Production of Biodiesel from Marine and Freshwater Microalgae: A Review

Abstract

Aim: The increase in the annual global energy consumption over the past century has relayed heavily on fossil fuels. Fossil fuel burning have accelerated CO2 emissions on a global scale. CO2 makes up 63 % of the greenhouse gasses present in the atmosphere. The environmental concerns associated with greenhouse gas emissions emphasize the need for alternate energy sources that are more environmentally friendly. The aim of this paper was to review the availability of various types of algae for the production of biodiesel and other value added products and to investigate the factors that affect cell growth and lipid production in the cells, the various oil extraction methods, and the methods of conversion of the extracted lipids into biodiesel. Findings: Microalgae are abundant in nature and can be used as an alternate source of energy. They are photosynthetic microorganisms that are capable of growing in marine and fresh water environments and converting organic substances to oil. Their high growth rate, ability to produce large amounts of lipids which can be used for biodiesel production and to utilize CO2 present in the atmosphere for growth, makes them a good alternative to fossil fuel. Microalgae generate oil in the form of triacylglycerols which can be converted into biodiesel, via chemical or enzymatic a transesterification process. Biodiesel is a renewable fuel that generates the same amount of energy as that generated from petroleum diesel without the release of harsh compounds into the atmosphere, it is biodegradable and nontoxic and can be utilized in existing diesel engines without modification. Conclusion: Currently, the use of microalgae for biodiesel production is not economically feasible because of the high harvesting and pre-treatment costs associated with the production process. This can be overcome by extracting proteins, vitamins, carotenoids, nucleic acid, carbohydrates and lipids from the algae and processing the algae biomass into various value added products such as ethanol, methane, animal feed and fertilizer. Additionally, the glycerol produced as a by-product during lipid conversion into biodiesel can be further fermented to produce products such as methanol, lactic acid, ethanol and hydrogen. By producing these value-added products in addition to the biodiesel, the economics of the harvesting, pre-treatment and processing of microalgae into biodiesel can be improved significantly.