Carbon dioxide stripping in bubbled columns

Abstract

The carbonate buffer system plays a fundamental role in the biological treatments of wastewaters. In this work, the CO2 volumetric mass transfer coefficient (kLac) in a bubbled column was determined using the conventional titration method for different column volumes and air flow rates. In addition, a simple method to determine k Lac based on the interpretation of the changes in the pH level due to the CO2 stripping was developed. Results show that the apparent CO2 volumetric mass transfer coefficient (k Lac-app was strongly affected by the pH level; however, the actual CO2 volumetric mass transfer coefficient, k Lac = kLac-app/aα 0«, was constant within the tested pH conditions. In addition, kLac increased with higher air flow rates and lower column volumes; the obtained kLac values ranged between 20.0 and 71,9 h-1. For all the tested conditions, kLac values obtained using the noncontrolled pH method were similar to the values measured using the titrimetric method. The proposed mathematical model represented adequately the changes on the pH level and total inorganic carbon species concentration as a function of time. The model was extended to take into account the effect of phosphates. Simulation results showed that, although phosphates buffered the changes of pH, the losses of total inorganic carbon were faster than in the case of a nonbuffered solution; thus, the rise in the pH level prevented the stripping of CO2.