MICROALGAE HARVESTING THROUGH PH MEDIATION AND OYSTER-DERIVED CHITOSAN: EFIICIENCY, FATTY ACID PROFILE AND ECONOMIC CONSIDERATION

Abstract

Microalgae are known as sustainable feedstock for biofuel production but efficient and economical harvesting method remain a major challenge for large scale production of algae. This study investigates harvesting efficiency of marine microalgae Gonyostomum sp. using two sustainable flocculation techniques- including Bio-flocculation via chitosan extracted from oyster shells and pH induced flocculation. The effect of different chitosan dosages (100 - 500 mg/L) and varying pH levels (8 - 11) on the harvesting efficiency and fatty acid methyl ester (FAME) profile was assessed. The results demonstrated 90 ± 0.3% efficiency with 500 mg/L single flocculant chitosan and a maximum efficiency of 97 ± 0.1% at pH 11. Lipid content of harvested biomass exhibited that pH mediated and chitosan mediated flocculation exhibited lower lipid yield (15.20 ± 0.9% and 17.80 ± 1.2%) compared to the centrifugation (21.86 ± 0.8%). Fatty acid methyl ester (FAME) profiling showed that there was significant difference (p < 0.05) among the quality of lipids of different harvesting methods. An indicative chemical cost analysis demonstrated that pH-induced flocculation is substantially more economical (2.24 BDT/L or 0.0184 US$/L) than chitosan-based harvesting (57.84 BDT/L or 0.4743 US$/L). These findings imply that both strategies are viable for achieving high flocculation efficiency. Although the usage of chitosan incurs a higher cost than pH mediation, its use encourages waste valorization and environmental sustainability, whereas pH mediation provides a scalable and inexpensive substitute.