Agitation - Aeratio ' N in Submerged Fermentation

For the successful operation of aerobic fermentations it is essential to supply the microorganiisms with sufficient oxygen to meet their requirements at any stage in the process. Failure to supply enough oxygen may lead to undesirable changes in enzymatic makeup (Rolinson, 1952) or death of the organisms (Hromatka et al., 1951), with a subsequent lower yield of the desired product. In general, the supply of oxygen to bacterial cultures is more easily maintained than is the supply to submerged cultures of filamentous fungi. The extremely rigid (non-Newtonian) broths produced by filamentous fungi promote the coalescence of bubbles with consequent reduction in transfer area between the gas and liquid phases and alteration of turbulence and liquidfilm conditions. For example, Chain and Gualandi (1954) observed about 57 per cent reduction in the oxygen solution rate in the presence of 1.35 per cent dry weight of mycelium of Penicillium chrysogenum. Deindoerfer and Gaden (1955) reported a 100-fold increase in the rigidity of penicillin broth during the course of a fermentation in which about 1 per cent dry weight of mycelium was produced; a mycelial coIncentration of 1.34 per cent reduced the oxygen absorption rate by 85 per cent. Also, the addition of 0.25 per cent antifoam agent (3 per cent Alkaterge C in lard oil) reduced the oxygen absorption coefficient by 50 per cent. In studies using paper pulp to simulate mold mycelium, Bowers (1955) found that the addition of 2 per cent pulp reduced the oxygen solution rate given by a sintered aerator by a factor of 20; this was altered to a factor of 2 by high speed agitation (vaneddisc impeller) over an open-pipe sparger. Although the physical effects of mold mycelium on the oxygen absorption rate in submerged fermentations have been recognized, a study of the effects of mycelium concentration and morphology on the correlations between oxygen absorption coefficients and operating variables (air flow rate, agitator speed) seemed desirable. Hence studies were made on the effects of filamentous mycelium, paper pulp, and sago pellets