This study explores the hydrothermal carbonization (HTC) of olive pomace under varying conditions of temperature (180, 200, and 220 °C) and holding time (0 and 1 h) to identify the best valorization path for the resulting by-products. The hydrochars produced displayed a higher carbon content and lower oxygen and ash content compared to the feedstock, resembling the characteristics of solid fuels and suggesting their potential as sustainable energy sources. The liquid by-product (process water), was assessed for its effects on the germination of cress seeds (Lepidium sativum L.), revealing that while
lower concentrations enhance seedling growth, higher concentrations exhibit significant phytotoxic effects. The study concludes that with appropriate dilution, process water can be effectively utilized in agriculture, aligning with sustainable waste management practices, and contributing to a circular approach
