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Model analysis of biological oxygen transfer enhancement in surface‐aerated bioreactors
Author(s) -
Ju LuKwang,
Sundarajan Anand
Publication year - 1992
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.260401108
Subject(s) - oxygen , aeration , bioreactor , chemistry , pulmonary surfactant , adsorption , chemical engineering , chromatography , limiting oxygen concentration , mass transfer , activated sludge , biochemistry , environmental engineering , organic chemistry , sewage treatment , engineering
Abstract A model was developed to evaluate the effects of cells and surfactants on oxygen transfer in surface‐aerated bioreactors. The model assumed the presence of serial layers of adsorbed surfactants and microorganisms directly adjacent to the gas–liquid interface due to their surface activities, followed by a stagnant liquid layer to account for the oxygen transfer resistance in the liquid phase. The interfacial surfactant film, although posing as an additional resistance, was found to have negligible effect on the oxygen transfer rate because of its extremely small thickness as compared to the cell monolayer and the stagnant liquid layer. On the other hand, cells affect oxygen transfer by two mechanisms: the biological enhancement due to the respiration of interfacial cells and the physical blocking resulting from the semipermeable nature of cell bodies. Due to the low specific oxygen uptake rates of the sludges, the two mechanisms were found to be of comparable importance in activated‐sludge systems; the oxygen transfer enhancement factor, E , varied from about 0.97 to 1.10 depending on the operating conditions. The biological enhancement effect, however, predominated in fermentations of actively growing bacteria. At relatively low agitation speed (e. g., 300 rpm), the value of E could reach about 3 to 5 in fermentations with high cell concentrations. Effects of other operating variables, such as the agitation intensity, the oxygen content in the mixed liquor, and the bulk cell concentration, on biological oxygen transfer enhancement were also studied. © 1992 John Wiley & Sons, Inc.