Microalgal biofuel production

This study explores the use of seawater as a cost-effective and efficient substitute for freshwater in the cultivation of Chlorella sorokiniana SDEC-18 for biofuel production. Seawater enhances harvesting and lipid extraction, offering promising solutions to key challenges in large-scale algae-based biofuel production.

In a society with a growing need for sustainable energy resources, microalgae have emerged as a focal point in bioenergy research, holding the potential to replace fossil fuels in the future.

However, due to the current low efficiency of microalgal oil production and the high cost of investment in harvesting and extraction which accounts for more than 30% of biodiesel production costs, there is a need to find ways to make the process more sustainable and efficient. In response to this societal challenge, this research explores the viability of employing seawater as a substitute for freshwater in the cultivation of a microalgae, Chlorella sorokiniana SDEC-18, promising a better global future.

The benefits of seawater

Strikingly, compared to freshwater, seawater was found to:

  1. enhance Chlorella autoflocculation by reaching 90% settling efficiency within 2 hours,
  2. promote lipid accumulating by reaching about 60% (0.19–0.28 g/L of lipid concentration) due to salinity stress,
  3. improve lipid-extraction efficiency with full extraction achieved after only the second extraction step.

The mechanisms for enhanced Chlorella harvest were revealed through the observation of extracellular polymeric substances using transmission electron microscopy after lanthanum fixation. Moreover, new insights into cell fragility under salinity stress have been obtained through our pioneering proposal of the involvement of Chlorella microtubules.

The advances we have achieved in Chlorella harvesting and lipid extraction lay the foundation for a new generation of biofuel production, creating a more sustainable and efficient era within the bioengineering industry.

Comparison of extracellular polymeric substances, divalent metal ions and cell size from Chlorella sorokiniana SDEC-18 cultivated in BG11 medium, freshwater medium and seawater-based media
Observation of extracellular polymeric substances (EPSs) by location of La through transmission electron micrographs of Chlorella sorokiniana SDEC-18 on the final day. Orange ovals indicate magnified regions; Green arrows = EPS.

References

Pei, H, Zhang, L, Betenbaugh, MJ, Jiang, L, Lin, X, Ma, C, Yang, Z, Wang, X, Chen, S, Lin, W-F (2022) Highly efficient harvesting and lipid extraction of limnetic Chlorella sorokiniana SDEC-18 grown in seawater for microalgal biofuel production, Algal Research, 66, pp.102813-102813, ISSN: 2211-9264. DOI: 10.1016/j.algal.2022.102813.