AbstractValorization of lignocellulosic feedstock from a Dutch elm disease tolerant Ulmus minor clone was studied as a new biomass resource. Herein, fermentable sugars and activated carbons from the side‐stream lignins were produced. For the sugar extraction organosolv and acid hydrolysis pretreatments prior to enzymatic hydrolysis were compared for the first time for this clone prior to enzymatic hydrolysis; organosolv was more efficient for delignification (49 %), while acid hydrolysis was more efficient at eliminating hemicelluloses (95 %). A high final glucose concentration of 22–23.5 g L−1 was obtained after enzymatic hydrolysis suggesting that this clone can be considered a potential source for glucose‐based biofuel production. The side‐stream lignins were converted to microporous biochars of high surface area (1220 m2 g−1) and micropore volume (0.42 cm3 g−1). These biochars exhibited excellent properties as electrodes in supercapacitors with a specific capacitance of 118 F g−1 and a high energy density of 14 Wh kg−1 at 7000 W kg−1, while they were also efficient adsorbents in water remediation of model contaminants.