Pressure pulsation in solid-phase fermentation

Inadequate dissipation of heat generated by biologic activities has prevented the use of solid-phase fermentation in large-scale applications. This study deals with the cooling effects of pressure pulsation on solid, porous beds. Pressure pulsation also enhances evaporation of medium moisture, which is also described. Computer software has been developed for on-line control of heat accumulation and moisture loss involving automatic variation in pressure pulsation frequency and airflow direction as well as replenishment of water. Aspergillus niger NRRL3 was cultivated on a moist, solid medium made of wheat bran and ground corncobs to produce cellobiase. During 100h of fermentation, the maximum temperature inside the solid bed was kept under 40°C, and the medium water content was successfully maintained between 61 and 65%, which was optimal for cell growth. Cells grew heavily on the solid-phase substrate and distributed uniformly. With good on-line control of temperature and moisture, the 12-L fermentor provided a better environment for enzyme production than 250 mL flasks did.