Enzyme recovery and fouling mitigation by ultrasound-enhanced ultrafiltration

Abstract

The development of second-generation biofuels from cellulosic/lignocellulosic biomass has advantages from energy and environmental aspects, but the overall cost of the process is mainly dependent on the cost of the enzymes. Enzyme recovery and recycling is one of the most important and effective means of increasing the efficiency of enzymatic hydrolysis processes by lowering the enzyme costs. The primary objective of this study was to investigate the possibilities of enzyme recovery by membrane separation. Ultrafiltration (UF) membranes with various cut-off values and materials were used to recycle cellulase and cellobiase in model solutions and cellulosic hydrolysates. The membrane separation process was followed by determination of the flux, and its efficiency of it was measured via sugar and protein retention, and the resistances were also calculated. A polyether–sulfone membrane with a cut-off value of 5 kDa, (PES5) operated at 26.8 L m⁻² h⁻¹ with 87.3% protein rejection while a thin-film membrane with a cut-off value of 4 kDa (TF4) operated at 26.3 L m⁻² h⁻¹ with 92.4% of protein rejection, allowing the free transmission of glucose. Large differences were measured between the distrubutions of various kinds of resistances for the PES5 and TF4 membranes; 65% of the total resistance was due to the fouling mechanism in the case of the PES5 membrane, whereas the fouling resistance amounted to only 41% for TF4 membrane. Ultrasound (US) treatment during the UF of a hydrolysate increased the flux and changed the proportions of fouling resistance and the gel resistance.

Keywords:

• Enzyme recovery
• Biofuels
• Cellulosic biomass
• Ultrasound
• Membrane separation

Acknowledgements

This work was supported by the European Union and co-funded by the European Social Fund. Project number: TÁMOP-4.2.2/B-10/1-2010-0012, “Broadening the knowledge base and supporting the long-term professional sustainability of the Research University Centre of Excellence at the University of Szeged by ensuring the rising generation of excellent scientists”. and project number: TÁMOP-4.2.1/B-09/1/KONV-2010-0005, “Creating the Center of Excellence at the University of Szeged” supported by the European Union and co-financed by the European Regional Fund”.

Notes

Presented at the Conference on Membranes in Drinking and Industrial Water Production Leeuwarden, The Netherlands, 10–12 September 2012. Organized by the European Desalination Society and Wetsus Centre for Sustainable Water Technology