Speaker
Description
Hydrothermal carbonization (HTC) is increasingly recognized as a promising thermochemical process for the valorization of biowaste, enabling the conversion of lignocellulosic residues into a carbon-rich solid hydrochar and an aqueous liquid phase containing various organic compounds. In this study, HTC of waste wood was investigated, with particular emphasis on the chemical composition, antioxidant properties, and safety-related aspects of the resulting liquid phase. The process was performed at temperatures of 200 and 250 °C, liquid-to-solid ratios of 5:1 and 15:1, and residence times ranging from 30 to 165 min, under pressures between 192 and 584 psi.
Four selected liquid-phase samples obtained under different HTC conditions were characterized. The samples were strongly acidic, with pH values ranging from 2.7 to 3.1, and contained total organic carbon (TOC) concentrations between 211 and 550 mg C/L. Phenol concentrations varied from 16.9 to 75.8 mM, while total polyphenol content ranged from 0.352 to 0.588 g GAE/g. Pronounced antioxidant activity was observed in all samples, with DPPH radical scavenging values between 70.8 and 87.0%, indicating the presence of redox-active organic compounds formed during HTC.
To evaluate potential safety concerns, the liquid phase was analyzed for the 16 US EPA priority polycyclic aromatic hydrocarbons (PAHs) using gas chromatography–mass spectrometry (GC–MS) after liquid–liquid extraction.
The presence of PAHs was confirmed, suggesting that aromatic and potentially hazardous compounds may be generated or transferred into the aqueous phase during the HTC process.
Overall, the results indicate that the liquid phase obtained from HTC of waste wood is a chemically active by-product with both valorization potential and environmental relevance. Although its antioxidant activity suggests the presence of potentially valuable organic compounds, its acidic character, organic load, and confirmed PAH content emphasize the need for careful assessment and appropriate treatment before reuse or discharge.