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Role of Transmembrane Pressure and Water Flux in Reverse Osmosis Composite Membrane Compaction and Performance
Jishan Wu1,2, Jinlong He3,4, Javier A Quezada-Renteria1
1Department of Civil & Environmental Engineering, University of California, Los Angeles, California 90095, United States.
Environmental Science & Technology
|April 23, 2025
Summary
High transmembrane pressure (TMP) significantly compacts thin-film composite reverse osmosis (TFC RO) membranes, impacting performance. Flux-induced forces also drive compaction, with support layer compaction being irreversible.
Area of Science:
- Materials Science
- Chemical Engineering
- Environmental Science
Background:
- Thin-film composite (TFC) reverse osmosis (RO) membranes are crucial for water desalination.
- Membrane compaction under operating pressure affects long-term performance and efficiency.
- Understanding compaction mechanisms is vital for optimizing membrane design and operation.
Purpose of the Study:
- To investigate the compaction behavior of TFC RO membranes under varying transmembrane pressure (TMP) and water flux.
- To elucidate the roles of TMP and flux in membrane structural changes.
- To differentiate between reversible and irreversible compaction mechanisms.
Main Methods:
- Crossflow filtration system operated at controlled feed pressure and osmotic pressure.
- Varied TMP and water flux by adjusting feed solution osmotic pressure.
- Characterized membrane compaction using scanning electron microscopy (SEM) and molecular dynamics (MD) simulations.
- Evaluated membrane performance through wet-testing.
Main Results:
- Membrane compaction increased with rising TMP and water flux, reaching up to 30% at 50 bar TMP.
- SEM and MD simulations showed compaction in both the polyamide active layer and polysulfone support layer.
- Higher TMP led to reduced water permeability but increased water flux, salt rejection, and salt permeability.
- Compaction was largely irreversible in the support layer but reversible in the active layer.
- Flux-induced frictional forces were identified as a significant factor in compaction dynamics.
Conclusions:
- Transmembrane pressure is a primary driver of TFC RO membrane compaction, affecting both active and support layers.
- Flux-induced drag forces contribute significantly to structural deformation and compaction.
- Irreversible compaction of the support layer and reversible compaction of the active layer dictate overall membrane response to pressure cycling.
- These findings provide insights for improving RO membrane durability and performance.
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