Towards Fed-batch Enzymatic Hydrolysis of Lignocellulosic Biomass for Bioethanol Production

Domestic biofuels production has not been cost-competitive with petroleum due to a high cost of enzyme and energy consumption during conversion of feedstocks into biofuels. Fed-batch enzymatic hydrolysis was studied to accumulate high concentration of sugars with maximum possible biomass conversion. The research presented in this dissertation begins with the establishment of dilute sulfuric acid pretreatment conditions under moderate temperatures, followed by enzyme adsorption and glucan conversion profile studies in batch enzymatic hydrolysis. An epidemic based mathematical model was developed to describe the enzymatic hydrolysis of dilute acid pretreated biomass. The process of substrate being adsorbed and digested by enzyme was simulated as susceptibles being infected by viruses and then becoming removed and recovered. The model was extended to fed-batch hydrolysis with the consideration of a system volume change and the negative effect of accumulated lignin. An optimal mathematical control strategy for the feeding operation was developed with an objective function of maximizing cellulose conversion during processing and glucose concentration at the final time of processing. Practical boundary conditions such as feeding rate and lignin content were established for feasible controls and current hydrolysis system. The solids content in the feeding source had a significant influence on the balance of feeding pressure on system mass transfer and the digested glucose concentration. Consequently, a fuzzy logic feedback control system was developed for process monitoring and feeding control during fed-batch enzymatic hydrolysis. Digested glucose from the hydrolysis reaction was assigned as an input (antecedent) while doser feeding times and rates of biomass addition were responses (consequences) for the fuzzy logic control system. The control between the feeding of a proper amount of cellulose and maintenance of solids content was well balanced during each operational decision. Both optimal control strategy and fuzzy logic feeding control proved to be robust and effective tools for fed-batch enzymatic hydrolysis, which could be a great improvement towards industrialization of advanced biofuels