How Next-Generation High-Flux Seawater Desalination Membranes Achieve High Salt Rejection While Increasing Water Flux| Insights by AQUALITEK

Introduction

In seawater reverse osmosis (SWRO) systems, membrane performance has traditionally faced a fundamental trade-off:
higher water flux often leads to lower salt rejection.

However, the new generation of high-flux seawater desalination membranes has successfully broken this limitation. Through innovations in polymer chemistry, membrane morphology, surface engineering, and support-layer optimization, modern SWRO membranes now deliver:

•Higher water permeability

•Stable salt rejection (>99.8%)

•Lower operating pressure

•Reduced energy consumption

This article explores how material and structural design enable high desalination efficiency while increasing water flux.

1. Advanced Polyamide Chemistry for Selective Transport

1.1 Optimized Cross-Linking Density

Modern SWRO membranes rely on ultra-thin aromatic polyamide layers formed via interfacial polymerization.

Key improvements include:

•Precisely controlled cross-linking density

•Narrow pore size distribution at the molecular level

•Enhanced water transport pathways without enlarging salt passage channels

This allows:

•Rapid water diffusion

•Strong electrostatic and steric exclusion of salt ions

2. Ultra-Thin Active Layers with Structural Integrity

2.1 Thinner Is Better—But Only When Controlled

New-generation membranes feature:

•Active layers reduced to tens of nanometers

•Uniform thickness across the membrane surface

•Fewer defects and pinholes

Benefits:

•Shorter water transport distance

•Higher intrinsic permeability

•Maintained mechanical and chemical stability under high pressure

3. Nano-Engineered Surface Morphology

3.1 Optimized “Leaf-Like” or Ridge-Valley Structures

Advanced surface topologies:

•Increase effective membrane surface area

•Enhance local turbulence at the membrane interface

•Reduce concentration polarization

Results:

•Higher effective flux under the same operating pressure

•Sustained salt rejection even at high recovery rates

4. Hydrophilic Surface Modification

4.1 Enhanced Water Affinity

Surface engineering techniques include:

•Grafting hydrophilic functional groups

•Incorporating zwitterionic or polar moieties

•Plasma or coating-based surface activation

This improves:

•Water molecule attraction and transport

•Initial flux and long-term stability

•Resistance to fouling-induced flux decline

5. Charge-Based Ion Rejection Mechanisms

5.1 Electrostatic Exclusion (Donnan Effect)

New membrane materials are designed with:

•Stable surface charge distribution

•Negative charge dominance at operating pH

This enhances:

•Repulsion of chloride and sulfate ions

•Improved salt rejection without reducing permeability

•Better performance under variable salinity conditions

6. Low-Resistance Support Layer Design

6.1 Reduced Internal Concentration Polarization

The porous support layer is optimized through:

•Higher porosity

•Lower tortuosity

•Improved pore interconnectivity

Advantages:

•Reduced hydraulic resistance

•Enhanced water flow to the active layer

•Better performance at lower operating pressures

7. Mechanical Reinforcement for High-Pressure Operation

High-flux membranes must withstand:

•Operating pressures of 55–70 bar

•Pressure fluctuations and transient conditions

Structural enhancements include:

•Reinforced backing materials

•Optimized fiber orientation

•Improved bonding between active and support layers

This ensures:

•Flux stability

•Long membrane lifespan

•Consistent salt rejection over time

8. Fouling-Resistant Design for Long-Term Performance

8.1 Flux Is Meaningless Without Stability

High-flux membranes integrate:

•Smoother surface finish

•Lower surface roughness

•Anti-adhesion surface chemistry

Benefits:

•Reduced biofouling and organic fouling

•Slower flux decay

•Sustained desalination performance between cleanings

9. System-Level Compatibility and Energy Efficiency

High-flux membranes are designed to work with:

•Advanced energy recovery devices (ERDs)

•Lower feed pressures

•Optimized array configurations

System-level results:

•Reduced specific energy consumption (SEC)

•Lower operating cost per cubic meter

•Higher overall plant efficiency

Conclusion

The new generation of high-flux seawater desalination membranes achieves high desalination rates not by compromising selectivity, but by redefining membrane materials and internal structure at the molecular and nano scale.

Through:

•Advanced polyamide chemistry

•Ultra-thin, defect-free active layers

•Hydrophilic and charge-optimized surfaces

•Low-resistance support structures

modern SWRO membranes deliver higher water flux, stable salt rejection, and improved energy efficiency, making them a cornerstone of next-generation desalination plants.