Assessment of flocculation induced by pH increase for harvesting microalgae Cyanothece sp.

One of the most important challenges lies in the microalgae mass production is the high cost of harvesting process which is the separation of a low amount of biomass consisting of small individual cells from a large volume of culture medium. Therefore, finding an efficient and costeffective technique for harvesting microalgae is important issue. In the current study, pH-induced flocculation method was tested for microalgae Cyanothece sp. harvesting. The halophilic microalgae were cultured and grown in laboratory with hypersaline water in F/2 medium. After reaching the stationary phase, the impact of pH induction (from natural medium culture pH:8.2 to pH:11) on flocculation efficiency, chlorophyll a, chlorophyll b, total carotenoid, β-Carotene and phycocyanin component and the possibility of reuse flocculated medium of microalgae Cyanothece sp. were evaluated. The results indicated that the increasing the medium pH value by adding NaOH from pH natural at 8.2 to 9.4 increased flocculation efficiency significantly from 10 up to 90% (P<0.05), but after that remained stable up to pH: 11. Regarding the pigment content, the increase in pH value from natural pH: 8.2 to pH: 9.1 had a relatively a medium effect on pigment components, including chlorophyll a, chlorophyll b, total carotenoid, β-Carotene and phycocyanin amount of the harvested biomass of Cyanothece sp, but after that from pH: 9.4 to 11 the reduction was severe. The medium culture from pH: 8.5 to pH: 11 was reusable for new culture of microalgae. Thus, the flocculation induced by pH increase up to pH: 9.1 is a suitable method for harvesting microalgae Cyanothece sp. with no serious adverse effect on pigment component.