Using Ferric Sulfate, Sodium Hydroxide, and Chitosan to Harvest Marine Microalgae Chlorella Vulgaris and Recycling the Culture Medium

Abstract

Microalgae are widely used in biofuels, medicine, food, and feed industries. However, harvesting microalgal biomass is a major difficulty that hinders their industrial application. In this study, three flocculants (ferric sulfate, sodium hydroxide, and chitosan) were used to harvest the marine microalga Chlorella vulgaris, and floc characteristics including flocculation efficiency, concentration factor, and flocs morphology were studied. The results showed that the tested flocculants can efficiently harvest C. vulgaris. The flocculation efficiencies of ferric sulfate (0.9 g/L), sodium hydroxide (0.6 g/L), and chitosan (30 mg/L) were 93.4% ± 0.8%, 96.5% ± 0.6%, and 98.8% ± 1.3% within 70, 100, and 12 min, respectively. The total carbohydrates, proteins, and lipids contents in C. vulgaris were not influenced by the test flocculants after harvesting. When compared with fresh f/2 medium, the recycled medium could also efficiently support C. vulgaris growth. Among the three flocculants tested, chitosan was ideal owing to its high efficiency, low dosage requirement, short harvesting time, and reutilization of culture medium.