Bioconversion of Kraft Paper Mill Sludges to Ethanol by SSF and SSCF

Abstract

Paper mill sludge is a solid waste material composed of pulp residues and ash generated from pulping and paper making processes. The carbohydrate portion of the sludge has chemical and physical characteristics similar to pulp. Because of its high carbohydrate content and well-dispersed structure, the sludges can be biologically converted to value-added products without pretreatment. In this study, two different types of paper mill sludges, primary sludge and recycle sludge, were evaluated as a feedstock for bioconversion to ethanol. The sludges were first subjected to enzymatic conversion to sugars by commercial cellulase enzymes. The enzymatic conversion was inefficient because of interference by ash in the sludges with the enzymatic reaction. The main cause was that the pH level is dictated by CaCO3 in ash, which is two units higher than the pH optimum of cellulase. To alleviate this problem, simultaneous saccharification and cofermentation (SSCF) using cellulase (Spezyme CP) and recombinant Escherichia coli (ATCC-55124), and simultaneous saccharification and fermentation (SSF) using cellulase and Saccharomyces cerevisiae (ATCC-200062) were applied to the sludges without any pretreatment. Ethanol yields of 75-81% of the theoretical maximum were obtained from the SSCF on the basis of total carbohydrates. The yield from the SSF was also found to be in the range of 74-80% on the basis of glucan. The SSCF and SSF proceeded under stable condition with the pH staying near 5.0, close to the optimum for cellulase. Decrease of pH occurred due to carbonic acid and other organic acids formed during fermentation. The ash was partially neutralized by the acids produced from the SSCF and SSF and acted as a buffer to stabilize the pH during fermentation. When the SSF and SSCF were operated in fed-batch mode, the ethanol concentration in the broth increased from 25.5 and 32.6 g/L (single feed) to 45 and 42 g/L, respectively. The ethanol concentration was limited by the tolerance of the microorganism in the case of SSCF. The ethanol yield in fed-batch operation decreased to 68% for SSCF and 70% for SSF. The high-solids condition in the bioreactor appears to create adverse effects on the cellulase reaction.

Effective saccharification of kraft pulp by using a cellulase cocktail prepared from genetically engineered Aspergillus oryzae

“…This yield was higher than that in previous report. 11) It has been reported that ethanol yields of 75-81% of the theoretical maximum were obtained from the SSF of kraft paper mill sludge, cellulase cocktail, and yeast. In contrast, no detectable amount of ethanol was produced without the addition of cellulase cocktail even after 72 h of fermentation (Supplemental Fig.…”

Advances in consolidated bioprocessing systems for bioethanol and butanol production from biomass: a comprehensive review

“…Previously, this technology has been used for production of both ethanol (e.g. Teixeira et al, 1999Teixeira et al, , 2000Kang et al, 2010) and lactic acid (e.g. Patel et al, 2005;Zhu et al, 2007).…”

“…Co-cultures or microbial consortia may also be utilized in the CBP systems as the third methodology. Brandon et al 2011Kang et al, 2010Kim et al, 2008Geddes et al, 2011Nieves et al, 2011Mullinnix, 2014Yang et al, 2014Jin et al, 2014 Jin et al 2012aOhgren et al 2006Wang et al, 2014aYasuda et al, 2014Zhu et al, 2014Fonseca et al, 2011Teixeira et al, 1999Jin et al, 2010Tang et al, 2011Zhang (J) et al, 2009Kim and Lee, 2005Zhang et al, 2012bYu et al, 2014Moreno et al, 2013Erdei et al, 2013aBallesteros et al, 2013Geddes et al, 2013Turhan et al, 2014Lan et al, 2013Hargreaves et al, 2013Alvira et al, 2011Olofsson et al, 2010a . In co-culture systems, saccharolytic and ethanologenic microorganisms are co-cultured to enhance efficient saccharification and fermentation in one pot.…”

Solid State Fermentation: Comprehensive Tool for Utilization of Lignocellulosic through Biotechnology

“…However, the commercial application of technology for transforming high carbohydrate content of the sludge into the value added products through SSF can support to meet the environmental and economic concerns. Using the sludge which generally contains low lignin content has been proven to be extremely proficient for its bioconversion into ethanol [72,73]. Moreover, it was also found quite successful for the ethanol production at commercial scale as they get the sludge as a waste free of cost since the sludge have no market value, pre-treatment can be eliminated and simultaneously the issue of the sludge disposal is also being compromised with no cost.…”