Enhancing the efficiency of thermal conversion of microalgae: a review

Nutrient stress as a tool for enhancement of yields and quality of biofuel products from thermal conversion processes has not received sufficient attention. Much research has been done on microalgal lipids conversion to biodiesel via the transesterification process route. However, the inefficient use of algae biomass due to the unutilized residual algal biomass and high production costs affect the economics and render the microalgal biodiesel technology less competitive to fossil-based fuels. Thermal conversion processes have gained increased attention since the processing can be applied to whole microalgae resulting in higher biofuel product yield and has the potential for producing other important products. The major challenges of thermal conversion processes of microalgae are the high level of nitrogen and oxygen content present in the product, which makes the bio-oil unstable for use as transportation fuels directly. Transportation fuels are expected to have low nitrogen content to meet environmental emission standards for combustion. Research efforts to address this challenge are ongoing, and the use of catalyst and co-thermal conversion of microalgae with other waste material has been proposed as possible options. Another promising yet to be explored approach with the thermal conversion process may involve the use of nitrogen nutrient alteration to manipulate the biomass composition to provide the requisite solution towards developing efficient and sustainable thermal conversion process for quality biofuel production from various species of microalgae.