Chapter 4Airlift Bioreactor

Schematic Diagram

Evolved from bubble column concept Recirculation of liquid through a downcomer

connecting the top and bottom of the main bubbling section

Efficient mixing by high circulation flow rate No mechanical agitators – no large shear

forces Can satisfy a high oxygen demand Eg. production of secondary metabolites by

plant cells

Introduction

Two types: ALR with internal loop and ALR with external loop

Continuous injection of air at the bottom of the riser creates a density difference with the downcomer as the air escapes at the top of the reactor.

Because of the density difference, a liquid flow from the bottom to the top exists in the riser and from the top to the bottom in the downcomer, resulting in circulation of continuous liq phase.

The Construction

The absence of mechanically moving parts A low shear rate A low defect rate Adequate gas-phase disengagement at the

top Unique combination of controlled flow and

good mixing properties Well-defined residence time Easily operated under sterile conditions

Advantages of ALR

Internal loop ALR (AILR) External loop ALR (AELR)

Types of ALR

A well-defined residence time in the individual sections of AELR

An adjustable gas-phase disengagement at the top

Accessability for measurement and control in both riser and downcomer

Excellent heat exchange and temp control Optimal hydraulic diameter for both riser

and downcomer and therefore low friction rate

Advantages of AELR compared to AILR