ABSTRACT
The industrial production of microalgae is profitable for specific applications, either very high-value molecules such as nutraceuticals (e.g., omega 3, 522carotenoids) or whole microalgae produced using a low-cost process such as fish larva feed for aquaculture or Spirulina as a dietary supplement. However, producing biofuel or building block molecules for the chemical industry with microalgae is not economically viable at the moment.
For this kind of nonmature technology, techno-economic analyzes (TEA) can be of great help regarding two main ambitions: (i) many process options are to be explored especially for microalgae biofuel production and TEA is a practical tool for comparing them on similar bases. The process pathways with the best potential can then be specified, and (ii) sensitivity analyzes of TEA can identify key parameters and processes on which research efforts need to be addressed in order to decrease the production cost or improve the energetic and environmental balances.
The first TEAs on microalgae biofuel production have pointed out the drying as the most energy intensive step in the process. Since then, wet conversion processes such as hydrothermal liquefaction or wet lipid extraction have been preferred. Microalgae cultivation is the step with the highest impact on the economics of the whole biofuel production process. Reducing its cost is a major and crucial challenge. Sensitivity analyzes have shown that microalgae productivity is the most important factor for economically and energetically viable microalgae biofuel production. This validates the actual research efforts on screening and selecting highly efficient microalgae strain.
In the context of a difficult economic viability, the use of waste streams (i.e., wastewaters for nutrients and flue gases for CO2) and the recycling of process waters are strongly recommended. The biorefinery concept needs to be applied to the microalgae biofuel production process.
Similarly, the valorization of the entire biomass is needed. Co-products such as pigments or omega 3 can be of great help to make the process profitable, especially now, at an early stage of the microalgae biofuel industry. However, when the full-scale of microalgae biofuel production will be reached, the market sizes of biofuel and these high-value molecules will not be compatible. At that time, animal feed, human food and bioremediation will emerge as serious covalorization opportunities.
