is an irreplaceable and essential nutrient for plant growth, being one of the main constituents of agricultural fertilizers. The main source of phosphorus is phosphate rock, which is already considered a critical raw material as it’s not renewable. This fact generated a lot of recovery phosphorus researchs from alternative raw materials. The main objective of this work was to evaluate the different conditions in the hydrothermal carbonization (HTC) of food waste (RA), for the recovery of phosphorus in the solid product (hydrochar - HC), in addition to verifying the energetic properties of the formed HC. The RAs were collected from popular restaurants in Bagé city in Rio Grande do Sul after lunchtime. Packaging and bones were removed from the process. The RAs were ground for homogenization and frozen until use. Part of the residues were characterized in relation to immediate, thermogravimetric (TGA) and phosphorus content analyses, and the other part was for HTC. The RA had moisture, volatile, fixed carbon and ash contents of approximately 55, 44, 2 and 2% respectively, and did not form a sufficient amount of phosphorus precipitate for quantification. The formed HCs were characterized in relation to immediate, TGA, calorimetric and phosphorus content analyses. The HCs formed at 200°C (HC-200°C), at 250°C (HC-250°C) and at 300°C (HC-300°C) obtained approximately 36,0, 26,5 and 16,0% of moisture respectively. The volatile material, ash and fixed carbon contends on HCs were determined on a dry basis, being approximately 63, 3 and 35% for HC-200 °C respectively, 56, 3 and 41% for HC-250 °C and 44, 2 and 54 for HC-300°C. From the TGA analysis, it was verified which the HCs present two peaks of mass decay, the first corresponding to volatiles and the second to lignin and proteins. The calorific value for the hydrochars HC-200 °C, HC-250 °C and HC-300 °C were 48, 53 and 49 MJ.kg-1 respectively. HC-250 °C had a small phosphorus content of 0.35%, but a high fixed carbon content. This procedure was efficient because it concentrated nutrients in the HC. Even low amounts, it was possible to detect phosphorus in the HC. The HC has better fuels proprieties than coal.