Hydrothermal Liquefaction and Catalytic Hydrotreating of Food-Waste

Abstract

Institutional catering facilities generate large, continuous streams of food waste whose disposal carries environmental and economic costs, particularly in Mediterranean settings where landfill capacity and waste-management infrastructure are increasingly constrained. This work reports an integrated, experimentally grounded waste-valorization pathway that converts pre-sorted food waste from a Greek military academy canteen into a hydrotreated bio-oil, developed within the MARINES project. In the first stage, hydrothermal liquefaction (HTL) of the waste was carried out in 300–600 mL batch reactors at 280–320∘C, 100–130 bar, 10–20 wt% solids loading and 30–60 min residence time. Bio-crude higher heating value (HHV) increased with temperature, reaching approximately 39 MJ/kg at 320∘C, while the highest bio-crude quantities were obtained at 310∘C. In the second stage, a pooled bio-oil sample (baseline HHV 39.1±0.4 MJ/kg, O 7.5±0.2 wt%) was catalytically hydrotreated at 300–340∘C and 70–100 bar for 2 h using zeolite, aluminum(III) oxide and nickel(II) nitrate hexahydrate (5 wt% loading). At the optimum point (320∘C, 90 bar), the nickel-based catalyst performed best, raising HHV to 40.8±0.2 MJ/kg while lowering oxygen content to 6.4±0.1 wt%, outperforming aluminum oxide (HHV 40.4 MJ/kg, O 6.7 wt%) and zeolite (HHV 40.1 MJ/kg, O 6.8 wt%). Read together, the two data sets define a coherent production-to-upgrading chain and the operating windows in which each stage performs best. Beyond its technical content, the study is directly relevant to this journal’s focus on Mediterranean sustainability: it provides empirical, policy-relevant evidence for circular-economy valorization of an everyday institutional waste stream, with implications for waste-management planning, energy security, and decarbonization of public-sector facilities in Mediterranean-type economies.