Co-valorization of discarded wood pinchips and sludge from the pulp and paper industry for production of advanced biofuels

Abstract

Several lignocellulosic wastes are generated in the pulp and paper industry (PPI), such as small wood chips (pinchips) and paper sludge, presenting a high cellulose content suitable to be converted into biofuels or bio-products in a forest biorefinery scheme. In this work, two schemes of biorefinery were proposed for their valorization, processing small eucalyptus wood pinchips in two different strategies: (i) autohydrolysis at 230ºC, and (ii) autohydrolysis at 195ºC followed by organosolv process (47.7% ethanol-water, 198ºC for 60 min). More than 95% of cellulose was recovered in both schemes. In the combined process, 76% of delignification was achieved and 78% of xylan was solubilized as xylooligosaccharides. To reduce operational cost of lignocellulosic biomass-to-ethanol fermentation, the mixture of the treated eucalyptus pinchips from two processes with sludge was also proposed to increase the initial glucan content and to supply a rich source of nitrogen (present in the sludge). For that, two experimental designs were carried out for ethanol production by simultaneous saccharification and fermentation (SSF) process. Ethanol from SSF assays using sludge as co-substrate at 0.6 g of sludge/g of treated wood pinchips and 16 FPU/g of pretreated solids allowed to obtain 59 g/L (90% of conversion) and 46 g/L (96% of conversion) when blended with the wood from autohydrolysis and with the wood from autohydrolysis followed by organosolv, respectively. Overall, this study shows an alternative process valorization of biomasses derived from PPI for production of advanced biofuels and bio-products (such as xylooligosaccharides and lignin) contributing to achieving a circular economy.