In general, conventional higher land plants are not very efficient in capturing solar energy. Even the fastest growing energy crops can convert solar energy to biomass at a yearly rate of no more than 1 W/m2 [133]. However, the biomass productivity of microalgae, a photosynthetic microorganism, can be 50 times greater than switch — grass [20]. Microalgae grow in marine and freshwater environments. Due to their simple cellular structure and submergence in an aqueous environment where they are in vicinity of water, CO2 , and other nutrients, microalgae are generally more efficient in converting solar energy into biomass. Microalgae can be used to pro­duce wide range of second-generation biofuels and bioactive compounds [47, 106]. They offer many potential advantages [14, 106, 133] over conventional biomass sources. Microalgae primarily comprise of varying proportion of proteins, carbohy­drates, lipids, and ash. The percentages vary depending upon the species. Table 5 presents the general composition of different microalgae. What really makes algal biomass feasible for biofuels production is the fact that many forms of algae have

very high lipid contents. The biomass that is nonlipid provides a high-value co­product such as animal feed or fertilizer that offsets the cost of converting the algae to fuels. Growing algae also removes nitrogen and phosphorus from water and con­sumes atmospheric CO2.