1. Introduction

The primitive earth consisted of an atmosphere filled with CO₂ which could not sustain any life forms. The advent of life on earth was possible due to Cyanobacterium and algae. They sequestered the atmospheric CO₂ via photosynthesis and in turn released molecular oxygen. This led to a rapid decrease in CO₂ levels as a result of which life started evolving on earth. Time has come once again that these humble organisms save us from the threat of global warming. The conversion of solar energy to chemical energy is the major attribute of all photosynthetic organisms including algae. The energy gets stored in the cells as oils, carbohydrates and proteins. The conversion of solar energy to chemical energy largely depends on the photosynthetic efficiency of the organism. Algae are the most photosynthetically efficient organisms on earth which makes them a prospective feedstock for different purposes. The oil production by microalgae is much higher as compared to any other oil crop. Algal biotechnology could provide a plausible solution to many problems ranging from green house gas emission reduction to treatment of wastewater and generation of value added products. Algae are diverse in nature and can be found from unicellular to complex and differentiated levels. They generally inhabit damp surroundings and are abundant in terrestrial as well as freshwater and marine environments. Similar to all photosynthetic organisms, algae require sunlight, carbon dioxide and water for their growth. The affinity of CO₂ for microalgae is very high which makes them a prospect for CO₂ mitigation. The productivity of oil per acre is the highest in microalgae and it can surpass any other oil crop for biodiesel production. Moreover, it does not require arable land for growth and can be sustained on wastewater (Demirbas A, Energy Educ Sci Technol A 23:1–13, 2009a).