Impacts of cationic polyacrylamide flocculant and elevated pH on the harvesting of the diatom Phaeodactylum tricornutum

Abstract

Microalgae are considered a promising source of biocompounds due to their rapid growth and high lipid content. The present study aimed to evaluate the efficiency of biomass separation of the diatom Phaeodactylum tricornutum through flocculation and high pH induction. It also examined how this separation method affected the fatty acid profile and fatty acid methyl esters (FAMEs) content of the biomass. Cultures of P. tricornutum were harvested in both the stationary and exponential phases and treated with different biomass dilution values (0, ½, and ¼) for each phase. Biomass separation was achieved using three concentrations (5.0, 7.5, and 10.0 mg L−1) of cationic polyacrylamide (CPA) flocculant and one treatment with high pH induced by sodium hydroxide. The sedimentation time after treatment application was 15 min. Fatty acid and FAMEs analyses were conducted on the biomass in the stationary phase. The use of NaOH resulted in efficiency values ranging from 94.82 to 99.40%, while CPA achieved efficiency values between 98.55 and 99.95%. Total fatty acid analysis showed a predominance of monounsaturated fatty acids with CPA and saturated fatty acids with NaOH. The FAMEs yield of biomass separated with NaOH was 21.7% lower than the highest yield obtained with CPA. It is recommended to use 5 mg L−1 of CPA in the stationary phase without diluting the biomass for optimal separation of PTR biomass. Due to the negative impact of NaOH on fatty acid composition and FAMEs yield, its use is not recommended.