Extracellular polymeric substances trigger microalgae flocculation in a combined and green flocculation-flotation...

Area of Science:

• Biotechnology and Bioengineering
• Renewable Energy and Biomass Production
• Separation Science and Process Engineering

Background:

• Microalgae are a promising sustainable feedstock, but their industrial use is limited by inefficient and costly harvesting methods.
• Current harvesting technologies often struggle with scalability and economic viability, posing a significant bottleneck for microalgal biomass utilization.

Purpose of the Study:

• To develop and optimize a cost-effective, combined flocculation-flotation harvesting technique for microalgae.
• To investigate the synergistic effects of a bio-flocculant (cationic guar gum) and a fatty acid-based collector (sodium hydroxysulfonate stearate, OA-1) on microalgae harvesting efficiency.

Main Methods:

• A combined flocculation-flotation process was designed using cationic guar gum and OA-1.
• Plackett–Burman experimental design was employed to identify key process parameters: flocculant dosage, collector dosage, and aeration rate.
• Extracellular polymeric substance analysis, proteomic profiling, and Extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory were used to elucidate the underlying mechanisms.

Main Results:

• Optimized parameters yielded a high harvesting efficiency of 91.2% and a biomass enrichment factor of 27.8.
• The synergistic process significantly increased median floc size (by 209.2%), improved compactness, and reduced floc moisture content (by 9.6%) compared to single flocculation.
• EDLVO theory successfully explained the interaction between OA-1 and microalgal flocs, demonstrating a 73.1% reduction in the energy barrier, promoting aggregation.

Conclusions:

• The integrated flocculation-flotation approach offers a highly efficient and potentially cost-effective method for microalgae harvesting.
• The study highlights the critical role of extracellular polymeric substances and provides mechanistic insights into the synergistic flocculant-collector interactions.
• This optimized harvesting strategy advances the industrial viability of microalgae as a sustainable biomass feedstock.