Harvesting Neochloris oleoabundans using commercial organic flocculants

Abstract

Microalgal cultures are inherently dilute, and increasing their concentration is essential for volume reduction and further processing. Flocculation is a classical operation in water treatment that is also used as a concentration step in microalgal biotechnology. However, flocculation is highly dependent on the physicochemical characteristics of the system, such as cell charge and concentration, pH, and solutes in the system, and the coagulant or flocculant to be used. This paper describes the efficiency of nine flocculating agents applied to Neochloris oleoabundans flocculation: low molecular weight chitosan; Zetag® 8165, 8185, 7652, and 4120; Magnafloc® LT22 and 351; and Tanfloc® SG and SH. The influence of flocculant concentration (from 3 to 16 mg L−1) and pH (from 6 to 10) was evaluated, showing a small influence of pH and a large influence of the type and concentration of flocculating agent. These effects are discussed regarding the flocculant charge and the zeta potential of the cells. The best flocculants were Zetag® 8185, Zetag® 8165, and chitosan, with floc sedimentation efficiencies higher than 95%. These flocculants were further evaluated for their efficiency in various concentrations at the native pH of N. oleoabundans cultures, with good efficiency. [Figure not available: see fulltext.].