Microalgae harvesting using colloidal gas aphrons generated from single and mixed surfactants

Harmful algal blooms (HABs) caused by microalgae are becoming increasingly common and pose serious threats to human health, aquaculture, and marine environments and, therefore, their removal is becoming essential. Colloidal gas aphrons (CGAs), a recent technology adapted in flotation, showed promise in removing several contaminants from aqueous solutions. This study aimed to investigate the potency of CGAs in removing several microalgae strains (Spirulina platensis, Nannochloropsis oculata, and Chlorella vulgaris) from aqueous solutions. Surfactants, including cationic hexadecyl trimethyl ammonium bromide (HTAB), anionic sodium dodecylbenzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), and their mixes, were used to prepare stable CGAs. The effect of different environmental parameters like algae concentration, pH, and salinity, on removing Spirulina platensis was thoroughly investigated. Operating conditions, including surfactant type, flotation time, flowrate, and solution temperature, were optimized. At pH 5 and 50 °C, Spirulina platensis, Chlorella vulgaris, and mixed microalgae were fully removed using CGAs produced from cationic HTAB surfactant. About 95% removal of Nannochloropsis oculata was achieved using mixed surfactant CGAs. The results obtained from this work demonstrated the promising potential of CGAs produced from both single and mixed surfactants in harvesting various microalgae from aqueous media.