Sustainable phosphorus recovery from digestive municipal waste via hydrothermal carbonization and recrystallization techniques

Abstract

Hydrothermal carbonization (HTC) is a highly promising method for converting wet biomass waste into potentially valuable materials. This thesis investigates the effectiveness of HTC in treating digestive sludge (DS). It examines how different temperatures ranging from (160°C to 200°C) and reaction periods at 30 minutes reaction affect the distribution of the resulting products and the recovery of phosphorus (P). In addition, we conducted the studies under two conditions: with and without addition of citric acid. We aimed to explore ways to enhance P solubilization in the liquid phase. We want to find the best conditions to get more P out of hydrochar and make the liquid phase better for the crystallization process that makes triple superphosphate (TSP) and diammonium phosphate (DAP) fertilizers. The best conditions (200°C, 30 minutes, 0.4 g citric acid) yielded a phosphorus concentration of 930 ppm. This demonstrates that citric acid significantly improves phosphorus solubilization. Ensuring accurate regulation of the reaction time was essential to avoid the unwanted reformation of phosphorous into the hydrochar through recrystallization. This study makes a significant contribution to the sustainable management of biomass waste by introducing a new technique for recovering phosphorus and providing important insights into the factors that affect the hydrothermal treatment process. The findings have important implications for improving nutrient reuse in waste treatment processes and encouraging sustainable methods by creating efficient bio-based fertilizers.