Comparison between the removal of live and dead algae using froth flotation

Froth flotation separation was used to remove Scenedesmus quadricauda, an algae species which is commonly found in lakes and reservoirs, from an aqueous suspension as a function of several variables. The removal efficiencies of both live and dead algae (thermally terminated) using the froth flotation method as a function of the introduction of two types of surfactant, aeration rates, pH and temperature of operation are compared. The characteristics of the algal suspension such as the zeta potential of the algae and the surface tension measurements are also reported. Cetyltrimethylammonium bromide (CTAB), a cationic surfactant species, gave a comparatively good algal removal efficiency while sodium dodecylsulphate (SDS), an anionic surfactant species, gave, in comparison, a relatively poor removal efficiency. By decreasing the ambient pH values of the algal suspensions, the SDS gave an increasingly better extent of separation. As the aeration rates were increased, the removal efficiencies of both the live and the dead algae were increased slightly whereas when the temperature increased from 20 to 40°C, the removal rates were, more or less, unchanged. In most cases, the removal of the dead algae was greater than that of the live algae. The surface tension of the dead algal suspensions with CTAB was slightly lower than that of the live algal suspensions with CTAB at comparable concentrations, which may facilitate the removal of the dead algae.