Chitosan flocculation to aid the harvesting of the microalga Chlorella sorokiniana

► Chitosan is an effective flocculant to concentrate Chlorella sorokiniana cultures. ► With low dosage of chitosan clarification efficiency can reach >99% below pH 7. ► Flocculation reduces volume by 20–50 folds for subsequent cell harvesting process. Microalgae are an attractive feedstock for biofuel production, however the harvesting of algal biomass from very large volumes of culture broth represents a major technological and economic challenge. One low cost strategy for addressing this challenge involves the use of flocculation as an initial dewatering step. In this study, flocculation of the green microalga Chlorella sorokiniana was explored in detail using the natural compound, chitosan as flocculant. Results show that clarification efficiency of the process can reach above 99% below pH 7. The optimal chitosan dosage (approximately 10mg per gram algal dry weight) is determined primarily by cell concentration rather than cell age, lipid content or composition of the medium. Furthermore, the impact of flocculation on the subsequent dewatering process was determined and it was shown to reduce the volume to be processed by 20–50 folds, and significantly reduce energy input and material costs of centrifugation or filtration operations.