Ethanol production in biofilm reactor via repeated-batch fermentation using carob pod extract

Use of lignocellulosic materials and agricultural wastes/products in biotechnological processes has recently increased due to these resources have high sugar content. Accordingly, production of high value added products such as enzyme, organic acid, biofuel is important from the point of economy. In this study, repeated-batch fermentation was evaluated using a biofilm reactor for ethanol production from carob pod extract by Saccharomyces cerevisiae. Primarily, biofilm material was determined to provide for attachment on surface of yeast and then optimization of ethanol production from carob pod extract was performed at optimum conditions of response surface method. Thus, the effect of different combinations of nitrogen sources on fermentation was evaluated at optimum conditions determined. Besides, ethanol fermentation was carried out under optimum conditions in non-enrichment medium as control. Nevertheless, the ethanol fermentations were performed using non-sterile enrichment and non-enrichment medium and their effect on fermentation was investigated. Plastic Composite Support (PCS) material that causing biofilm formation providing on surface attachment of yeast in biofilm reactor was used. In order to determine the best biofilm material, four different PCS materials were used as following SH-SF-YE-SALTS, SH-SF-YE-BA-SALTS, SH-SF-SALTS and SH-SF-YE-RBC-SALTS. The highest ethanol production was obtained from biofilm material including SH-SF-YE-BA-SALTS. Then, selected PCS material was bonded on shaft in bioreactor and biofilm formation was performed to establish on PCS material. After optimization of ethanol production from carob pod extract was performed at conditions of response surface method. These conditions were selected as initial sugar concentration (4, 7 and 10ºBx), pH (5.0, 5.5 and 6.0) and agitation (100, 150 and 200 rpm). Optimum conditions were found to be 7.71ºBx, 5.18 pH and 120 rpm after fermentations. At the end of the determination optimum conditions, the effect of different combinations of nitrogen sources on fermentation in optimum conditions was researched. Consequently, the kinetic parameters such as yield, maximum consumption rate and maximum production rate of nitrogen sources were determined to be significantly important impact. Besides, ethanol fermentations in biofilm reactor were carried out in sterile non-enrichment (control), non-sterile enrichment and non-enrichment medium. Results showed that obtained yields and production rates were lower then optimum conditions scored. Overall, this study demonstrated that ethanol productions in a biofilm reactor from carob pod extract using Saccharomyces cerevisiae can be successfully implemented. Product yield and productivity were increased due to high cell concentration in biofilm reactor and biofilms attachment on PCS surface and fermentation time was determined as 12 hours. KEYWORDS: Carob pod extract, ethanol, biofilm reactor, repeated-batch fermentation, response surface method