A technique for harvesting unicellular algae using colloidal gas aphrons

Abstract

Unicellular algae have proven to be extremely difficult to separate from their liquid environment, and at the present time no economical process exists. A novel technique using colloidal gas aphrons (CGA) has been investigated for harvesting <i>Chlorella vulgaris</i>, a green algae, from dilute suspension. CGA dispersions consist of very small gas bubbles, on the order of 25 microns in diameter, that are each encapsulated in an aqueous shell of surfactant solution. The process is based on the technology of CGA flotation, which involves the formation of algae-bubble complexes (possibly including dissolved inorganic ions) and their subsequent flotation into a stable froth at the surface. At neutral pH, the efficiency of algae removal was maximized when a cationic surfactant (lauryl pyridinium chloride) was used for CGA generation. At pH 10, both the cationic and anionic (sodium dodecyl benzene sulfonate> CGA dispersions yielded comparable removals. Addition of small quantities of alum (to 10^-4 M) improved removals using the cationic CGA, and at pH 10 this combination yielded the maximum removals that were achieved: 52.1% removal after a single application of CGA dispersion (1 to 1, dispersion to sample volume ratio), and 89.2% removal after an additional application. Although the of CGA-flotation has yet to be determined, it is proposed that the process occurs through the interaction of the CGA bubbles, the algal cells, and possibly dissolved ions to form buoyant flocs.