Atrazine adsorption from aqueous solution using powdered activated carbon - Improved mass transfer by air bubbling agitation

A set of batch adsorption kinetic tests of atrazine adsorption by powdered activated carbon (PAC) was performed using air bubbling as the mixing method. It was found that air bubbling at appropriate rates could achieve good mixing. Even a slight turbulence generated by a few bubbles could provide a reasonable mixing to facilitate PAC adsorption compared with unstirred processes. The estimated mass transfer coefficient in the liquid film surrounding the PAC particles increased linearly with the increase in air bubbling rate up to a plateau value. The experimental mass transfer coefficients in the bubbling system compared favorably with values calculated using correlations developed for conventional magnetic stirring systems, with the help of a conversion of the bubbling rates to the equivalent stirring speeds. The effect of intermittent air bubbling on the adsorption rate was also tested by generating bubbles intermittently at different net air flow rates. It was found that at the same net flow rate, intermittent higher intensity sparging could be more efficient for the PAC adsorption than continuous lower intensity sparging. This suggests that intermittent high intensity bubbling is the preferable operation, with the potential not only to assure good PAC adsorption efficiency but also to reduce the air/energy consumption. (c) 2005 Elsevier B.V. All rights reserved.