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Aqueous-ammonia-steeped switchgrass was subject to simultaneous saccharification and fermentation (SSF) in two pilot-scale bioreactors (50- and 350-L working volume). Switchgrass was pretreated by soaking in ammonium hydroxide (30%) with solid to liquid ratio of 5 L ammonium hydroxide per kilogram dry switchgrass for 5 days in 75-L steeping vessels without agitation at ambient temperatures (15 to 33 degrees C). SSF of the pretreated biomass was carried out using Saccharomyces cerevisiae (D(5)A) at approximately 2% glucan and 77 filter paper units per gram cellulose enzyme loading (Spezyme CP). The 50-L fermentation was carried out aseptically, whereas the 350-L fermentation was semiaseptic. The percentage of maximum theoretical ethanol yields achieved was 73% in the 50-L reactor and 52-74% in the 350-L reactor due to the difference in asepsis. The 350-L fermentation was contaminated by acid-producing bacteria (lactic and acetic acid concentrations approaching 10 g/L), and this resulted in lower ethanol production. Despite this problem, the pilot-scale SSF of aqueous-ammonia-pretreated switchgrass has shown promising results similar to laboratory-scale experiments. This work demonstrates challenges in pilot-scale fermentations with material handling, aseptic conditions, and bacterial contamination for cellulosic fermentations to biofuels.

The objective of this study was to determine the effectiveness of different organic acids (maleic, succinic, and oxalic acid) on enzymatic hydrolysis and fermentation yields of wheat straw. It was also aimed to optimize the process conditions (temperature, acid concentration, and pretreatment time) by using response surface methodology (RSM). In line with this objective, the wheat straw samples were pretreated at three different temperatures (170, 190, and 210°C), acid concentrations (1%, 3%, and 5%) and pretreatment time (10, 20, and 30 min). The findings show that at extreme pretreatment conditions, xylose was solubilized in liquid phase, causing an increase in cellulose and lignin content of biomass. Enzymatic hydrolysis experiments revealed that maleic and oxalic acids were quite effective at achieving high sugar yields (>90%) from wheat straw. In contrast, the highest sugar yields were 50-60%, when the samples were pretreated with succinic acid, indicating that succinic acid was not as effective. The optimum process conditions for maleic acid were, 210°C, 1.08% acid concentration, and 19.8 min; for succinic acid 210°C, 5% acid concentration, and 30 min; for oxalic acid 210°C, 3.6% acid concentration, and 16.3 min. The ethanol yields obtained at optimum conditions were 80, 79, and 59% for maleic, oxalic and succinic acid, respectively. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1487-1493, 2016 [ABSTRACT FROM AUTHOR]

Growth curves are used in a wide range of applications such as crop science and biotechnology. Besides, mathematical models for fermentation can provide more information about kinetic of cell growth, and also promote the control and optimization of cell growth during fermentation. The main objectives of this study were undertaken not only plotted the cell growth curves, determined the specific growth equations, and calculated the kinetic parameters belong to Scheffersomyces stipitis strains (ATCC 58784 and 58785) but also to modelled their cell growths by using modified logistic and modified Richards models. The results indicated that the specific growth curves of ATCC 58784 in glucose and xylose mediums were y=0.3047×Abs600-0.2656 and y=0.2322×Abs600+0.4329, respectively. For ATCC 58785, they were y=0.2639×Abs600+0.0282 and y=0.2323×Abs600+0.6211, respectively. Furthermore, for ATCC 58784, maximum growth rate and doubling time values in glucose and xylose media were 0.23, 0.11 g/L/h and 2.45, 8.58 h, respectively. For ATCC 58785, they were 0.33, 0.11 g/L/h and 2.51, 7.66 h, respectively. In addition, modified logistic and modified Richards models were tested in order to describe cell growth profiles during fermentation by S. stipitis strains. Results indicated that these models can serve as a universal equation to fit cell growth. Moreover, validation of these models demonstrated that cell growth was all predicted accurately (slope=0.96 and 0.97, R2=0.998 and 0.998 for ATCC 58784 in xylose media by modified logistic and modified Richards models, respectively; slope=1.01 and 1.01, R2=0.995 and 0.995 for ATCC 58785 in xylose media by modified logistic and modified Richards models, respectively). [ABSTRACT FROM AUTHOR]

Background: Improvement of biofeedstock quality for cellulosic ethanol production will be facilitated by inexpensive and rapid methods of evaluation, such as those already employed in the field of ruminant nutrition. Our objective was to evaluate whether forage quality and compositional measurements could be used to estimate ethanol yield of maize stover as measured by a simplified pretreatment and simultaneous saccharification and fermentation assay. Twelve maize varieties selected to be diverse for stover digestibility and composition were evaluated. Results: Variation in ethanol yield was driven by glucan convertibility rather than by glucan content. Convertibility was highly correlated with ruminal digestibility and lignin content. There was no relationship between structural carbohydrate content (glucan and neutral detergent fiber) and ethanol yield. However, when these variables were included in multiple regression equations including convertibility or neutral detergent fiber digestibility, their partial regression coefficients were significant and positive. A regression model including both neutral detergent fiber and its ruminal digestibility explained 95% of the variation in ethanol yield. Conclusion: Forage quality and composition measurements may be used to predict cellulosic ethanol yield to guide biofeedstock improvement through agronomic research and plant breeding. [ABSTRACT FROM AUTHOR]