Proposal of a New Pathway for Microalgal Oil Production and its Comparison with Conventional Method

Abstract The use of fertilizers for microalgae growth is one of the major constraints for energetically feasible and sustainable production of fuel from microalgae at commercial scale. In a recent biological study, a distinct species of microalgae, Botryococcus braunii , which can produce long chain hydrocarbons and excrete them outside of the cell wall, has been tested for repetitive extraction of its hydrocarbons - termed as milking. The determination of the ability of the Botryococcus braunii to produce the hydrocarbons repeatedly without any extra supply of nutrients is expected to be an important step towards the sustainable production of fuels and chemicals from microalgae. In this study, the newly proposed method has been compared with the conventional method for the growth of microalgae to produce similar amount of microalgal oil. The mathematical models consisting of mass balance equations were developed using Aspen Custom Modeler for both the conventional microalgal growth system and the process of repetitive production of hydrocarbons from Botryococcus braunii . The results show that compared to the conventional system, the fertilizer requirement, water consumption and energy inputs in the milking process can be decreased by 90 %, 30 % and 70 %, respectively. This shows that the milking system has the potential to reduce the overall energy input to the process of production of fuel from microalgae. Also, high heating value of hydrocarbon contents of Botryococcus braunii gives the higher energy output resulting in higher output to input energy ratio of the process, making it energetically more feasible than the conventional system.