Characteristics of Local Flow Dynamics and Macro-Mixing in Airlift Column Reactors for Reliable Design and Scale-Up

Abstract

There has been tremendous development within mixing operations in industry. Incomplete knowledge of this process caused serious economic losses to process industries. For optimum yields and the economic potential that goes with better understanding of mixing, research in this field continues to grow. The major forms of mixing in industry are either by mechanical or pneumatic agitation. Airlift bioreactors achieve mixing through pneumatic agitation and have gained attention over two decades for their fluid dynamic characteristics and low power consumption. It has been widely applied in bioprocess industries for production of biochemicals, to wastewater treatment in which the performance of this reactor has been overwhelming with respect to its production levels as compared to the conventional mechanical agitation.In this review, mixing through mechanical and pneumatic agitation is compared. An extensive literature is distilled from various investigators on the hydrodynamics and mixing characteristics of airlift bioreactors. This review has emphasis on factors that affect mixing such as the geometrical parameters of the vessel, gas flow rate, properties of the liquid medium, sparger design and measuring techniques employed. In an attempt to understand process related issues, sophisticated advances in the measuring techniques provides more insight into mixing in this reactor. Thus extensive correlations have been proposed by various investigators to predict the hydrodynamic and mixing parameters. Some design modifications proposed by several scholars have also been reviewed.