Highly efficient harvesting and lipid extraction of limnetic Chlorella sorokiniana SDEC-18 grown in seawater for microalgal biofuel production

The low efficiency and high costs involved in harvesting microalgae and extracting lipids have been major barriers toward large scale algae-based biofuel production. Here we demonstrate the feasibility of employing seawater as a substitute for freshwater in cultivating Chlorella sorokiniana SDEC-18. Strikingly, compared to freshwater, seawater was found to 1) enhance Chlorella autoflocculation, reaching 90 % settling efficiency within 2 h; 2) promote lipid accumulation, reaching about 60 % (0.19–0.28 g/L of lipid concentration) due to salinity stress; and 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.