Efficient production of ethanol from waste paper and the biochemical methane potential of stillage eluted from ethanol fermentation

Abstract Waste paper can serve as a feedstock for ethanol production due to being rich in cellulose and not requiring energy-intensive thermophysical pretreatment. In this study, an efficient process was developed to convert waste paper to ethanol. To accelerate enzymatic saccharification, pH of waste paper slurry was adjusted to 4.5–5.0 with H 2 SO 4 . Presaccharification and simultaneous saccharification and fermentation (PSSF) with enzyme loading of 40 FPU/g waste paper achieved an ethanol yield of 91.8% and productivity of 0.53 g/(L h) with an ethanol concentration of 32 g/L. Fed-batch PSSF was used to decrease enzyme loading to 13 FPU/g waste paper by feeding two separate batches of waste paper slurry. Feeding with 20% w/w waste paper slurry increased ethanol concentration to 41.8 g/L while ethanol yield decreased to 83.8%. To improve the ethanol yield, presaccharification was done prior to feeding and resulted in a higher ethanol concentration of 45.3 g/L, a yield of 90.8%, and productivity of 0.54 g/(L h). Ethanol fermentation recovered 33.2% of the energy in waste paper as ethanol. The biochemical methane potential of the stillage eluted from ethanol fermentation was 270.5 mL/g VTS and 73.0% of the energy in the stillage was recovered as methane. Integrating ethanol fermentation with methane fermentation, recovered a total of 80.4% of the energy in waste paper as ethanol and methane.