Abstract
In this study, a modified bubble column with rectangular wire-mesh draft tubes was developed. In the proposed fermentor, air bubbles were dispersed from the air sparger into the inner section of the draft tubes and bubbles flowed upward along the duct of draft tubes. Some bubbles were broken by colliding against the wires and passed through the wire meshes. The draft tubes provided additional mechanism that decreased the bubble coalescence and broke the bubbles in the fermentor. Gas holdup (ε), volumetric oxygen transfer coefficient (kLa), and mixing time were employed for evaluating the performance of the proposed fermentor using the air-water system with different number of wire-mesh draft tubes in two different scales of columns. Both columns, 13 and 29 cm in diameter and 200 cm in height, were made of transparent perspex. The experimental results showed thatεand kLa increased up to 90% and 50%; the mixing time reduced up to 30% in comparison with those of the conventional bubble column. The correlation equations of εand kLa with respect to superficial air velocity (Ug) and the characteristic surface area of the draft tubes (Ac) were expressed as :ε=12.51 Ug^1.333 Ac^0.044, 0.01<Ug<0.05 m/s 0.71 Ug^0.421 Ac^0.086, 0.01<Ug<0.05 m/skLa=0.744 Ug^0.827 Ac^0.113, 0.01<Ug<0.05 m/s 0.141 Ug^0.327 Ac^0.148, 0.01<Ug<0.05 m/sTwo different scales of fermentors were also constructed according the dimensions of the perspex columns, and applied to submerged culture of Monascus.The submerged culture of Monascus purpureus for pigment production was investigated. The microorganisms were Monascus purpureus CCRC 38038. Rice grain and monosodium glutamate (MSG) were the main carbon and nitrogen sources.Different treatments of rice grain for rice substrate preparations were employed. The treatments of rice grain changed the rheological characteristics of culture medium that affected the performance of culture. Rice powder was not a good substrate because of serious foaming under aeration and gelatinization after sterilization. Suspended rice particles in liquid medium was suitable for submerged culture of Monascus.The optimal medium composition was obtained by using the response surface method (RSM) in the ranges of rice grain between 2 and 3%, and MSG between 3 and 4%. Higher initial concentration of rice grain was not suitable for the pigment production. Fed-batch culture was carried out with a feeding strategy that the amount of rice particles was maintained at lower level during the cultivation. The pigment production in the fed-batch culture increased about 100% in comparison with that in bath culture with the same amounts of rice grain (4%) and MSG (3%).Batch and fed-batch culture experiments were conducted in the lab-scale fermentor. Pigment production in the lab-scale fermentor was closed to that in the shake flask. Furthermore, an automatic feeding strategy based on pH value as an indicator was developed. The result showed that the cultivation time was shortened in 24 hrs by using the automatic feeding strategy.The cultivation of M. purpureus in the pilot-scale fermentor was also successfully carried out in pigment production based on the criterion of maintaining the constant value of kLa. Thus, a submerged culture of M. purpureus for production of monascus pigment from shake flask to pilot-scale fermentor has been developed in this dissertation.