ABSTRACT
Recently Richmond and co-workers (1993) have reported a tubular bioreactor for outdoor culture of Spirulina in Israel. It consists of (a) an air-lift pump, (b) a gas separator and (c) transparent reactor tubing running in parallel and connected by manifolds (Figure 6.3). The reactor pipes are thin-walled extruded tubing of transparent polycarbonate (3.2 cm o.d., 3.0 cm i.d.). Such a design has the advantage
Figure 6.3 A tubular bioreactor installed at Microalgal Biotechnology Laboratory, Sede-Boker, Israel. (From Richmond et at., 1993, with permission.)
of reducing the amount of minor head losses compared with bioreactors arranged in the form of a loop in which the tubes are connected by U-bends, making it easier to scale-up in an industrial scale unit. Tubular photobioreactors are usually placed horizontally, but in recent years pilot vertical 'biocoil' facilities have been installed in the UK (Luton) and Australia (Borowitzka and Borowizka, 1989). The solar receptor is arranged as a coil of approximately 30 rnrn diameter low-density polyethylene tubing wound around an open circular framework (Figure 6.4). Temperature control is achieved by a heat exchange unit installed between the reactor and the pump. A 1300 1 unit would have an approximate photosynthetic surface area of 100 m2. With the biocoil it is possible to operate a ChlorelIa culture at a biomass concentration of up to 10 gl - ' without yield decline (Robinson, 1993). Finally, inclined tubular reactors have also been investigated for outdoor cultivation of microalgae (Lee and Low, 1991) and cyanobacteria (Hoshino et al., 1991) and are reviewed separately in this volume (Chapter 7).
