Enhanced mixotrophic growth of microalga Chlorella sp. on pretreated swine manure for simultaneous biofuel feedstock production and nutrient removal

The objectives were to assess the feasibility of using fermented liquid swine manure (LSM) as nutrient supplement for cultivation of Chlorella sp. UMN271, a locally isolated facultative heterotrophic strain, and to evaluate the nutrient removal efficiencies by alga compared with those from the conventionally decomposed LSM–algae system. The results showed that addition of 0.1% (v/v) acetic, propionic and butyric acids, respectively, could promote algal growth, enhance nutrient removal efficiencies and improve total lipids productivities during a 7-day batch cultivation. Similar results were observed when the acidogenic fermentation was applied to the sterilized and raw digested LSM rich in volatile fatty acids (VFAs). High algal growth rate (0.90 d−1) and fatty acid content (10.93% of the dry weight) were observed for the raw VFA-enriched manure sample. Finally, the fatty acid profile analyses showed that Chlorella sp. grown on acidogenically digested manure could be used as a feedstock for high-quality biodiesel production.

► Chlorella sp. UMN271 is capable to utilize acetic, propionic and butyric acids. ► Acidogenic digestion of swine manure can improve the VFAs accumulation significantly. ► The acidogenic LSM can improve the algal growth, lipids content and nutrient removal.