Using nano-chitosan for harvesting microalga Nannochloropsis sp.

► Nano-chitosan performed better than chitosan in terms of biomass recovery and dosage. ► Biomass recovery was increased by 9% for nano-chitosan. ► Optimum dosage by adjusting pH was decreased by 40% for nano-chitosan. ► The best initial cell density was 665 × 106 cells/ml for minimum flocculant dosage consumption. ► Recycled water of flocculated medium with carbon content increases algae growth.