Development of a helical coagulation reactor for harvesting microalgae

Area of Science:

• Biotechnology
• Environmental Engineering
• Chemical Engineering

Background:

• Microalgae harvesting is crucial for biofuel and bioproduct applications.
• Conventional methods often face challenges with efficiency and cost.
• Polyaluminium chloride (PAC) is a common coagulant for microalgae flocculation.

Purpose of the Study:

• To develop and evaluate an innovative helical coagulation reactor (HCR) for microalgae harvesting.
• To investigate the impact of reactor design and hydrodynamic conditions on harvesting performance.
• To compare the HCR with a mechanically agitated vessel.

Main Methods:

• Development of a helical coagulation reactor (HCR).
• Investigation of construction and hydrodynamic characteristics (velocity gradient, Reynolds number).
• Comparative analysis with a mechanically agitated vessel at the same Camp number (Gt).

Main Results:

• Achieved a harvesting efficiency of 96.37% with large, compact flocs.
• Optimal settling rate of 20.51 m/h observed near the laminar-turbulent transition (Re=4000).
• Settling rate improved to 23.27 m/h under pulse flow conditions, forming larger, compact flocs.
• HCR demonstrated higher settling rates and shorter residence times compared to mechanical agitation.
• HCR operates with uniform energy dissipation and high velocity gradient, without electrical/mechanical energy input.

Conclusions:

• The HCR is an efficient and economic system for microalgae harvesting via sedimentation.
• Hydrodynamic conditions significantly influence floc properties and settling rates.
• The HCR offers advantages over traditional mechanical agitation in terms of efficiency and energy consumption.