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Transfer of Carbon Dioxide within Cultures of Microalgae: Plain Bubbling versus Hollow‐Fiber Modules
Author(s) -
Carvalho Ana P.,
Malcata F. Xavier
Publication year - 2001
Publication title -
biotechnology progress
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.572
H-Index - 129
eISSN - 1520-6033
pISSN - 8756-7938
DOI - 10.1021/bp000157v
Subject(s) - mass transfer , fiber , carbon dioxide , membrane , biomass (ecology) , microporous material , chemical engineering , raw material , hollow fiber membrane , photosynthesis , mass transfer coefficient , materials science , chemistry , chromatography , composite material , organic chemistry , ecology , biochemistry , engineering , biology
In attempts to improve the metabolic efficiency in closed photosynthetic reactors, availability of light and CO 2 are often considered as limiting factors, as they are difficult to control in a culture. The carbon source is usually provided via bubbling of CO 2 ‐enriched air into the culture medium; however, this procedure is not particularly effective in terms of mass transfer. Besides, it leads to considerable waste of that gas to the open atmosphere, which adds to operation costs. Increase in the interfacial area of contact available for gas exchange via use of membranes might be a useful alternative; microporous membranes, in hollow‐fiber form, were tested accordingly. Two hollow‐fiber modules, different in both hydrophilicity and outer surface area, were tested and duly compared, in terms of mass transfer, versus traditional plain bubbling. Overall volumetric coefficients ( K L a ) for CO 2 transfer were 1.48 × 10 − 2 min − 1 for the hydrophobic membrane, 1.33 × 10 − 2 min − 1 for the hydrophilic membrane, and 7.0 × 10 − 3 min − 1 for plain bubbling. A model microalga, viz. Nannochloropsis sp., was cultivated using the two aforementioned membrane systems and plain bubbling. The produced data showed slight (but hardly significant) increases in biomass productivity when the hollow‐fiber devices were used. However, hollow‐fiber modules allow recirculation of unused CO 2 , thus reducing feedstock costs. Furthermore, such indirect way of supplying CO 2 offers the additional possibility for use of lower gas pressures, as no need to counterbalance hydrostatic heads exists.