Lipid‐based liquid biofuels from autotrophic microalgae: energetic and environmental performance

Abstract

Commercial cultivation of autotrophic microalgae for food production dates back to the 1950s. Autotrophic microalgae have also been proposed as a source for lipid-based liquid biofuels. As yet, there is no commercial production of such biofuels and estimated near-term prices are far in excess of fossil fuel prices and prices of biofuels based on terrestrial food oil crops. Future costs of autotrophic microalgal lipid-based biofuels are very uncertain. The energetic return of energy investment in liquid autotrophic microalgal biofuels is below a factor 5, even if optimistic assumptions are made about future technologies. Available studies do not allow for firm estimates of life cycle greenhouse gas emissions of autotrophic microalgal lipid-based biofuels. Apart from greenhouse gases, life cycle pollutant emissions of autotrophic microalgal biodiesel may well be more of an environmental burden than the life cycle pollutant emissions linked to fossil diesel or biofuels based on canola or switchgrass. Whether the prospects for, and performance of, lipid-based biofuels from autotrophic microalgae in the more distant future will much improve appears to be largely dependent on breakthroughs in

Elevated CO2 improves lipid accumulation by increasing carbon metabolism in Chlorella sorokiniana

“…An alternative approach would be to supply microalga with extra CO 2 for scale-up lipid production as has been done previously (Reijnders, 2013;Shen, 2014). However, the molecular and cellular mechanisms underlying lipid accumulation under high doses of CO 2 have not been fully elucidated.…”

“…These results could suggest that carbon may also be 'pushed' into FA via carbohydrate metabolism by high doses of CO 2 . When excess carbon is supplied, rapid growth of the cells may consume more nitrogen, which results in a significant increase in C/N (Reijnders, 2013;Shen, 2014). This case may mimic the N deprivation state and therefore LS-2 may exhibit a similar response mechanism.…”

“…An alternative strategy would be to provide excess carbon in the form of carbon dioxide (CO 2 ), whereby growth and lipid accumulation might be achieved in a so-called one-stage process (Cheng et al, 2013). Extra CO 2 supply is believed to be a more promising approach for scale-up lipid production than nitrogen deprivation because microalgae may assimilate CO 2 from the flue gas of factories, thereby upgrading this waste stream into usable products such as lipid (Reijnders, 2013;Shen, 2014). Microalgae are so far the only species known to be able to utilize extremely high levels of CO 2 up to 20% (Solovchenko and Khozin-Goldberg, 2013).…”

Regulatory mechanisms of lipid biosynthesis in microalgae

“…Transcriptome analysis of the marine green alga Nannochloropsis oceanica IMET1 pointed to the progressive redirection in the flux of carbon precursors from protein and carbohydrate synthesis to glycerolipid synthesis during nitrogen starvation (Li et al, 2014). Indeed, the supply of excess carbon (either as CO 2 or in organic form) induced rapid cell growth with concomitant elevated nitrogen consumption, resulting in an increased C/N ratio (Reijnders, 2013). After Chlorella sorokiniana cultures supplied with high doses of exogenous CO 2 were exposed to nitrogen starvation, enzymes in the Calvin cycle, glycolysis (which converts the intermediate G-3-P from the Calvin cycle into pyruvate), and putative transporters that direct pyruvate to the plastid (e.g.…”

Review of life cycle greenhouse gases, air pollutant emissions and costs of road medium and heavy‐duty trucks

“…LCA are internationally standardized tools used to assess impacts in production processes and are also suitable for assessing the sustainability of goods and processes ('D'Amato et al, 2020). LCAs are also often considered the proper way to compare the energy and environmental performance of specific fuels or energy supply (Reijnders, 2013).…”