**1.3. Cultivation of microalgae for biofuel production**

The development of dedicated culture systems for microalgae started in the 1950s when algae were investigated as an alternative protein source for the increasing world population. Subsequently, the diverse products and the bioremediation of wastewater potential of algae were explored. The initiation of research on algae as a source of renewable energy began by virtue of the energy crisis in the 1970s. The cultivation of algae requires few relatively simple conditions: light, water, carbon source, micro- and macronutrients and optimum temperature. Over the years, different culture systems have been developed keeping in mind the optimum conditions for microalgal growth, although it is a challenging task. The cultivation system for the growth of algae is an important requirement to aid in enhanced production of biofuels which includes open air ponds and closed controlled systems. The development of profitable algae-based fuel generation technology is yet in transition state wherein the final configuration is still to be explored and demonstrated at the industrial scale [29].

The cultivation of microalgae is a significant factor leading to enhanced biofuel production. The choice of cultivation system has to be emphasized because the phycoremediation efficiency and the yield of biofuels and other value-added products would largely depend on it. Broadly, the cultivation systems meant for microalgae are either open systems or closed systems. Hybrid systems, which are a combination of an open system and a closed system, can be used to achieve high biomass productivity with high nutrient removal [28].
