Evaluation of oxygen mass transfer in fungal fermentation using airlift/bubble column bioreactors

Date
2013-12
Authors
Wong, Matthew K.
Journal Title
Journal ISSN
Volume Title
Publisher
[Honolulu] : [University of Hawaii at Manoa], [December 2013]
Abstract
Submerged fungal fermentation using bubble column and airlift bioreactors was investigated for converting bioethanol liquid waste, vinasse into high-value fungal protein for fish or animal feed applications. Previous studies suggested that fungal biomass yields are dependent on many environmental parameters such as: pH, nutrients, temperature, aeration rate, and colony morphology among others. There is a lack of studies that examine the oxygen mass transfer in fungal fermentation. This research closely examined the air-to-liquid oxygen mass transfer coefficient, kLa; an important factor affecting fungal biomass yield. Laboratory-scale, 2.5 L working volume bubble column and airlift bioreactors with sugarcane ethanol process derived vinasse as a substrate and the fungal species Rhizopus microsporus var. oligosporus were used for oxygen mass transfer studies. Results showed that kLa followed a power curve for both airlift and bubble column configurations using water-only media for air flow rates ranging from 0.5 to 2.0 volume of air/volume of liquid/minute (vvm). Power regression equations kLaALR = 37.9*vvm^0.949 and kLaBLR = 39.0*vvm^0.941 correspond to airlift and bubble column configurations, respectively.We determined that kLa for vinasse media alone (i.e., without fungus), increased for increasing aeration rates as expected for the bubble column configuration from 10.1 ±0.2 h-1 to 59.4 ±1.9 h-1, respectively at aeration rates of 0.5 to 3.0 vvm. The kLa for vinasse media was on average 34.1±17.7 % lower than water at each aeration rate when operated without fungus. Results showed that the presence of fungi in vinasse media resulted in decreases and increases of kLa compared to vinasse alone at 1.5 vvm. A maximum biological enhancement of +30.7% at 6.53 g was observed. Knowledge of the oxygen mass transfer properties in complex media fermentation is crucial for process scale-up and commercialization of the fungal technology.
Description
M.S. University of Hawaii at Manoa 2013.
Includes bibliographical references.
Keywords
Biofuel, fungal fermentation, oxygen mass transfer, airlift/bubble column bioreactors, volumetric mass transfer coefficient (kLa), vinasse
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