Host: The Society of Chemical Engineers, Japan
The office paper shredded into various sizes was used as a model substrate of waste paper in this work. The enzymatic hydrolysis of the office paper was carried out in an external airlift bubble column reactor equipped with an ultrasonic horn system with sparging the water saturated or unsaturated gas. The sparging gas humidity, substrate size and ultrasonic intensity were varied to examine their respective effects on the enzymatic reaction. The enhanced hydrolysis showing a two-stage time course was observed even with no ultrasonic irradiation in the airlift reactor when either unsaturated air or nitrogen was bubbled into the reaction suspension, while much less enhancement effect was observed when either saturated air or nitrogen was employed. The total sugar productivity with sparging either saturated air or nitrogen was lower than that in the case of sparging unsaturated gas. This was ascribed to a shear stress acting on the surface of office paper in the gas-sparging section in the riser in the same way as in the ultrasonic irradiation section in the stirred tank used previously. The critical superficial gas velocity for the complete substrate circulation was found to be reduced as the substrate size decreased. The smaller paper size required the lower critical gas velocity in addition to a more enhanced hydrolysis with a more remarkable two-stage time course. In the ultrasonic airlift reactor with sparging the saturated air, the continuous ultrasonic irradiation was also found to be effective for enhancing the enzymatic hydrolysis. The time courses observed were analyzed and simulated successfully based on the kinetic model proposed previously. The variation in the paper sizes, sparging gas humidity and ultrasonic irradiation exerted an effect on the apparent rate constant and ultimate total sugar concentration, but no effect on the apparent Michaelis and competitive inhibition constants.
