ENZYMATIC HYDROLYSIS OF LIGNOCELLULOSIC MATERIALS (ANAEROBIC FERMENTATION, DESORPTION, ADSORPTION, RATE AND EXTENT, SURFACE CHARACTERIZATION, MASS TRANSPORT)

The major factors governing rate and extent of enzymatic hydrolysis of natural lignocellulosic materials (corn stover, CST; and wheat straw, WST) as a function of particle size, and limiting factors in the engineering application of the process were studied.; With enzymatic hydrolysis, an observed fast initial carbohydrate solubilization rate was followed by a rapid decline to stoppage within about 48 hours. The rate was not influenced either by external or internal mass transfer limitation for the particle sizes studies, therefore reflecting the intrinsic enzymatic behavior on the lignocellulosic particle surface. For both lignocellulosic materials, initial rates of hydrolysis were found to increase with decrease in particle size. The extent of holocellulose hydrolysis was only about 40% for CST and 12 to 25% for WST.; The enzyme system was adsorbed both reversibly and irreversibly within a few minutes to CST and WST, as well as to the lignaceous materials studied, reflecting both productive as well as nonproductive adsorption. The adsorption "isotherms" of the activity producing glucose from BW200 cellulose could be adequately modeled either by Freundlich- or Langmuir-type adsorption models, even though the adsorption appeared largely irreversible within the time frames tested.; The surface process was characterized by a biphasic behavior. The substrate was hypothesized to consist of a delaminated outer layer that was readily hydrolyzed and a dense, difficult to hydrolyze, inner core. The rate of hydrolysis was more a function of the relative ease of enzymatic cleavage of different holocellulose bonds within a given material than of the total holocellulose concentrations remaining, thus making Michaelis-Menten kinetics inadequate for describing the process.; The observed behavior of the soluble enzyme system was found to be in sharp contrast to that of an anaerobic mixed microbial population which showed a rather slow but complete holocellulose solubilization with both lignocellulosic materials studied. Several factors might explain this behavior, the most important of which appears to be the different adsorption behavior, enzyme induction, growth, and proteolytic activity of the mixed anaerobic microbial population. The experimental results are likely to be applicable to the development and design of processes leading to the production of renewable forms of energy and chemicals.