Using Oxygen Gas Transfer Coefficients to Predict Carbon Dioxide Removal

T. F. Aitchison, M.B. Timmons*, J.J. Bisogni Jr., R.H. Piedrahita, and B.J. Vinci

*Corresponding Author

Footnote
International Journal of Recirculating Aquaculture 8 (2007). All Rights Reserved
© Copyright 2006 by Virginia Tech and Virginia Sea Grant, Blacksburg, VA USA

ABSTRACT

The purpose of this research was to determine if oxygen gas transfer coefficients as reflected by overall mass transfer coefficient (KLa) values could be used to predict carbon dioxide (CO2) removal by degassing in aquaculture production systems.  The motivation for this approach was that while there is ample literature related to oxygen gas transfer, there is limited information on CO2 removal.  A series of tests was conducted to determine the ratio (fE) of KLa for CO2 to that for oxygen for two commonly used surface aerators and then compare fE to the theoretical ratio, fT, which is 0.90 based upon gas molecular diameters.  Experiments were conducted in a 10,000 L circular tank aerated by means of two different surface agitators.  The two aerators were selected to represent aeration patterns with high and moderate water to gas interface exposures or breakup patterns (photo supplied).  The results showed that fE/fT ratios were 96% (high air exposure) and 74% (moderate air exposure) for water with an alkalinity of ~130 mg/L as CaCO3.  The fE/fT ratio decreased to 0.84 and 0.51 for the high and moderate air exposures, respectively, when higher alkalinity waters (~1,000 mg/L as CaCO3) were used.