Harvesting marine microalgae species by chitosan flocculation

Marine microalgae are still an important larval feeding source. One of the most promising harvesting techniques of the algae produced appears to be chemical flocculation. We report results obtained with chitosan flocculation of five marine species of microalgae of importance to mariculture (Skeletonema costatum, Dunaliella tertiolecta, Thalassiosira nordenskoldii, Chlorella sp. and Thalassionema sp.). The algae were grown in the laboratory in 20-liter batch cultures under normal conditions in artificial seawater. Without pH control, a 100% flocculation efficiency was reached at fairly high chitosan concentrations (above 40 mg liter^?1). When the final pH was adjusted to around 7·8–8·0, a 100% flocculation efficiency was obtained with chitosan concentrations of 40 mg liter^?1 or more. However, when pH was adjusted to around 7 or less, prior to chitosan addition for S. costatum and Chlorella sp., the concentration of chitosan required to obtain a 95–100% flocculation efficiency was reduced to 20 mg liter^?1 for Chlorella and 2 mg liter^?1 for S. costatum. The results are discussed in the light of the currently accepted theories on flocculation.