Study on the cell-collector-bubble interfacial interactions during microalgae harvesting using foam flotation

Area of Science:

• Biotechnology
• Chemical Engineering
• Environmental Science

Background:

• Foam flotation is a cost-effective method for microalgae harvesting.
• The precise interfacial interactions between microalgae cells, collectors, and bubbles are not fully understood.
• Existing hypotheses on microalgae foam flotation mechanisms require experimental validation.

Purpose of the Study:

• To elucidate the interfacial mechanism of microalgae-collector-bubble interactions during foam flotation.
• To quantify the adsorption of N-cetyl-N-N-N-trimethylammonium bromide (CTAB) on microalgae cells and bubbles.
• To determine the role of CTAB in modifying surface charges and facilitating microalgae capture.

Main Methods:

• Utilized cationic surfactant N-cetyl-N-N-N-trimethylammonium bromide (CTAB) as a collector.
• Quantified CTAB adsorption on Chlorella sorokiniana cells and air bubbles.
• Calculated zeta potential of cells and bubbles before and after CTAB adsorption.

Main Results:

• Over 90% of CTAB adsorbed onto bubbles, reversing their surface charge from negative (-20 mV) to positive (6.1 mV).
• Microalgae cells showed minimal CTAB adsorption (0-3%), with surface charge slightly shifting from -22.3 mV to -18.6 mV.
• A mechanism involving hydrophobic insertion of CTAB tails into bubbles and electrostatic attraction between positively charged bubbles and negatively charged cells was proposed.

Conclusions:

• CTAB primarily modifies bubble surface properties, not microalgae cell surfaces, for effective foam flotation.
• The study proposes a clear mechanism for microalgae-CTAB-bubble interactions, driven by electrostatic attraction.
• Understanding this mechanism can guide the development of improved collectors and devices for efficient microalgae harvesting.