RESEARCH ARTICLE Copyright © 2012 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Biobased Materials and Bioenergy Vol. 6, 1–7, 2012 Efficient Bioethanol Production from Glucose-Xylose Mixtures Using Co-Culture of Saccharomyces cerevisiae Immobilized on Canadian Pine Wood Chips and Free Pichia stipitis Ravi Dhabhai 1 2 ∗ , Satyendra P. Chaurasia 1 , and Ajay K. Dalai 2 1 Department of Chemical Engineering, Malaviya National Institute of Technology Jaipur, JLN Marg, Jaipur 302017, India 2 Catalysis and Chemical Engineering Laboratories, Department of Chemical and Biological Engineering, University of Saskatchewan, Saskatoon, SK S7N 5A9, Canada To meet the ever increasing demand for energy and fuels, it is essential to produce renewable fuels such as bioethanol at low cost and in reduced time. In the present work, Saccharomyces cerevisiae was immobilized on a novel Pinewood chips (PC) support and the immobilized yeast was used in fermentation with an aim to increase bioethanol yield and productivity in single and mixed sugar fermentation. Different concentrations of glucose or xylose were used to see the effect on ethanol production from S. cerevisiae and P. stipitis, separately. With PC immobilized S. cerevisiae, ethanol yield of 0.44 g/g and productivity of 1.11 g/l · h were obtained for 200 g/l initial glucose concentration. This immobilized S. cerevisiae, was then used in co-culture along with free culture of Pichia stipitis for ethanol production from glucose-xylose sugar mixtures (1.5:1 ratio of glucose to xylose; average concentration 50.75 g/l) and compared with co-culture of free S. cerevisiae and free P. stipitis. Improvement in ethanol yield (0.47 g/g from 0.45 g/g in case of co-culture of free cells) and productivity (0.73 g/h.h from 0.45 g/l · h in case of co-culture of free cells) were obtained with co-culture of immobilized S. cerevisiae and free P. stipitis. Further, PC were treated with a sequential treatment of H 2 SO 4 followed by sodium sulphite and sodium chlorite and used to immobilize S. cerevisiae. Yeast immobilized on treated pine wood chips support (TP) was then used in co-culture with free P. stipitis and further improvement in ethanol yield (0.50 g/g) and productivity (0.80 g/l · h) were obtained for 50.8 g/l initial glucose-xylose mixture concentration. This work showed that this novel co-culture scheme of S. cerevisiae immobilized on pine wood chips and free P. stipitis can be used for efficient fermentation of mixed sugars to bioethanol. Keywords: Bioethanol, Immobilization, Co-Culture, Fermentation, Pine Wood Chips, Saccharomyces cerevisiae. 1. INTRODUCTION Immobilization of yeasts offers advantages over free cell system in being efficient in terms of productivities and minimization of process costs. A good immobilization support material needs to meet several criteria like insol- ubility, mechanical stability, high diffusivity, simplicity of immobilization, superior surface characteristics like high surface area, pore volume and low cost. 1 Various materials have been used for immobilization such as Ca-alginate, k-carragenan gel, polyacrylamide, alumina, ∗ Author to whom correspondence should be addressed. Email: ravidhabhai08@gmail.com PVA gel, chitosan, cellulose, agar-agar, gluten pellets, spent grains, watermelon pieces, lignocellulose, and even microorganism in the form of yeast bio capsules. 2–9 Some of these materials are unsuitable for a range of microor- ganisms while some others are either not easily available and/or not cost effective. In order to make bioethanol process competitive, it is essential to produce ethanol at low cost and reduced fer- mentation time. It can be achieved by using immobi- lized yeast for ethanol production which facilitates faster fermentation rates by providing higher cell densities per unit fermentation volume. In addition, immobilization and the in situ removal of cells reduces the cost of recovery and repeated inoculum preparations and protects the cells J. Biobased Mater. Bioenergy 2012, Vol. 6, No. 5 1556-6560/2012/6/001/007 doi:10.1166/jbmb.2012.1253 1