Algal Physiology and Large-Scale Outdoor Cultures of Microalgae

Abstract

The reliable and efficient production of microalgae in large-scale commercial culture, whether in open ponds or in closed photobioreactors, requires a good understanding of the physiology of the alga being cultured. Since large-scale cultivation is almost always carried out outdoors, the algae experience an environment which changes during the day, from day-to-day, and also seasonally. Key environmental factors are light and temperature, and efficient use of the available light is critical for obtaining maximum productivity. How algal cell metabolism is regulated under such conditions is important as is the ability of the algae to acclimate to changed environmental conditions. Algal productivity and the formation of desired cell products such as carotenoids (e.g. $β$-carotene and astaxanthin) or long-chain polyunsaturated fatty acids is further affected by nutrient sources and availability and the nutrient requirements of the algae under intensive large-scale culture need to be understood. The availability of inorganic carbon either as carbon dioxide or bicarbonate is especially important. Understanding of the physiology and biochemistry of the algae also enables manipulation of the culture conditions to optimise the productivity of the desired algal metabolite (product). Understanding diurnal and circadian rhythms may also aid in optimising culture conditions and maximising yields by adjusting the timing of harvesting. Monitoring of large-scale cultures is difficult and also requires a good understanding of the physiology of the algae.