Douglas G. Macdonald

Recycle Bioreactor for Bioethanol Production from Wheat Starch II. Fermentation and Economics

Bioethanol has been produced using sugars from cold hydolysis of pure wheat starch, sterile wheat flour, and unsterile wheat flour. The conversion of sugars to ethanol from pure starch reached 96% of the theoretical maximum while that from sterile wheat flour was 69% and from unsterile wheat flour only 35%. These data indicate that sequential hydrolysis and fermentation of wheat flour is not feasible. However, the simultaneous cold hydrolysis and fermentation of both wheat starch and wheat flour proved successful. Both sugar sources produced 95% of the theoretical maximum amount of ethanol. The process could be repeated in a sequential batch fashion for over 110 h of operation, achieving high ethanol yields in each run. A scale-up design of bioethanol production using sequential batch, simultaneous cold starch hydrolysis, and fermentation indicates that this process would be economically feasible. High levels of revenue are generated from both the bioethanol and the byproduct: food-grade wheat gluten. The...Bioethanol has been produced using sugars from cold hydolysis of pure wheat starch, sterile wheat flour, and unsterile wheat flour. The conversion of sugars to ethanol from pure starch reached 96% of the theoretical maximum while that from sterile wheat flour was 69% and from unsterile wheat flour only 35%. These data indicate that sequential hydrolysis and fermentation of wheat flour is not feasible. However, the simultaneous cold hydrolysis and fermentation of both wheat starch and wheat flour proved successful. Both sugar sources produced 95% of the theoretical maximum amount of ethanol. The process could be repeated in a sequential batch fashion for over 110 h of operation, achieving high ethanol yields in each run. A scale-up design of bioethanol production using sequential batch, simultaneous cold starch hydrolysis, and fermentation indicates that this process would be economically feasible. High levels of revenue are generated from both the bioethanol and the byproduct: food-grade wheat gluten. The payback period is predicted to be < 2 years with a discounted cash flow rate of return of 46%.

a-Amylase inhibition and inactivation in barley malt during cold starch hydrolysis

Abstracta-Amylase from barley malt decayed at a rate of 1.1% h at 45°C and this decay rate was greatly accelerated at 55°C. Glucose and maltose inhibited the catalytic actions of both bacterial and barley a-amylase in the same manner during the hydrolysis of starch granules. The catalytic activity dropped exponentially as these sugars increased up to 400 g/L; with about 50% activity at 100 g/L. Equations are presented to model both time decay of the enzyme and the inhibition effect of the sugars.

Recycle Bioreactor for Bioethanol Production from Wheat Starch I. Cold Enzyme Hydrolysis

A 5 L membrane bioreactor system has been designed and operated at low temperature to hydrolyze starch granules directly to sugars using barley ¬-amylase. The system includes a temperature and pH controlled, well-mixed bioreactor; microWlters to separate and recycle granules; and ultraWlters to separate and recycle enzyme molecules. Operation in batch mode demonstrated similar kinetics and low productivity observed earlier in shake Xasks, whereas continuous Xow operation was not successful due to enzyme inhibition and degradation. Sequential batch mode operation, involving Wltration after each batch hydrolysis, produced optimum productivity measured at 0.16 grams of starch granules hydrolyzed per gram of enzyme per hour for more than 100 hours of operation.A 5 L membrane bioreactor system has been designed and operated at low temperature to hydrolyze starch granules directly to sugars using barley α-amylase. The system includes a temperature and pH controlled, well-mixed bioreactor; microfilters to separate and recycle granules; and ultrafilters to separate and recycle enzyme molecules. Operation in batch mode demonstrated similar kinetics and low productivity observed earlier in shake flasks, whereas continuous flow operation was not successful due to enzyme inhibition and degradation. Sequential batch mode operation, involving filtration after each batch hydrolysis, produced optimum productivity measured at 0.16 grams of starch granules hydrolyzed per gram of enzyme per hour for more than 100 hours of operation.

FERMENTATION OF CHEESE WHEY IN AN IMMOBILIZED-CELL FLUIDIZED-BED REACTOR

ABSTRACT Batch and continuous fermentation of cheese whey to lactic acid were carried out in a fluidized bed reactor by using Lactobacillus bulgaricus immobilized in 3% (w/v)garose. Five batch fermentations conducted under uncontrolled pH conditions and initial lactose concentrations ranging from 40 to 60g/L gave an average final lactic acid concentration of 6·9 g/L in a 48 to 50 h period. Continuous fermentation under controlled pH conditions at four different dilution rates ranging from 0·043 to 0·428 h-1 and a lactose inlet concentration of 43·5 g/L resulted in a lactic acid yield of 0·26mg/mg lactose consumed. The maximum lactic acid concentration was 10·0 mg/mL at a dilution rate of 0·086 h-1 with a substrate utilization of 90·5∥. The mathematical model of the system for batch and continuous operations was developed and the model parameters were determined experimentally and by non-linear multiple regression analysis.

KINETIC STUDIES OF WHEAT STRAW HYDROLYSIS USING SULPHURIC ACID

The kinetics of cellulose and hemicellulose hydrolysis of wheat straw were studied using both isothermal and non-isothermal techniques in a batch reactor. Reactions were carried out between 100 and 210°C and product sugars were analyzed using a Bio-Rad HPX-87P liquid chromatographic column. A simple first order series reaction model was used for both cellulose and hemicellulose hydrolysis reactions and kinetic parameters were obtained for the Arrhenius rate equations for three different sulphuric acid concentrations (0.5, 1.0 and 1.5%). Activation energies remained constant with acid concentration but the pre-exponential factors showed an increase with acid concentration. To minimize the amount of experimental data required and to achieve a unique solution to the kinetic parameters, the technique of combining isothermal and non-isothermal reaction data was studied.