Multiphase Bioreactor Design

CHAPTER THIRTEEN

FLOCCULATION BIOREACTORS

ANTÓNIO A.VICENTE, MANUEL MOTA AND JOSÉ A.TEIXEIRA

Department of Biological Engineering, Universidade do Minho, 4710–

057 Braga, Portugal

ABSTRACT

One of the main goals of bioprocess engineering is to increase the

productivity of biotechnological processes and a vigorous progress has

been observed in that field over the last decades. Fermentation based

processes are not an exception and, in order to achieve those objectives,

techniques such as the use of high cell density systems have been

proposed and studied. The interest for such systems is increasing for they

seem to be a very promising alternative to the traditional cell suspension

fermentation. In fact, they may increase volumetric productivity, product

concentrations in the outlet and conversion of raw materials, as a higher

biomass concentration (biocatalyst) is present, at any moment, inside the

bioreactor. Downstream processing will also be improved by the use of

these technologies, as smaller amounts of biomass will be present in the

effluent of the bioreactor.

To achieve this, several new processes were studied, changes in

existing ones were introduced and technical developments were made.

The examples are various and cover diverse applications such as ethanol,

beer and antibiotics production, and waste water treatment, just to quote a

few representative areas. Among the several immobilisation techniques,

flocculation, although not being extensively considered, is one of the most

attractive.

In this chapter, the main aspects associated with high cell density

cultures using flocculating microorganisms will be considered. Aspects

such as bioreactor design and performance, mass transfer limitations in

cell aggregates and their relation with yeast cell activity, as well as

applications, will be considered and discussed.

Keywords: floes, three-phase bioreactor, airlift, mass transfer,

hydrodynamics, design

INTRODUCTION

Systems using flocculating cultures (Abate et al., 1996; Kida et al., 1992; Kuriyama et
al., 1993; Roca et al., 1995; Teixeira et al., 1990; Wieczorek and Michalski, 1994) which
take advantage of cell recycling by natural sedimentation of highly flocculating strains