Conversion of tertiary cellulose to bio-based chemicals
In her thesis, Elchin Jafariyeh Yazdi explores the conversion of tertiary cellulose—a waste-derived material from wastewater treatment—into bio-based chemicals, focusing on enzymatic hydrolysis and process optimization. Tertiary cellulose, with ~57% cellulose content and low crystallinity, showed high digestibility, achieving up to 98 mol% glucose yield at 5% solids without pretreatment. Mild alkaline pretreatment removed lignin and hemicellulose but did not improve yields, while a fed-batch strategy alleviated mass transfer limitations at higher loadings.
Jafariyeh Yazdi investigated enzyme recycling to address high enzyme costs. Ultrafiltration enabled reuse but suffered from enzyme losses due to adsorption and inactivation, especially at higher solid loadings. At the third recycling step, glucose yield losses correlated with declines in enzyme activity. Low substrate-to-enzyme ratios favored both yield and recovery, while high ratios caused poor retention. Product inhibition further reduced glucose production, underscoring the importance of enzyme management.
With a techno-economic analysis, Jafariyeh Yazdi compared 2 wt% and 10 wt% solid loading processes using continuous stirred-tank reactors with enzyme recycling. The 10 wt% scenario yielded 448.05 g/L glucose at €1/kg, with an 18% first-year ROI and 5-year payback, proving more economically favorable.
Jafariyeh Yazdi also examined fractionation using deep eutectic solvents ([ChCl:BA:PEG-400]), achieving effective lignin removal but lower subsequent glucose yields, indicating that cellulose accessibility remained limited despite delignification.
Overall, this work demonstrates that tertiary cellulose is a promising, renewable feedstock with high enzymatic digestibility. Process optimization through fed-batch operation, enzyme recycling, and appropriate fractionation is critical to improving both technical performance and economic viability.