Synergistic interaction between metal ions in the sea salts and the extracellular polymeric substances for efficient microalgal harvesting

Artificial sea salts were found to cause microalgal flocculation and was so rather effectively in the presence of extracellular polymeric substances (EPS). EPS-producing species Ettlia sp. YC001 formed flocs at relatively low salt concentration: at 3.5 g/L, it reached up to 90% of the flocculation within 2 h. EPS non-producer Chlorella vulgaris UTEX 265, on the other hand, was less responsive to the salts even at 7 g/L and it had only 42% of floc formation. This phenomenon of salt-mediated flocculation appeared to be brought about mainly by calcium ion, as it has had greater affinity to the EPS than any other ions including the divalent magnesium ion. This sea salt-based coagulation may serve as one environmental-friendly alternative to commonly used chemical flocculants, which also potentially possess an economic merit.