Energy-Efficient Microalgae Filtering and Harvesting Using an Extremely Low-Pressure Membrane Filter with Fouling Control

Abstract

Microalgae (MA)-derived products have garnered increasing interest, resulting in expanded large-scale farming. The substantial energy required for MA harvesting constitutes a significant obstacle. This study assessed the energy-efficient harvesting of MA using Ultra-Lower-Stress Membranes (ULSM) filtering (<20 kPa) in conjunction with oxygenation. ULSM provided numerous advantages, particularly in minimizing energy usage, as it functioned at low Transmembrane Stress (TMS). Elevated TMS frequently correlates with increased pumping power, augmenting energy consumption. Membrane (MM) compression would significantly impact MMs with elevated TMS. The findings indicated that MM compression leads to a pure water permeability (PM) loss of up to 65% when the TMS is increased from 2.4 to 20 kPa. The permeabilities of Chlorella vulgaris broth diminished from 1650 and 1200 to 280 and 260 L/m²·hr·bar for the corresponding transmembrane pressures in systems with and without oxygenation. It was determined that MM fouled was more susceptible at low transmembrane pressure because inadequate foulant scoured from a low crossflow speed, resulting in PM reductions of up to 55%. MM fouling is the primary disadvantage of MM systems, as it diminishes MM efficiency. This research implemented aeration to prevent the fouling of MMs by dislodging foulants from the MM surface and holes. Reduced electrical consumption and improved filtering efficacy indicate that MM filtering integrated with an orifice presents a viable method for MA gathering, excelling in efficiency and accessibility. The particular electrical consumption for the ULSM was notably low, reaching up to 4.3 × 10^-3 kWh/m. A combination of low TMS and aeration results in minimal energy intake.