Pretreatment and enzymatic hydrolysis of tertiary cellulose for glucose production

Tertiary cellulose, obtained from wastewater treatment plants, is described herein as an attractive and renewable feedstock for producing bio-based chemicals. It is composed of ca. 57 wt% cellulose and a cellulose-to-hemicellulose weight ratio of approximately 4 (comparable to toilet paper). The enzymatic hydrolysis of tertiary cellulose into glucose over a commercial cellulase enzyme catalyst was studied. At a tertiary cellulose loading of 5 % w/v, the yield of glucose could reach 94 mol% after 72 h of hydrolysis using 30 FPU/g substrate enzyme concentration. The hydrolysis rate was enhanced at higher enzyme dosages. However, the glucose yield tended to decrease at increased solid loadings especially at the late stage of hydrolysis, which is ascribed to high solids effect (e.g., liquid-solid mass transfer limitation and enzyme inhibition). Compared with other cellulosic sources including pulp and Avicel, tertiary cellulose is easily depolymerized and exhibited the highest glucose yield given its lowest crystallinity index. The work further explored the alkaline pretreatment of tertiary cellulose and the use of a fed-batch hydrolysis strategy to enhance the enzymatic saccharification. Pretreated tertiary cellulose using 1 M KOH at 90 °C for 1 h could provide a higher hydrolysis yield (84.6 mol% in 48 h compared with 79.4 mol% for untreated raw materials; using 10 % w/v substrate loading and 30 FPU/g dry substrate enzyme), though at the cost of a concomitant cellulose loss to some degree during the pretreatment. Despite the presence of scale-up effects, the advantages of fed-batch operation could be seen from the more or less constant glucose production rate maintained between consecutive batches, possibly due to the mitigated high solids effect and improved enzyme performance. • Tertiary cellulose from wastewater treatment plant is a renewable feedstock. • Tertiary cellulose hydrolysis by commercial enzyme gave 94 mol% glucose yield. • Tertiary cellulose has a lower crystallinity and higher digestibility than Avicel. • KOH-pretreated tertiary cellulose can give enhanced glucose yield in hydrolysis. • Fed-batch operation improved hydrolysis performance at high solid loadings.