Introduction
With increasing industrialization, urbanization, and stricter environmental regulations, the demand for high-quality water and advanced wastewater treatment technologies has grown significantly. Among emerging membrane technologies, nanofiltration (NF) membranes have become essential in advanced treatment and polishing processes. NF membranes, with a nominal pore size of approximately 1–2 nm, occupy the gap between ultrafiltration (UF) and reverse osmosis (RO) membranes. They are highly effective at selectively removing divalent and multivalent ions, as well as small organic molecules, while allowing partial passage of monovalent salts. This selective separation profile provides unique advantages in deep wastewater treatment, water reuse, and resource recovery.
1. High Removal Efficiency for Target Contaminants
NF membranes deliver excellent rejection of divalent and multivalent ions such as calcium, magnesium, and sulfate, which are primary contributors to water hardness and scaling. They also remove refractory organics, colorants, and trace pollutants that conventional biological or physicochemical processes cannot fully eliminate. In industrial wastewater treatment, NF membranes effectively reduce heavy metals, small molecular organics, and certain emerging contaminants, ensuring treated water complies with strict discharge or water reuse standards.
2. Moderate Operating Pressure and Energy Efficiency
Compared to RO membranes, which require high operating pressures, NF membranes operate at moderate pressures (typically 4–12 bar) while achieving effective removal of targeted ions and organics. This translates to lower energy consumption and reduced operational costs, making NF membranes an economical solution for large-scale industrial and municipal applications, particularly when complete desalination is unnecessary.
3. Operational Flexibility
NF membranes are compatible with diverse feed water sources, including municipal wastewater, industrial effluents, and landfill leachate. Their selective permeability allows retention of beneficial monovalent salts while removing problematic ions and organics. Applications include:
Water softening and scaling control in industrial processes
Removal of colorants, micropollutants, and trace organics for water reuse in manufacturing or agriculture
Pre-treatment for reverse osmosis, mitigating fouling and scaling and extending downstream RO membrane lifespan
4. Complementarity with Biological and Physicochemical Processes
In advanced wastewater treatment, NF membranes often complement secondary biological treatment and physicochemical methods. Biological processes efficiently degrade biodegradable organics, while NF targets refractory organics, divalent ions, and colorants. This synergy ensures higher effluent quality, lower chemical usage, and reduced environmental impact. NF membranes also provide a critical polishing step, producing water suitable for reuse or discharge compliance.
5. Resource Recovery and Circular Economy Applications
NF membranes facilitate resource recovery by selectively separating valuable salts and organic compounds. For instance, in textile, food, and pharmaceutical wastewater, NF can concentrate colorants, sugars, or salts for reuse, reducing raw material consumption and minimizing environmental discharge. In the context of a circular economy, NF technology enables transformation of wastewater into reusable water and recoverable resources, advancing sustainability goals.
6. Technological Advancements and Future Trends
Recent developments in membrane materials and surface modifications have enhanced NF performance. Thin-film composite (TFC) NF membranes exhibit excellent chemical resistance, thermal stability, and fouling mitigation. Additionally, computational modeling and predictive analytics are increasingly employed to optimize NF system design, forecast fouling and scaling, and reduce maintenance frequency. Emerging hybrid systems, combining NF with forward osmosis, advanced oxidation, or membrane distillation, are being explored for challenging wastewater streams such as landfill leachate or high-strength industrial effluents.
Conclusion
Nanofiltration membranes have established themselves as a key technology in advanced wastewater treatment. Their selective rejection of divalent/multivalent ions and small organics, moderate energy requirements, and operational versatility make them ideal for polishing and deep treatment applications. NF membranes complement biological and physicochemical processes, support resource recovery, and enhance the sustainability of water management systems. With ongoing innovations in materials and digital process optimization, NF membranes are poised to play an increasingly pivotal role in high-efficiency, sustainable water treatment worldwide.
