Combining patterned membrane filtration and flocculation for economical microalgae harvesting.

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Membrane technology shows promise for microalgae harvesting but is hindered by membrane fouling and high costs due to low fluxes.
• Patterned membranes can mitigate fouling through enhanced turbulence and increased active surface area.
• Flocculation aids microalgae harvesting by increasing particle size and reducing free organic matter.

Purpose of the Study:

• To investigate the impact of polyethylene glycol (PEG) concentration in patterned polysulfone membranes on microalgae harvesting performance.
• To evaluate the effects of cross-flow velocity and chitosan dosage on membrane fouling and permeance.
• To estimate energy consumption and harvesting costs for full-scale microalgae harvesting.

Main Methods:

• Fabrication of patterned polysulfone membranes with varying polyethylene glycol (PEG) concentrations in the casting solution.
• Filtration experiments using microalgae suspensions to assess membrane permeance and fouling under different cross-flow velocities.
• Integration of flocculation using chitosan to evaluate its effect on membrane performance and filtration resistance.
• Estimation of energy consumption and harvesting costs based on experimental results.

Main Results:

• The patterned membrane with 28w% PEG exhibited the highest clean water permeance (900±22 L/m²·h·bar) and microalgae suspension permeance (590±17 L/m²·h·bar).
• Patterned membranes demonstrated significantly lower filtration resistance (15% permeance decline) compared to flat membranes (72%) at 0.0025 m/s cross-flow velocity.
• Optimal conditions combining patterned membrane filtration with flocculation at a specific chitosan dosage yielded the highest stable membrane permeance (110±17 L/m²·h·bar) and lowest filtration resistance.
• The optimized process achieved very low energy consumption (0.28 kWh/kg) and harvesting costs (0.16 €/kg).

Conclusions:

• Polyethylene glycol concentration is crucial for tuning the performance of patterned membranes in microalgae harvesting.
• Patterned membranes combined with flocculation offer a superior solution for reducing fouling and increasing permeance.
• The developed method presents a cost-effective and energy-efficient approach for large-scale microalgae harvesting.