A low-cost and scalable process for harvesting microalgae using commercial-grade flocculant

Area of Science:

• Biotechnology
• Environmental Science
• Chemical Engineering

Background:

• Microalgal biomass production is crucial for biofuels and bioproducts.
• Efficient and low-cost harvesting remains a significant bottleneck in microalgal cultivation.
• Current methods often involve expensive chemicals or energy-intensive processes.

Purpose of the Study:

• To develop a low-cost, scalable, and efficient harvesting process for Chlorella sp. FC2 IITG.
• To improve the overall process economy of microalgal biomass feedstock production.
• To evaluate the feasibility of recycling nutrient-rich spent water and optimizing flocculant dosage.

Main Methods:

• Screening of commercial grade flocculants (ferrous sulphate and ferric chloride).
• Evaluation of harvesting efficiencies at varying flocculant doses.
• Assessment of recycled spent water for successive microalgal growth over six batches.
• Scale-up studies in a 5 L photobioreactor and a 350 L open raceway pond.

Main Results:

• High harvesting efficiencies (>99.8%) achieved with low doses of ferrous sulphate and ferric chloride.
• Ferrous sulphate demonstrated superior performance in spent water recyclability for multiple batches.
• Recycled spent water supported comparable growth kinetics and nutrient recovery to control samples.
• Harvesting cost estimated at $0.17-0.3 USD/kg biomass using commercial ferrous sulphate.

Conclusions:

• A cost-effective and scalable microalgal harvesting process was successfully demonstrated.
• Utilization of commercial flocculants and recycled spent water significantly reduces production costs.
• The optimized process eliminates the need for pH adjustment and separate inoculum development.