Microwave assisted flocculation for harvesting of Chlorella vulgaris

Microalgae harvesting is a major hindrance for the development of the microalgae industry. In this paper, short microwave treatment was used to assist the flocculation of Chlorella vulgaris with three flocculants, Fe³⁺ (FeCl₃), chitosan, and Ca²⁺ (CaCl₂). A microwave irradiation time of 20 s, and a pH of 10 was found to be the optimum condition. The harvesting efficiency could be significantly increased by 43.2%, 49.5% and 39.6%, respectively for Fe³⁺, chitosan, and Ca²⁺ assisted by microwave under these conditions. Microwave treatment did not cause any damage to the algal cells, and had no obvious influence on the lipid extraction. Microwave treatment decreased the concentration of the flocculants in culture medium after flocculation; this treatment enabled the reuse of the supernatant. This study provides a new and promising method of improving the flocculation efficiency for microalgae harvesting, by using microwave energy.