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Data reported here and previously indicate that when dextrin is hydrolyzed in the presence of immobilized glucoamylase, use of a larger average molecular weight substrate leads to lower overall rates of hydrolysis, while the maltose concentration during the bulk of the reaction and the maximum glucose concentration are lower than when the soluble form of the enzyme is employed under the same conditions. Computer simulation of the system demonstrated that all three observations were caused by pore diffusion limitation: the first by slow diffusion of substrate, the second by slow diffusion of intermediates, and the third by slow diffusion of glucose. Follow-up experiments with glucoamylase immobilized to particles of different sizes confirmed this finding, as results with the smallest beads were identical to those with soluble glucoamylase.
The rate of biological processes in aerobic fermentation and waste water treatment is often limited by the rate of dissolution of oxygen from air bubbles into the liquid. A clear understanding of interfacial resistance to oxygen transfer is thus of importance. An oxygen sensing microprobe was used to detect a stagnant film and a penetrable zone near an air-water interface contaminated with surfactants. The technique, when used in clean water, can also measure the frequency of surface renewal. A linear relationship was found between the square root of the renewal rate sO.5 and the interfacial mass transfer coefficient kL, which is predicted by the Danckwerts theory.
SCOPEwas stirred with the agitator at different speeds (revolutions per miniite marked in Figure 3), the signals (reflecting local oxygen concentration) were found to fluctuate at different frequencies. Each of the abrupt changes on the recorder curves was interpreted to reflect a renewal of the surface with R liquid element freshly brought to the interfacial zone by the agitator. By counting the fluctiiation frequency 011 the recorder charts, it was possible to obtain n linear correlation between k~. and 80.5, shown in Figure 4. This linear correlation agrees with Danckwerts's surface renewal equation ICL = (D S)O.5 and provides a direct experimental support to the Danckwerts theory.
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