Use of chitosan acid solutions to improve separation efficiency for harvesting of the microalga Chlorella vulgaris

The significance of chitosan as a flocculant for microalgae harvesting is well recognized. However, the effects of solvent in dictating the solubility of chitosan, which in turn, influence the separation efficiency (SE) of microalgae, are not explored yet. In this study, at first, self-flocculation efficiency of Chlorella garis was determined in different growth stages. The highest self-flocculation efficiency was found in stationary phase (22 +/- 2%) and the lowest in exponential phase (0.25 +/- 0.02%). Subsequently, the SE of C vulgaris (in stationary phase) was measured by using four different chitosan-dissolved acids (0.1 M) as flocculants. Citric acid containing chitosan showed the lowest SE of 5.1 +/- 5% followed by nitric acid (54.5 +/- 5.65%), phosphoric acid (69.3 +/- 2.47%), and hydrochloric 84.5 +/- 3.53%, respectively. The effects of flocculant dose and mixing rate on the SE were identified. The cells showed the maximum SE at 30 mg/L of chitosan and 300 rpm mixing rate. Zeta-potential measurement confirmed that the flocculation was induced by charge neutralization. (C) 2013 Elsevier B.V. All rights reserved.