Although nowell-adjusted model could be evaborated from the experimental data to mathematically explain the mechanism of the iturin A production, using the DOE technique did lead to a positive conclusion on the technical feasibility of the proposed process by successful identification of operating conditions that resulted in high productivity by studying different conditions of operating parameters with a statistically controlled variation. These conditions were found for the combination of levels 1(0.46 L/min) of air flow rate and 1 (22.9%w/w) of rice husk. At the lower level conditions, less oxygen is available to the ferment due to both the lower air flow rate and the reduced porosity of the packed bed as a result of the lower ratio of rice husk compared to soy bean meal and wheat bran. According to Phae andShoda,1991 a lower aeration rate favors a higher production of iturin A and Khan etal.(2012) also found that a small but steady supply of
oxygen improves the production of iturin, since Bacillus is a facultative aerobic microorganism. On the other hand, the bulking agent was important operationally to reduce the pressure drop and allow air flow distribution across the packed bed.