Physical structure determines compression of membrane biofilms during Gravity Driven Membrane (GDM) ultrafiltration

Area of Science:

• Membrane science and engineering
• Environmental microbiology
• Biophysics

Background:

• Transmembrane pressure (TMP) increases hydraulic resistance in membrane biofilms through compression.
• Understanding biofilm compression mechanisms is crucial for optimizing filtration processes.

Purpose of the Study:

• To investigate how membrane biofilm compression occurs and how structural rearrangement affects hydraulic resistance.
• To evaluate the impact of different nutrient conditions on biofilm structure and response to pressure changes.

Main Methods:

• Biofilms were grown in membrane fouling simulators (MFS) under varying nutrient conditions (enriched, P-limited, river water).
• Structural and hydraulic responses to cyclic changes in TMP and permeate flux were monitored.
• Optical coherence tomography (OCT) quantified biofilm thickness and roughness (Ra).

Main Results:

• Heterogeneous biofilms (Ra > 0.2) from enriched and river water conditions exhibited irreversible compression, decreased roughness, and increased hydraulic resistance.
• Homogeneous biofilms (Ra < 0.2) from P-limited conditions showed reversible compression and full recovery of hydraulic resistance.
• Hydraulic response did not consistently correlate with structural changes in heterogeneous biofilms.

Conclusions:

• Biofilm physical structure significantly influences its response to transmembrane pressure changes.
• Irreversible compression and increased hydraulic resistance in heterogeneous biofilms have practical implications for GDM filtration systems.
• Reversible compression in homogeneous biofilms suggests potential for operational resilience.