Abstract
BackgroundThe research aimed to improve the overall conversion efficiency of the CTec® family of enzymes by identifying factors that lead to inhibition and seeking methods to overcome these through process modification and manipulation. The starting material was pulp derived from municipal solid waste and processed in an industrial-scale washing plant.ResultsAnalysis of the pulp by acid hydrolysis showed a ratio of 55 : 12 : 6 : 24 : 3 of glucan : xylan : araban/galactan/mannan : lignin : ash. At high total solids content (>18.5% TS) single-stage enzyme hydrolysis gave a maximum glucan conversion of 68%. It was found that two-stage hydrolysis could give higher conversion if sugar inhibition was removed by an intermediate fermentation step between hydrolysis stages. This, however, was not as effective as direct removal of the sugar products, including xylose, by washing of the residual pulp at pH 5. This improved the water availability and allowed reactivation of the pulp-bound enzymes. Inhibition of enzyme activity could further be alleviated by replenishment of β-glucosidase which was shown to be removed during the wash step.ConclusionsThe two-stage hydrolysis process developed could give an overall glucan conversion of 88%, with an average glucose concentration close to 8% in 4 days, thus providing an ideal starting point for ethanol fermentation with a likely yield of 4 wt%. This is a significant improvement over a single-step process. This hydrolysis configuration also provides the potential to recover the sugars associated with residual solids which are diluted when washing hydrolysed pulp.
Highlights
The research aimed to improve the overall conversion efficiency of the CTec® family of enzymes by identifying factors that lead to inhibition and seeking methods to overcome these through process modification and manipulation
The Municipal solid waste (MSW) derived paper pulp showed a lignin concentration of 24% when compositional analysis was performed using the standard NREL method [40]
Sugar product inhibition could be alleviated using twostage hydrolysis with an intermediate fermentation step where both hydrolysis and fermentation were performed under their optimum process conditions
Summary
The research aimed to improve the overall conversion efficiency of the CTec® family of enzymes by identifying factors that lead to inhibition and seeking methods to overcome these through process modification and manipulation. It is envisaged that second generation bioethanol made from lignocellulosic materials will begin to contribute. The conversion of these materials to fermentable sugars has been researched widely over the last few years. The final steps required to make the process economic at a commercial scale are linked to achieving glucose concentrations that Meeting these requirements presents some challenges, as hydrolysis at high total solids concentrations can lead to a decrease in substrate conversion, sometimes referred to as the ‘solids effect’ [4,5,6]. There may be other, as yet unidentified, reasons for decreased conversion
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