Ethanol Production From Glucose and Dilute-Acid Hydrolyzates by Encapsulated S. cerevisiae Farid Talebnia, 1,2 Claes Niklasson, 1 Mohammad J. Taherzadeh 2 1 Department of Chemical Engineering and Environmental Science, Chalmers University of Technology, 412 96 Go ¨teborg, Sweden; telephone: +46 33 435 4429; fax: +46 31 772 30 35; e-mail: talebnia @chemeng.chalmers.se 2 School of Engineering, University College of Bora ˚s, 501 90 Bora ˚s, Sweden Received 13 May 2004; accepted 6 December 2004 Published online 16 March 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/bit.20432 Abstract: The performance of encapsulated Saccharomy- ces cerevisiae CBS 8066 in anaerobic cultivation of glucose, in the presence and absence of furfural as well as in dilute-acid hydrolyzates, was investigated. The cultivation of encapsulated cells in 10 sequential batches in synthetic media resulted in linear increase of biomass up to 106 g/L of capsule volume, while the ethanol produc- tivity remained constant at 5.15 (F0.17) g/LÁh (for batches 6–10). The cells had average ethanol and glycerol yields of 0.464 and 0.056 g/g in these 10 batches. Addition of 5 g/L furfural decreased the ethanol produc- tivity to a value of 1.31 (F0.10) g/LÁh with the encapsu- lated cells, but it was stable in this range for five consecutive batches. On the other hand, the furfural decreased the ethanol yield to 0.41–0.42 g/g and in- creased the yield of acetic acid drastically up to 0.068 g/g. No significant lag phase was observed in any of these experiments. The encapsulated cells were also used to cultivate two different types of dilute-acid hydrolyzates. While the free cells were not able to ferment the hydro- lyzates within at least 24 h, the encapsulated yeast suc- cessfully converted glucose and mannose in both of the hydrolyzates in less than 10 h with no significant lag phase. However, since the hydrolyzates were too toxic, the encapsulated cells lost their activity gradually in sequential batches. B 2005 Wiley Periodicals, Inc. Keywords: encapsulation; dilute-acid hydrolyzate; furfural; Saccharomyces cerevisiae; alginate; ethanol INTRODUCTION Fuel ethanol is nowadays a substitute for, as well as additive to, the traditional fossil fuels. Among the different resources used for ethanol production, lignocellulosic materials are the most abundant ones, and they are usually available at low cost. These materials could be processed to the sugar monomers by acid and/or enzymatic hydrolysis followed by fermentation of the sugars to ethanol. Acid hydrolysis is a fast and relatively cheap method for ac- quiring sugars from lignocelluloses, while enzymatic hydrolysis as well as fermentation usually take long times. On the other hand, acid hydrolysis has the drawback of producing some inhibitors that reduce the fermentability of the resultant hydrolyzates (Luo et al., 2002; Taherzadeh et al., 1997). These inhibitors are furans, phenolic com- pounds, and carboxylic acids (Clark and Mackie, 1984). Furfural and hydroxymethylfurfural (HMF) are known as two of the strongest inhibitor compounds present in the hydrolyzate. Taherzadeh et al. (1997) found a clear relationship between specific ethanol production rate by Saccharomyces cerevisiae in dilute-acid hydrolyzate and the sum of furfural and HMF concentrations. Higher con- centrations of furfural and HMF resulted in less fer- mentability of the hydrolyzates. Banerjee et al. (1981) have shown that furfural at a concentration of 4 g/L inhibited the growth of S. cerevisiae and alcohol production by 80% and 97%, respectively. High cell concentration in the cultivation media can help decreasing the fermentation time as well as increasing the tolerance of the cells against the inhibitors (Chung and Lee, 1985; Galazzo and Bailey, 1990). Immobilization of the cells in alginate has successfully been applied to achieve these goals (Taherzadeh et al., 2001). Among the different methods of immobilization, cell encapsulation is a prom- ising method that probably has advantages over conven- tional immobilizing methods (Chang et al., 1996; Park and Chang, 2000). In this method, cells are confined in a semipermeable, spherical, and thin membrane. Due to the absence of a solid or gelled core and small wall diameter, mass transfer resistance is less than that of the entrapment methods. The membrane of the capsule should be designed such that the required nutrients and cell products can easily pass through it (Groboillot et al., 1994; Jen et al., 1996). Encapsulation can be carried out by using either natural or synthetic polymers such as calcium alginate (Cheong et al., B 2005 Wiley Periodicals, Inc. Correspondence to: F. Talebnia Contract grant sponsor: Swedish National Energy Administration (STEM)