Boutros Fouad Sarrouh

Biotechnological production of xylitol in a three-phase fluidized bed bioreactor with immobilized yeast cells in Ca-alginate beads

Cells of Candida guilliermondii entrapped in Ca‐alginate beads were used for xylitol production, from concentrated hemicellulose hydrolyzate of sugarcane bagasse, in a fluidized bed bioreactor (FBR). The maximum xylitol concentration 28.9 g xylitol/L was obtained at a high aeration rate of 600 mL/min after 70 h of fermentation, indicating that the use of high aeration rate in this system is favored for better oxygen transfer into the immobilized cells. The specific xylitol productivity and the xylitol yield were of 0.4 g xylitol/L.h and 0.58 g xylitol/g xylose respectively. The immobilization efficiency at the end of the fermentation was of 65 %. After 90 h of fermentation xylitol productivity and yield decreased to 0.25 g xylitol/L.h and 0.47 g xylitol/g xylose respectively, indicating the beginning of xylitol consumption by the yeast. The use of FBR system with immobilized cells presented high xylitol yield and productivity.

Evaluation of the Performance of a Three-Phase Fluidized Bed Reactor with Immobilized Yeast Cells for the Biotechnological Production of Xylitol

This work deals with the evaluation of the hydrodynamic characteristics and fermentation parameters of a bench-scale three-phase fluidized bed reactor (FBR) with cells of the yeast Candida guilliermondii immobilized calcium alginate beads for xylitol production. The effects of the following hydrodynamic variables on cell immobilization were evaluated: total particle density, terminal velocity, particles drag force, minimum fluidization velocity and bed porosity (?). According to the results obtained, the reactor was shown to operate similar to a fixed-bed bioreactor at ? < 0.5 and a fluidized bed bioreactor at ? > 0.5, respectively. The maximum flowrate needed to obtain maximum bed fluidization in the reactor was equal to the terminal velocity of the immobilized cell particles. As for the fermentation parameters, the effects of the aeration rate and fermentation time on the process productivity and yield were analyzed. The maximum xylitol concentration of 28.9 g xylitol/l was obtained at a high aeration rate of 600ml/min after 70h of fermentation, indicating that the use of a high aeration rate in this system is favored for better oxygen transfer into the immobilized cells. The specific xylitol productivity and the xylitol yield were of 0.41 g xylitol/l.h and 0.582 g xylitol/g xylose respectively. After 90h of fermentation xylitol productivity and yield decreased to 0.256 g xylitol/l.h and 0.47 g xylitol/g xylose respectively, indicating the beginning of xylitol consumption by the yeast.

An Evaluation of Different Bioreactor Configurations with Immobilized Yeast for Bioethanol Production

The bioethanol industry expects a huge expansion and new technologies are being implemented with the aim of optimizing the fermentation process. The behavior of cells of Saccharomyces cerevisiae immobilized in PVA-LentiKats, during the production of bioethanol in two reactor systems, was studied. The entrapped cell in LentiKats lenses showed a different profile using stirred tank reactor (STR) and packed column reactor (PCR). Low free cells accumulation in the medium was observed for the STR after 72 h of fermentation. On the other hand, no free cells accumulation was observed, probably due to the absence of mechanical agitation in PCR configuration. Better fermentation results were obtained working with STR (final cellular concentration = 13 g.L-1, Pf = 28 g.L-1, Qp = 1.17 g.L-1.h-1,and Yp/s = 0.3 g.g-1) in comparison to PCR (final cellular concentration = 11.4 g.L-1, Pf = 20 g.L-1, Qp = 0.83 g.L-1.h-1,and Yp/s = 0.25 g.g-1). Such results are probably due to the mechanical agitation of the medium provided by STR configuration, which permitted a better heat and mass transference.

Production of cellulolytic enzymes by anaerobic fungi cultivated in different conditions.

The present paper studies the influence of different nutrients for the production of two cellulolytic enzymes: endo beta-1.4 glucanase and exo beta- 1.4 glucanase by anaerobic fungi taken from cow rumen, that were fed a diet of corn silage and Brachiaria decumbens grass hay. During the enzymatic degradation assays, it was observed that the addition of some essential nutrients in the formulation of the culture medium contributed positively in the cellulolytic enzyme production, with exception of riboflavin. Such results contributed in the establishment of an effective method for the evaluation of enzymatic activities in anaerobic fibrolytic fungi. In this work, nutrients added to enrich the culture medium have successfully proven that they can be used as inoculating agents (inductors) in diets rich in ensilage with law nutritive value.

Potential Biomass Resources for Cellulosic Ethanol Production in Brazil: Availability, Feedstock Analysis, Feedstock Composition, and Conversion Yields

Due to economic, geopolitical, and environmental issues, the world’s attention turns to alternative energy sources, especially for second-generation ethanol. In addition to economic considerations, other factors such as energy security, greenhouse gas emissions, and global climate change are boosting scientific researches concerning alternative bioenergy. According to the literature projections, more than 10 % of all gasoline used in the world can be replaced by biofuels over the next 15–20 years. Currently, Brazil is faced with the prospect of a significant increase in demand for ethanol. This prediction holds up in some market realities, as increasing domestic consumption of hydrous ethanol by the successful introduction of the alternative flex fuel vehicle market in automotive lightweight and expansion of Brazilian ethanol exports due to the increasing global interest in mixing alcohol with gasoline. In this context, all the potential sources for ethanol production must be considered wherein cellulosics stands out as an important alternative. In this chapter, we discuss about the potential to produce ethanol from lignocellulosic materials, a renewable source largely available in the world. Particularly, some aspects of potential sources in Brazil are described. First, however, brief comments on the composition of these materials and some analytical methods used to characterize them are exposed.