Microalgae as Sustainable Energy and Its Cultivation

Abstract

Growth of every country is depended on the ability to supply energy as per demand. Weather we notice it or not, the fact is energy is important in our daily life. The predicted expansion of world's population is at least 9 billion by 2050, correlates increase of energy use globally to 812 quadrillion (1015) kJ by 2035 from 533 quadrillion kJ in 2008. A key challenge is to meet the growing demand for energy in a safe and environmentally responsible manner. Sustainable energy serves the needs of the present without compromising the ability of future generations to meet their needs. Technologies that promote sustainable energy include renewable energy sources, and bioenergy is one of the types of renewable energy. Bioenergy is any organic material which can store sun light in the form of chemical energy. Algal biofuel has a potential to reduce the demand of fossil fuels for energy requirements. Algae production do not have a stringent requirement of environmental conditions and can be produced in aqueous suspensions where sufficient light and carbon dioxide is available. Biofuels from algae have a high lipid density (15-300 times higher than traditional crops) as compared with other terrestrial crops. Algae have a harvesting cycle of 1-10 days. The amount of biomass is doubled typically within 24 hours under optimal growth conditions (enough nutrients, sunlight etc.). The two major bioreactor classes of algae growth systems are open ponds and closed reactors. The most common growth systems used for commercial purposes are open pond. Open ponds are relatively inexpensive compared to closed photo bioreactor. Algae cells are sensitive to hydrodynamic stress. The concept of cell damage correlates interaction between free cells and isotropic turbulence eddies based on Kolmogorov's theory. When the micro-eddies size is close to the cell dimension, cell damage is higher; therefore, one should adjust the fluid flow in the open pond to maintain length of micro-eddies larger than the cell size. In the present investigation CFD code was used to study shear stress in open pond with side entry axial flow impeller. Three different channel lengths to width ratio were investigated with respect to size of micro eddies and shear stress.