Simultaneous hexadecane and oxygen transfer rate on the production of an oil-degrading consortium in a three-phase airlift bioreactor

The hexadecane (HXD) transfer rate (HTR) and the oxygen transfer rate (OTR) were simultaneously evaluated as a single engineering criterion to enhance the production of an oil-degrading bacterial consortium. In order to accomplish the task, a 10-L three-phase airlift bioreactor (ALB) was used. Oxygen transfer volumetric coefficient (k(L)ao(2)) values of 25-49 h(-1) were found for several superficial gas velocities (Ug 0.15-2.7 cm s(-1)). HXD transfer volumetric coefficient (k(L)a(HXD)) values of 0.005-0.041 h(-1) were obtained for the same range of Ug values. OTR and HTR were calculated as the product of k(L)ao(2) or k(L)a(HXD) and the respective concentration gradient. HXD transfer parameters were evaluated by using an early reported novel technique. During 14 days culture, using constant Ug values, the ratio of HTR to OTR (HTR/OTR) never reached the stoichiometric ratio (0.25 +/- 0.05 g HXD (g O-2)(-1)). However, the productivity at the higher assayed constant Ug (2.7 cm s(-1)) was as good as 1.02 +/- 0.03 g SS (L d)(-1). We propose a variable Ug strategy that consumes 33% less energy than a higher constant Ug strategy to achieve the same yield and productivity. In this study, the oil-degrading consortium, able to remediate contaminated soils and water, productivity was successfully enhanced with simultaneous HXD and oxygen transfer considerations. (C) 2012 Elsevier B.V. All rights reserved.