CONTROL OF PELLET MORPHOLOGY OF FILAMENTOUS FUNGI IN FLUIDIZED-BED BIOREACTORS BY MEANS OF A PULSING FLOW - APPLICATION TO ASPERGILLUS-NIGER AND PHANEROCHAETE-CHRYSOSPORIUM

The application of a pulsing flow to fluidized-bed bioreactors in orde r to control pellet morphology of filamentous fungi was investigated. The operation at an optimum pulsation frequency allowed two effects: a narrower pellet size distribution which improves fluidization quality , and an enhanced production of citric acid by Aspergillus niger and m anganese peroxidase by Phanerochaete chrysosporium. In the case of A. niger, the pellet diameter corresponding to rite pulsed system operate d at 0.35 s(-1) was kept between 3.3 +/- 0.1 mm after 22 days of opera tion; however, in the nonpulsed bioreactor which was operative for onl y If days, pellets with a diameter of 6.7 +/- 0.3 mm were produced. Si milar results were obtained in rite case of P. chrysosporium, since wi th a pulsing frequency of 0.0625 s(-1), a pellet diameter of 2.1 +/- 0 .4 mm after 34 days of operation was maintained. On the contrary, the system without pulsation presented great conglomerates of mycelia with an average diameter of 3 cm surrounded by free pellets with a diamete r distribution of 2.75 +/- 0.5 mm. The nonpulsed bioreactor was only o perative for 14 days. Both citric acid and manganese peroxidase produc tion attained higher values and were maintained longer in the pulsed b ioreactor.