In-depth characterization of tertiary cellulose from wastewater treatment facilities

Specific wastewater streams from wastewater treatment facilities contain components with significant valorization potential, including cellulosic material derived from waste toilet paper. Quantifying cellulose and other carbohydrate content and identifying impurities is essential for developing efficient valorization strategies. In this study, tertiary cellulose (Recell®) obtained from a wastewater treatment facility was characterized to determine its overall chemical composition. Extraction with hexane, ethanol, and water gave a extractives removal of 9.3, 2.8, and 2.9 wt%, respectively mostly identified as fatty acids and esters (GC-MS). Detailed analyses of the extractive-free samples revealed the presence of cellulose (60 wt%), xylans (12 wt%), ash (8 wt%), proteins (5 wt%), and 2.5 wt% of residue after acid hydrolysis, which is normally associated with lignin. However, it was unequivocally proven (NMR, py-GC-MS) that lignin is not present and that this residue can be in part associated with plastic particles and proteins. After enzymatic digestion (48 h batch time), the glucose yield was 45 wt% for crude Recell® and 54 wt% for the extractive-free samples of the feedstock, and 81 and 90 wt% based on cellulose content, respectively. This shows that Recell® material is particularly cellulose-rich and that it can be readily converted into glucose. Removal of extractives can further enhance the enzymatic hydrolysis to facilitate valorization of this abundant residue stream. • Impurities of tertiary cellulose recovered from wastewater streams was revealed through in-depth characterization. • Cellulose composition in tertiary waste feedstock was about 60 wt%. • Lignin appeared to be absent from this type of biomass observed by 2D HSQC NMR and Py-GC-MS.