Harvesting of microalgae by flocculation with poly (γ-glutamic acid)

Area of Science:

• Biotechnology
• Marine Biology
• Chemical Engineering

Background:

• Microalgae are a promising source for sustainable biodiesel production.
• Efficient harvesting is a critical bottleneck in microalgal biomass utilization.
• Current harvesting methods can be costly and environmentally impactful.

Purpose of the Study:

• To evaluate poly (γ-glutamic acid) (γ-PGA) as an efficient and environmentally friendly microalgal harvesting agent.
• To optimize flocculation conditions for marine and freshwater microalgae species.
• To assess the impact of γ-PGA flocculation on microalgal cell integrity and lipid content.

Main Methods:

• Response surface methodology (RSM) was employed to optimize γ-PGA dosage, biomass concentration, and salinity for flocculation.
• Optimized protocols were applied to various microalgal strains including Chlorella vulgaris, Chlorella protothecoides, Nannochloropsis oculata, Phaeodactylum tricornutum, and Botryococcus braunii.
• Microscopic analysis was used to evaluate cell integrity post-harvesting.

Main Results:

• Optimized conditions yielded high flocculation efficiencies (≥90%) and concentration factors (>20) for tested microalgae.
• Specific optimal conditions were determined for marine Chlorella vulgaris and freshwater Chlorella protothecoides.
• Microscopic examination confirmed no significant damage to microalgal cell structures, indicating no lipid loss.

Conclusions:

• Poly (γ-glutamic acid) (γ-PGA) is a feasible and effective bio-flocculant for harvesting diverse microalgae species.
• This method presents a sustainable and cost-effective approach for microalgal biomass processing for biofuels.
• The preservation of cell integrity ensures the suitability of harvested microalgae for downstream lipid extraction and biodiesel production.