Dual-Purpose Valorization of Olive Pomace: Energy Production and Agricultural Application via Hydrothermal Carbonization

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

Lime-assisted hydrothermal humification and carbonization of sugar beet pulp: Unveiling the yield, quality, and phytotoxicity of products

Hydrothermal carbonization (HTC) solid and liquid products may inhibit seed germination, necessitating post-treatment. The hydrothermal humification (HTH) method addresses this drawback by transforming inhibitory compounds, such as aromatics, into artificial humic acids (AHAs) and artificial fulvic acids (AFAs). This study introduces a novel approach by investigating the substitution of the commonly used alkaline agent in HTH, KOH, with hydrated lime to develop cost-effective hydrothermal fertilizers from sugar beet pulp, enriching them with AHAs. It assesses the effects of lime on AHA production and soluble organic compounds compared to KOH. The results indicate that lime significantly reduces furans (from 560 to 3.15 mg/kg DM in solid and from 344 to 3.86 mg/L in process liquid) and boosts sugars and organic acids, especially lactic acid (from 4.70 to 65.82 g/kg DM in solid and from 4.05 to 22.89 mg/L in process liquid), increasing hydrochar yield (68.8% with lime vs. 27.4% with KOH). Despite the lower AHA production with lime compared to KOH (3.47% vs. 15.50%), lime-treated hydrothermal products are abundant in calcium and magnesium, boasting a pH of 7. This property presents a safer and more efficient alternative to hydrothermal fertilizers. The characterization of AHAs aligns with standard and natural humic substances, while lime-assisted HTH products, applied at a level of 0.01% w/w, could significantly enhance wheat growth and nutrient uptake compared to the control group. Importantly, these products show no toxicity on Daphnia magna, underscoring their potential for sustainable agriculture