Techno-economic evaluation of microalgae-based supply chain: Review on recent approaches

Third generation biomass-derived products such as biofuel has been garnering attention as a viable alternative energy source recently as it does not necessarily require fresh water and vast land for cultivation as compared to first-generation and second-generation biomass. However, extensive studies have to go into the feasibility evaluation for third generation biomass utilization prior to upscaling the process to commercial level. Other than comprehensive technical evaluation such as experimental studies to understand the microalgae productivity, economic evaluation of the utilization of third-generation biomass is also critical specifically in the perspective of supply chain. Therefore, the objective of this review is to lay out an overall picture to the readers the various option of approaches or methods utilized in feasibility evaluation of the microalgae-based supply chain. The outcome of the review paper indicated that approximately 58% of the papers reviewed opted for mathematical modeling with optimization whereas the remaining 42% opted for mathematical modeling without optimization.

Tolerance of Tetraselmis tetrathele to High Ammonium Nitrogen and Its Effect on Growth Rate, Carotenoid, and Fatty Acids Productivity

Microalgae can use either ammonium or nitrate for its growth and vitality. However, at a certain level of concentration, ammonium nitrogen exhibits toxicity which consequently can inhibit microalgae productivity. Therefore, this study is aimed to investigate the tolerance of Tetraselmis tetrathele to high ammonium nitrogen concentrations and its effects on growth rate, photosynthetic efficiency (Fv/Fm), pigment contents (chlorophyll a, lutein, neoxanthin, and β-carotene), and fatty acids production. Experiments were performed at different ammonium nitrogen concentrations (0.31–0.87 gL−1) for 6 days under a light source with an intensity of 300 μmol photons m−2 s−1 and nitrate-nitrogen source as the experimental control. The findings indicated no apparent enhancement of photosynthetic efficiency (Fv/Fm) at high levels of ammonium nitrogen (NH4+-N) for T. tetrathele within 24 h. However, after 24 h, the photosynthetic efficiency of T. tetrathele increased significantly (p < 0.05) in high concentration of NH4+-N. Chlorophyll a content in T. tetrathele grown in all of the different NH4+-N levels increased significantly compared to nitrate-nitrogen (NO3-N) treatment (p < 0.05); which supported that this microalgal could grow even in high level of NH4+-N concentrations. The findings also indicated that T. tetrathele is highly resistant to high ammonium nitrogen which suggests T. tetrathele to be used in the aquaculture industry for bioremediation purpose to remove ammonium nitrogen, thus reducing the production cost while improving the water quality.

Optimal integration of microalgae production with photovoltaic panels: environmental impacts and energy balance

Background Microalgae are 10 to 20 times more productive than the current agricultural biodiesel producing oleaginous crops. However, they require larger energy supplies, so that their environmental impacts remain uncertain, as illustrated by the contradictory results in the literature. Besides, solar radiation is often too high relative to the photosynthetic capacity of microalgae. This leads to photosaturation, photoinhibition, overheating and eventually induces mortality. Shadowing microalgae with solar panels would, therefore, be a promising solution for both increasing productivity during hotter periods and producing local electricity for the process. The main objective of this study is to measure, via LCA framework, the energy performance and environmental impact of microalgae biodiesel produced in a solar greenhouse, alternating optimal microalgae species and photovoltaic panel (PV) coverage. A mathematical model is simulated to investigate the microalgae productivity in raceways under meteorological conditions in Sophia Antipolis (south of France) at variable coverture percentages (0% to 90%) of CIGS solar panels on greenhouses constructed with low-emissivity (low-E) glass. Results A trade-off must be met between electricity and biomass production, as a larger photovoltaic coverture would limit microalgae production. From an energetic point of view, the optimal configuration lies between 10 and 20% of PV coverage. Nevertheless, from an environmental point of view, the best option is 50% PV coverage. However, the difference between impact assessments obtained for 20% and 50% PV is negligible, while the NER is 48% higher for 20% PV than for 50% PV coverage. Hence, a 20% coverture of photovoltaic panels is the best scenario from an energetic and environmental point of view. Conclusions In comparison with the cultivation of microalgae without PV, the use of photovoltaic panels triggers a synergetic effect, sourcing local electricity and reducing climate change impacts. Considering an economic approach, low photovoltaic panel coverage would probably be more attractive. However, even with a 10% area of photovoltaic panels, the environmental footprint would already significantly decrease. It is expected that significant improvements in microalgae productivity or more advanced production processes should rapidly enhance these performances.