Enzymatic hydrolysis of waste paper in an external loop airlift bubble column with continuous ultrasonic irradiation

The enzymatic hydrolysis of shredded office paper as a model of waste paper was carried out in an external loop airlift bubble column with continuous ultrasonic irradiation. The paper used was 6 x 12 mm in size and suspended much less easily compared to a microcrystalline cellulose powder of 35 to 65 mum in diameter. Oxygen in the sparging air exerted no inhibitory effect on the enzymatic hydrolysis and the location of a horn for ultrasonic irradiation in the downcomer was slightly more efficient than that in the riser to enhance the hydrolysis. Even in the case of no ultrasonic irradiation, the enzymatic hydrolysis in the airlift reactor proceeded as a two-stage process as opposed to that in the previous stirred tank reactor. 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. The enzymatic hydrolysis in the ultrasonic airlift reactor was enhanced by the gas-sparging as well as ultrasonic irradiation. As a result, the external loop airlift bubble column was found to be more advantageous for higher sugar concentrations compared to the stirred tank reactor. The time courses were kinetically analyzed and simulated based on the kinetic model proposed previously. It was shown that the ultimate sugar concentration increased with an increasing initial substrate concentration and ultrasonic intensity, and that the apparent kinetic constant increased with the intensity.