Carbon dioxide stripping in aquaculture – Part III: Model verification

Based on conventional mass transfer models developed for oxygen, the use of the non-linear ASCE method, 2-point method, and one parameter linear-regression method were evaluated for carbon dioxide stripping data. For values of KLaCO2KLaCO2 < approximately 1.5/h, the 2-point or ASCE method are a good fit to experimental data, but the fit breaks down at higher values of KLaCO2KLaCO2. How to correct KLaCO2KLaCO2 for gas phase enrichment remains to be determined. The one-parameter linear regression model was used to vary the CCO2* over the test, but it did not result in a better fit to the experimental data when compared to the ASCE or fixed CCO2* assumptions.For the packed column, the conventional mass transfer equation assumes that CCO2* is a constant within the column while the variable model assumes that CCO2* changes. When the column is divided into a large number of segments (300–500), the two models give comparable results because the change in mole fraction across an individual segment is small. For a smaller number of segments, the variable model is more accurate than the conventional model. K20CO2 values need to be computed from the variable mass transfer model because of the large change in mole fraction across the entire column. The variability of K20CO2 is reduced when the kinetics are slow (low pH and temperature). Future experimental work should start in this region and move toward faster kinetics (higher pH and temperature).

► For the non steady-state test, conventional methods are a good fit for KLaCO2KLaCO2 < 1.5/h. ► At higher values of KLaCO2KLaCO2, the fit breaks down for all the methods considered. ► The packed column can be modeled by the fixed or variable saturation models. ► K20CO2 values for the packed column must be computed from the variable saturation model. ► The variability of K20CO2 is reduced when the kinetics are slow (low pH and temperature).