Hemicellulose isolation, characterization, and the production of xylo-oligosaccharides from the wastewater of a viscose fiber mill

• The hemicellulose in the wastewater from a viscose fiber mill was studied in detail.
• The xylans in the hemicellulose were linear with a few side-chains attached.
• The hemicelluloses could be effectively isolated to produce XOS.
• The dilute H2SO4 pretreatment could improve the XOS yield.

Viscose fiber mills generate a lot of wastewater enriched with hemicelluloses. The structure of the hemicellulose in the wastewater was characterized and the hemicellulose was isolated to produce xylo-oligosaccharides (XOS). It was confirmed that the hemicellulose was mainly 4-O-methylglucuronoxylan with a small amount of glucomannan and xyloglucan. The 4-O-methylglucuronoxylan was completely de-acetylated and linear with a few 4-O-methyl glucuronic acid attached. After purified by the acid precipitation and washing, the hemicellulose was pretreated by dilute acid, and then subjected to xylanase hydrolysis. After the dilute H2SO4 pretreatment at pH 2.6 and 150 °C for 30 min and the followed xylanase hydrolysis (65 IU/g xylan), the total XOS yield was improved from 0.215 to 0.578 g/g xylan. The percentage of XOS in the final sugar product was 68.9%. These results demonstrated the potential economical and environmental benefits of the process to utilize the byproducts from viscose fiber mills.