A Simple Reliable Bioreactor for Studying the Growth and Metabolism of Photosynthetic Micro-organisms in Space

A membrane photobioreactor was designed, implemented and used to grow the cyanobacterium Arthrospira platensis PCC 8005 in batch mode. Growth was followed directly by monitoring optical density and indirectly by measuring pressure increase due to the oxygen produced and separated from the liquid phase by diffusion through a hydrophobic membrane. When the pressure attained an upper limit, valves opened automatically and the oxygen in the gas chamber was flushed out with nitrogen. The reactor was operated for over 700 h. As expected, two growth phases were observed, a short exponential phase followed by a linear phase indicating limitation by light transfer. The growth rate during the second phase was measured easily and accurately, yielding data relevant to CELSS design.