Enhanced microalgae separation using metastable froth in flotation

• Applicant: Dr.-Ing. Sascha Heitkam, since 9/2023
• Subject Area: Mechanical Process Engineering
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 502434290

Algae have drawn much attention in the past decades not only because of their successful application for clean energy production and wastewater treatment, but also because they have shown an enormous potential for food, cosmetics and pharmaceutical industry. However, despite the various potentials, a major challenge regarding algae application is the efficient and cost effective separation from cultivation media. Various methods such as filtration, centrifugation, gravity sedimentation and flotation have been utilized until now. All of these methods have their own drawbacks. However, flotation appears promising due to its lower cost and the capability for extending to large scales. In algae flotation, collectors are added to the solution, rendering the algae surface hydrophobic. Then, small air bubbles are introduced to the suspension, picking up the hydrophobized algae and transporting them to the top of the container. There, a froth is formed where the liquid drains down and high algae concentration is achieved. Despite of many works published on algae flotation, the algae behavior in the froth has not been studied systematically yet. This is while the froth stability is an important factor in flotation since it regulates the drainage process in the froth zone. The project aims for efficient microalgae recovery in flotation while avoiding harmful substances consistent with food and pharmaceutical applications. We firstly focus on achieving a proper algae adsorption to the rising bubbles by investigating the interfacial properties of the formed collector-algae complexes in detail in order to adjust the composition of the algal suspension. Afterwards, we design the froth zone in a way to have a metastable froth in order to enhance the algae grade in the extract. A metastable froth is stable enough to flow over the weir. However, it is encountered with rapid coalescence, which increases the bubble size in the column. The larger bubbles at the top accelerate the liquid drainage leading to a dry froth and a high grade. For precise formulation of a metastable algae froth, we study the influence of algae on film instability using a single film. Thereby, the dynamics of the film thinning and the statistics of the film rupture are investigated in presence of algae in a well-controlled system. Afterwards, we explore the stability of the froth through dynamic foam analysis where the liquid drainage and bubbles coalescence are measured with time. The results of film and froth analysis will provide a model of the froth stability in dependency of algae concentration, surfactant concentration, liquid fraction and froth age. The model will be incorporated in a model of the froth flotation process in order to tune the flotation cell parameters regarding the optimum drainage and coalescence to achieve the highest recovery and grade in the flotation experiments.

• DFG Programme: Research Grants
• International Connection: France
• Cooperation Partner: Professorin Wiebke Drenckhan, Ph.D.
• Ehemaliger Antragsteller: Dr. Behnam Keshavarzi, until 8/2023