Abstract
BackgroundEthanol production from paper sludge (PS) by simultaneous saccharification and fermentation (SSF) is considered to be the most appropriate way to process PS, as it contains negligible lignin. In this study, SSF was conducted using a cellulase produced from PS by the hypercellulase producer, Acremonium cellulolyticus C-1 for PS saccharification, and a thermotolerant ethanol producer Saccharomyces cerevisiae TJ14 for ethanol production. Using cellulase of PS origin minimizes biofuel production costs, because the culture broth containing cellulase can be used directly.ResultsWhen 50 g PS organic material (PSOM)/l was used in SSF, the ethanol yield based on PSOM was 23% (g ethanol/g PSOM) and was two times higher than that obtained by a separate hydrolysis and fermentation process. Cellulase activity throughout SSF remained at around 60% of the initial activity. When 50 to 150 g PSOM/l was used in SSF, the ethanol yield was 21% to 23% (g ethanol/g PSOM) at the 500 ml Erlenmeyer flask scale. Ethanol production and theoretical ethanol yield based on initial hexose was 40 g/l and 66.3% (g ethanol/g hexose) at 80 h, respectively, when 161 g/l of PSOM, 15 filter paper units (FPU)/g PSOM, and 20% inoculum were used for SSF, which was confirmed in the 2 l scale experiment. This indicates that PS is a good raw material for bioethanol production.ConclusionsEthanol concentration increased with increasing PSOM concentration. The ethanol yield was stable at PSOM concentrations of up to 150 g/l, but decreased at concentrations higher than 150 g/l because of mass transfer limitations. Based on a 2 l scale experiment, when 1,000 kg PS was used, 3,182 kFPU cellulase was produced from 134.7 kg PS. Produced cellulase was used for SSF with 865.3 kg PS and ethanol production was estimated to be 51.1 kg. Increasing the yeast inoculum or cellulase concentration did not significantly improve the ethanol yield or concentration.
Highlights
Ethanol production from paper sludge (PS) by simultaneous saccharification and fermentation (SSF) is considered to be the most appropriate way to process PS, as it contains negligible lignin
The S. cerevisiae TJ14 strain did not consume xylose for ethanol production, and the ethanol concentration generated from xylose was almost 0 g/l (Figure 2B)
When a 10 g/l of glucose and mannose mixture at ratio of 85:15 was used as the carbon source, the ethanol concentration was 5.1 g/l and the Ye/glc was 87.8% (Figure 2C), which corresponds to a 88% theoretical ethanol yield [22]
Summary
Ethanol production from paper sludge (PS) by simultaneous saccharification and fermentation (SSF) is considered to be the most appropriate way to process PS, as it contains negligible lignin. To remove hemicelluloses in the lignocellulosic material contained in recycled PS and cotton gin waste, mixing with steam treatment has been described as an effective pretreatment. This pretreatment method generated compounds that are toxic to the microorganism responsible for fermentation. An advantage of PS as a carbon source over other lignocellulosic materials in bioethanol production is that pretreatment is not required, since most of the lignin has already been removed during the pulping that forms part of the paper manufacturing process
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