PH influence on oxygen mass transfer coefficient in a bubble column. Individual characterization of kL and a

Abstract

Experiments were performed in a laboratory scale bubble column (10 L), to investigate the pH influenceon oxygen mass transfer coefficient, in order to achieve a better control of biological processes. Theliquid-side mass transfer coefficient, kL, and the specific interfacial area, a, were studied individually.The specific interfacial area was obtained using the new automatic image analysis technique developedby Ferreira et al. (2012). The pH was changed by the addition to the system of the most common acidsand base used in biological process: hydrochloric acid (HCl), phosphoric acid (H3PO4) and potassiumhydroxide (KOH). The results show that aqueous systems containing HCl, H3PO4 or KOH present lowervolumetric liquid side mass transfer coefficient, kLa, in relation to pure systems (distilled water), thisdecrease being not linear. It was found that the specific interfacial area presents higher values in KOHand HCl solutions in comparison with distilled water. However, an opposite behavior was observed inthe liquid-side mass transfer coefficient values. The kL behavior on the impure systems was explainedbased on bubble surface contamination. Higbie's and Froessling's equations were adapted in the špresent work in order to be used in bubble dispersion systems.