Efficient microalgae harvesting mediated by polysaccharides interaction with residual calcium and phosphate in the growth medium

Abstract

This study sets out to harvest microalgae through auto-flocculation by manipulating the interactive effect of calcium, phosphate, and polysaccharides (PSAs). The harvesting efficiency (H.E) of 91 +/- 2.7% was achieved for Ettlia sp. through auto-flocculation. The H.E was attributed to the chelation of calcium and PSAs present in microalgae medium. In the absence of PSAs, the H.E reduced to 64 + 05% only. The addition of phosphate (34 +/- 0.13 mg L-1) increased the H.E to 73 +/- 1.5%. Zeta-potential measurements showed that the harvesting was induced by charge neutralization and inter-particle bridging. The PSAs-based auto-flocculation was tested for Chlorella sp. too but it turned out the H.E of 51 +/- 1.3% only. The flocculation did not take place when the co-harvesting of Ettlia sp. and Chlorella sp. was carried out. It is concluded that each microalgae specie shows different auto-flocculation mechanism due to variation in their PSAs characteristics. It triggers up the need for setting up a distinct protocol for different microalgae species to assess their auto-flocculation potential. (C) 2019 Elsevier Ltd. All rights reserved.