The Optimization of Chlorella vulgaris Flocculation Harvesting by Chitosan and Calcium Hydroxide

The high cost for microalgae harvesting still is the bottleneck of microalgae commercial production. In the present study, the effect of adjusting pH to alkaline conditions with sodium hydroxide/calcium hydroxide and the addition of chitosan together with pH adjustments on the flocculation of Chlorella vulgaris (C. vulgaris) was studied, respectively. A single-factor experiment showed a maximum flocculation efficiency of 96.7% when adjusting the pH to 12 with calcium hydroxide. There was synergistic action between chitosan and calcium hydroxide. Flocculation conditions of C. vulgaris for the combined use of calcium hydroxide and chitosan was optimized by response surface methodology (RSM) with a Box-Behnken design (BBD). Flocculation efficiency reached 97.08% under optimal flocculation conditions when adjustion of pH to 8.97 with 2 g/L calcium hydroxide, a chitosan dosage of 20 mg/L, and a flocculation time of 60 min. The current study presents one method for efficient flocculation harvesting of C. vulgaris at weak alkaline conditions and low chitosan dosage.