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Biomass feedstocks refer to a wide range of biological, renewable materials that can be used or converted into fuels, such as ethanol, biodiesel, oil, etc. Food crops are examples of first generation feedstocks, such as corn and wheat. The second-generation feedstock include rice straw, switch grass and other forms of non-food materials. Algae is considered the third generation biofuel raw material (Wang 2013). Algae can grow in different water environments, such as freshwater, sewage and saline. They contain higher lipid and protein content than other terrestrial plants. Two types of algae include macroalgae and microalgae. .
Macroalgae are multi-cellular organisms that often grow in ponds. Microalgae are single-celled and smaller types with strong photosynthesis capacity. They essentially use sun light, water and carbon dioxide from the air to make sugar and oxygen through photosynthesis for growth (Wen 2009). They grow quickly and can double in biomass size in 3.5 hours at the peak phase. Microalgae has high oil content between 20-50 % (dry weight) that can generate biofuel. Other crops may take the entire season to grow and contain lower level of oil, approximately 5% dry weight of oil (Chisti 2007). More than 20,000 types of microalgae are identified in the ocean and freshwater (Wang 2013). Microalgae can grow in various types of waters, such as sea saltwater, alkaline and also waste water, making it advantageous to produce energy in areas with freshwater shortage. The short cell cycle and fast reproduction, simple structures, and high oil content provide additional advantages to utilize microalgae as feedstocks to produce large-scale bioenergy. .
Microalgae cultivation and production are the first step in the energy generation pathway, in order to produce and harvest good quality and amount of microalgae materials, before they can be converted into necessary biofuels. Different conversion processes will generate respective biofuels, such as fermentation producing bioethanol, and pyrolysis producing bio-oil and biogas (Office of Energy Efficiency and Renewable Energy).
