A 2-PLANE TUBULAR PHOTOBIOREACTOR FOR OUTDOOR CULTURE OF SPIRULINA

A photobioreactor in the form of a 245-m-long loop made of plexiglass tubes having an inner diameter of 2.6 cm was designed and constructed for outdoor culture of Spirulina. The loop was arranged in two planes, with 15 8-m-long tubes in each plane. In the upper plane, the tubes w ere placed in the vacant space between the ones of the lower plane. Th e culture recycle was performed either with two airlifts, one per plan e, or with two peristaltic pumps. The power required for water recycle in the tubular photobioreactor, with a Reynolds number of 4000, was 3 .93 X 10(-2) W m-2. The photobioreactor contained 145 L of culture and covered an overall area of 7.8 m2. The photobioreactor operation was computer controlled. Viscosity measurements performed on Spirulina cul tures having different biomass concentrations showed non-Newtonian beh avior displaying decreasing viscosity with an increasing shear rate. T he performance of the two-plane photobioreactor was tested under the c limatic conditions of central Italy (latitude 43.8-degrees-N, longitud e 11.3-degrees-E). A biomass concentration of 3.5 g L-1 was found to b e adequate for outdoor culture of Spirulina. With a biomass concentrat ion of 6.3 g L-1, the biomass output rate significantly decreased. The net biomass output rate reached a mean value of 27.8 g m-2 d-1 in Jul y; this corresponded to a net photosynthetic efficiency of 6.6% (based on visible irradiance). (C) 1993 John Wiley & Sons, Inc.