Bioethanol production from paper sludge containing antiseptic and deinking agent by subcritical water pretreatment and semi-simultaneous saccharification and fermentation

Abstract

Abstract For a long time, bioethanol production from wood-based biomass has been investigated. However, most studies face issues including high costs and technical difficulties associated with delignification and saccharification. Paper sludge (PS) from paper mills has a significant potential for bioethanol production. In this study, waste-paper-containing PS is used as the raw material for bioethanol production because the annual waste paper utilization rate has increased. Although PS does not require delignification, the antiseptics and deinking agents in PS inhibit enzymatic reactions such as saccharification and fermentation and their removal has not yet been reported. Using subcritical water pre-treatment, the selective decomposition of enzyme inhibitors in PS is examined without the generation of other enzyme inhibitors. The optimum pretreatment conditions are identified as 240°C, 3.3 MPa, 3 min, and pH 4.5. Glucose was obtained in 71% yield from pretreated 5 wt% PS using cellulase, which is 5.5 times higher than that from unpretreated PS. This is because the reactivity of the pretreated PS increases with the surface area of the cellulose fibers, and the cellulase inhibitors are decomposed by subcritical water. Next, semi-simultaneous saccharification and fermentation treatments are performed to produce bioethanol from waste-paper-containing PS. The bioethanol yield based on cellulose after 96 h is 68% for PS pretreated with subcritical water, whereas the bioethanol yield is 6% for unpretreated PS. Therefore, subcritical water pretreatment increases the bioethanol yield by 11 times. Proposed method allows large amount of PS to be used as ethanol feedstock in future.