An Exploratory Study of Hydrochar as a Matrix for Biotechnological Applications

This paper explores the potentialities of hydrochar in protein separation and enzyme immobilization for non-energy biorefinery applications of hydrothermal carbonization. An innovative experimental procedure monitors soluble protein-hydrochar interactions and enzymatic reactions in a continuously stirred tank reactor. The hydrochar comes from hydrothermal carbonization of silver fir (200 °C, 30 min, 1/7 solid/water ratio) and standard activation (KOH, oven, 600 °C). Bovine serum albumin, a non-active, globular protein, was adsorbed at ≤3300 mg/g. Sip's isotherms fitted data well (R² = 0.99999). The immobilization used a commercial β-glucosidase, which catalyzes the hydrolysis of cellobiose to glucose, a bottleneck of the cellulose to fermentable sugar bioconversion network due to the fast enzyme deactivation. The hydrochar adsorbed ≤26 w/w% of enzyme. The heterogeneous biocatalyst operational stability was 24 times that of the soluble one. The results encourage further investigations and foreshadow process schemes coupling hydrothermal carbonization and industrial bioconversions.