Biological Principles of Mass Cultivation of Photoautotrophic Microalgae

The principles involved in mass cultivation of microalgae outdoors are elucidated. Solar photosynthetic active radiation (PAR) represents the major limiting growth factor in correctly maintained cultures (where temperature and nutrients are essentially not growth limiting), of photoautotrophic microorganisms This is well reflected in their cultivation protocol, which sets to reduce limitations on cell growth and thereby facilitate most efficient use of PAR. Several approaches are used in an attempt to address the major challenge of establishing the optimal light regime for the average cell in the culture to reap maximal productivity under given environmental constraints. The basic parameters involved in mass cultivation are elucidated. These include cell density and its ramifications, the rate and method of culture mixing, the pivotal role of the optic path, light-dark (LD) cycle frequency, growth inhibition, photosynthetic rates, and efficiency with reference to effective use of strong light, maintenance of monoalgal cultures outdoors, and considerations of reactor design as well as the reactors' spatial setting, based on direct exposure to the solar beam or avoidance of such exposure.