Application of an airlift reactor with a net draft tube in phenol bio-oxidation using Ralstonia eutropha

Abstract

Phenol biodegradation by Ralstonia eutropha was studied in a constructed airlift reactor with a stainless steel net draft tube (ALR-NDT). In giving a description of the cell performance, it is necessary to quantify the relationships between the bioreactor characteristics (gas holdup (ε_G), time of mixing (t_m), and gas–liquid mass transfer coefficient (K_La)) and the cell bioprocesses. Thus, the hydrodynamic properties of the reactor were measured using air–water and air–mineral salt solution (MSS) systems. The K_La value for the MSS system in ALR-NDT was 1.2 times higher than the bubble column reactor and airlift reactor as modified versions of the ALR-NDT. Improvement in t_m was also considerable for air–MSS in the ALR-NDT. At higher superficial gas velocities (U_Gs), ALR-NDT performance was better in terms of ε_G obtained for air–MSS compared with an air–water system. Growth and phenol consumption by R. eutropha followed substrate inhibition kinetics, and the experimental data for the specific growth rates at three different U_Gs were fitted to the Haldane, Edwards and Aiba–Edwards models. Between these models, the latter gave the best fit according to the goodness of fit results. The estimated kinetic parameters were indicative of a high potential for R. eutropha in degrading phenol.

Keywords:

• Airlift reactor with net draft tube
• Gas holdup
• Gas–liquid mass transfer coefficient
• Growth kinetics
• Ralstonia eutropha

Acknowledgments

The authors express their thanks to Dr Samaneh Sanjari for her valuable assistance.