Interactions of Chlorella vulgaris and fly ash cenospheres in heat-aided ballasted flotation

Abstract

Heat-aided ballasted flotation using industrial waste heat is a cost-effective and eco-friendly technology to harvest microalgae from aquatic environment. However, the underlying mechanism of this process is not yet fully understood. This study investigates the interactions between Chlorella vulgaris and fly ash cenospheres in heat-aided ballasted flotation based on the Extended Derjaguin-Landau-Verwey-Overbeek approach. The results indicated that Lifshitz-van der Waals interaction played an important role in the attachment of algal cell on fly ash cenospheres. Furthermore, the Lewis acid-base interaction changed from repulsion to attraction in the system due to heating, which promoted the algal cells to attach on fly ash cenospheres, resulting in a higher harvesting efficiency. However, when the temperature was increased to 90 °C, the Lifshitz-van der Waals interaction was reversed, which resulted in an energy barrier. The total attractive interaction increased with the decrease in pH from 10 to 4, due to changes in electrostatic interaction. After surface modification of fly ash cenospheres, the electrostatic interaction was always attractive in this system at pH of 7 regardless of temperature variations. Finally, according to the experimental results and the Extended Derjaguin-Landau-Verwey-Overbeek analysis, the usage of surface modified fly ash cenospheres for heat-aided ballasted flotation can be advantageous for environmental safety and high efficiency.