Hydrothermal degradation of β-estradiol and oxytetracycline at selective reaction severities

Abstract: Hydrothermal carbonization (HTC) is a thermochemical process that produces biofuels and carbon-based materials from wastes; the solid product is commonly known as hydrochar. However, the fate of common pharmaceutical products during HTC has not been explored extensively. Knowledge on degradation pathways for emerging contaminants is important for further application of hydrochar, especially for water purification and soil amendment. Therefore, the objective of this study was to investigate the degradation of two emerging pollutants (i.e., oxytetracycline and 17β-estradiol) with HTC temperature, residence time, and initial chemical states. High-performance liquid chromatography and gas chromatography–mass spectroscopy (GCMS) were used to analyze the levels of degradation of oxytetracycline and β-estradiol and the secondary products generated due to their primary degradations, respectively. The results showed that the degradation of oxytetracycline and β-estradiol did not depend significantly on the HTC temperature and residence time. However, their degradation depends significantly on the initial pH of the solution. The maximum degradation of oxytetracycline and β-estradiol was observed at 84.1 ± 2.9% and 100% at initial pH 8 and pH 3, respectively. GCMS results showed that stable acidic compounds (such as benzoic acid and furoic acids) were produced due to the degradation of both oxytetracycline and β-estradiol in most of the experimental conditions. Graphic abstract: Synopsis: Degradation of both oxytetracycline and β-estradiol mainly produced benzoic acid and other functionalized monocyclic aromatics [Figure not available: see fulltext.]