Coffionic Fractionation of Horse Manure: Improving Methane Yield and Enzymatic Lignin Functionalization for Tailored PLA–Lignin Materials

Horse manure is an abundant lignocellulosic feedstock with potential for circular biorefineries to diversify and upgrade the methane value chain. However, integrated fractionation strategies enabling the simultaneous valorization of both polysaccharides and lignin remain poorly explored. Here, we developed the Coffionic strategy, a closed-loop, green iono-organosolv fractionation combining, in a two-step, one-batch approach, the eco-acceptable ionic liquid 1-ethyl-3-methylimidazolium acetate and the food-grade solvent 2-methyltetrahydrofuran-3-one, with full solvent recovery and recycling. This strategy selectively recovered 70% w/w of the lignin from horse manure, yielding a Coffionic lignin fraction with a purity of 78% w/w and less than 2.5% w/w of residual sugars. The resulting polysaccharide-rich fraction showed enhanced enzymatic digestibility, achieving >99% cellulose conversion and increasing the biochemical methane potential by 17% compared with untreated horse manure. Coffionic lignin was further upgraded by enzymatic transesterification using immobilized Novozym435® in the same food-grade solvent employed for fractionation, yielding lignin esters compatible with PLA. Esterified lignin–PLA films reached a total surface energy significantly higher than neat PLA and unmodified lignin–PLA films. Overall, the Coffionic strategy provides an integrated and low-waste biorefinery route enabling the simultaneous production of biomethane and high-value lignin-based materials from horse manure.