DEFATTED SEED CAKES RECOVERY TO INCREASE BIOFUEL PRODUCTION SUSTAINABILITY FROM SECOND-GENERATION OIL-CROPS

The Renewable Energy Directive (RED II) requires biodiesel to reduce greenhouse gas (GHG) emissions by at least 65% compared to fossil fuels. Most first-generation oil crops cannot reach this threshold due to high costs and competition with food, while newgeneration oils, which have emerged in recent decades, are hardly scalable. In this context, second-generation oil crops show promising traits, such as inedible oil, low chemical input requirements, and potential cultivation on marginal lands. However, data on their sustainability are scarce and sometimes contradictory, and their ability to comply with RED II requirements remains unclear. To address this, valorisation of by-products from the biodiesel supply chain has been identified as a key strategy to improve sustainability. This PhD work focused on testing different valorisation pathways for defatted seed cakes (DSCs) from various second-generation oil crops. The first step adopted a comprehensive approach to include DSCs in a circular economy framework. Ricinus communis and Camelina sativa were cultivated over two seasons, in rotation. The chemical characteristics of the oil were compatible with biodiesel synthesis, while the biomethane potential (BMP) of the DSCs (up to 337 ± 15 NmlCH4 g TS-1 ), was comparable to maize silage. Combining double cropping, biogas production, digestate fertilisation, and nitrification inhibitors resulted in an 81% GHG reduction. The second step focused on the valorisation of DSCs from C. sativa, Brassica carinata, and Brassica juncea as animal feed. An in-depth chemical characterization, followed by a literature review, revealed their suitability as a protein source when included at 10% (w/w) of the total ration. AGHG reduction up to 70% was observed. The third step evaluated DSCs for biogas production. B. juncea produced the highest methane yield (366 ± 18 Nml CH₄ g⁻¹ TS). Continuous stirred tank reactor (CSTR) trials achieved a biomethane production of up to 314.5 ± 8.9 Nml g⁻¹ TS and a 85% yield vs. 2 theoretical potential. The results confirmed the potential of DSCs from second-generation oil crops as substrates for biogas production. The last valorisation pathway involved recovering compounds for the pharmaceutical market. C. sativa defatted seed cake (DSC) exhibited the highest total polyphenol content (5.9 mg GAE g⁻¹ TS) and radical-scavenging activity (45.8 µmol TE g⁻¹ TS), along with the highest cell viability (120%). These properties, comparable to those of common by-products, such as orange or tomato peels, support the use of DSCs as feedstocks for high-value products. Finally, an additional study unrelated to the recovery of DSCs, investigated the synthesis of bioethanol from second-generation energy crops, emphasizing environmental and economic sustainability. Biomass pretreatment optimisation was studied using two promising solvents, ethanolamine and chlolinium lysinate, in the pretreatment of Sorghum bicolor, Populus nigrum and Panicum virgatum. The combination of all three feedstocks pretreated with ethanolamine gave the highest sugar release (glucose 84.6%, xylose 76.6%). Overall, this PhD thesis met its objectives, advancing knowledge on second-generation energy crops and co-product valorisation through three main pathways. It also demonstrated that by-products recovery within a circular approach can enhance sustainability and resource efficiency, achieving up to 81% GHG emission reduction compared to fossil diesel.