A biotechnological platform for the valorization of textile waste blend

Textile waste is rapidly increasing worldwide due to rising clothing consumption and production. This study presents a novel, integrated green process for degrading and valorizing blended cotton-polyethylene terephthalate (PET) textile waste into value-added chemicals through enzymatic hydrolysis and microbial fermentation. To improve degradation efficiency, specific pretreatments were developed for both cotton and PET. The process begins with mechanical ball-milling, followed by enzymatic hydrolysis of cotton using a commercial cellulases/hemicellulases cocktail at 55 °C to yield glucose. Next, the material undergoes thermal treatment at 290 °C for 15 min to prepare PET for enzymatic hydrolysis, which is then carried out at 55 °C using the S101N/F243T-ΔLCC PET-hydrolyzing enzyme variant. This approach resulted in complete conversion of cotton to glucose and ≥95 % conversion of PET to terephthalic acid (TPA) and ethylene glycol. TPA was further biotransformed with ≥90 % yield into protocatechuic acid (PCA)-a valuable aromatic compound-using an engineered E. coli strain expressing three enzymes from Comamonas sp. strain E6, namely the terephthalate dioxygenase TPADO α/β, the reductase TPADO RED, and the dehydrogenase DCDDH. The strain also utilized glucose from cotton hydrolysis as a carbon source. In total, 217.3 mg of PCA were produced from 249.2 mg of TPA (94 % yield) in 50 mL of a 30 mM substrate solution. From 1 g of polycotton fabric (30 % cotton, 70 % PET), approximately 500 mg of PCA (92 % yield) were generated. This integrated biorefinery process highlights a promising strategy for sustainable textile waste valorization.