The nanofiltration is a pressure-driven membrane process that is located between ultrafiltration and reverse osmosis. It is used to remove dissolved substances such as salts, organic molecules and hardness formers from water. With a typical pore size of 0.001 to 0.01 micrometers, nanofiltration offers selective separation and enables the removal of multivalent ions and large organic molecules, while some of the monovalent ions (e.g. sodium and chloride) remain in the permeate.
Table of contents
Technical basics
Nanofiltration membranes often consist of thin polymer layers, such as polyamide compounds, which are applied to carrier materials. The membranes are arranged in spiral elements, which enable a compact design and a high specific membrane surface area.
Operation
Nanofiltration works under a pressure range of 4 to 30 bar, depending on the application and the desired separation capacity. The filtration process generates two streams:
- Permeate: Purified water with reduced salt and hardness content.
- Concentrate: Water with increased concentration of retained substances.
Functionality and mechanisms
Nanofiltration separates dissolved substances by diffusion and sieving. It is able to do this:
- Polyvalent ions (e.g. calcium, magnesium) and
- Organic molecules (e.g. pesticides, humic acids)
are effectively retained. One-part ions such as sodium and chloride partially pass through the membrane, resulting in a lower retention rate compared to reverse osmosis.
Photo: ALMA Mem UF nanofiltration module in stainless steel design, installed in the ALMA Modul technical room container
Areas of application
Water softening
- Removal of calcium and magnesium ions to reduce water hardness in industrial processes.
Drinking water treatment
- To remove heavy metals, pesticides and organic compounds while reducing the salt content.
Food and beverage industry
- Concentration of milk proteins and desalination of whey.
Pharmaceutical industry
- For the treatment of process water where selective ion removal is required.
Wastewater recycling
- For recovering water from industrial wastewater, for example in the textile or paper industry.
Advantages of nanofiltration
- Selective ion removal: Retention of monovalent ions and selective retention of polyvalent ions.
- Lower operating pressure compared to reverse osmosis, which saves energy.
- Wide range of applications: Flexible use for different water qualities and requirements.
- Protection of downstream systems: Reduces scaling and fouling in downstream processes such as reverse osmosis.
Photo: Individual ALMA MEM UF nanofiltration systems for industrial water treatment
Challenges and maintenance
Typical problems with nanofiltration are fouling and scaling, which are caused by deposits of organic substances or salts. The following measures are recommended to minimize these effects:
- Regular dry cleaning (CIP).
- Use of antiscalants to prevent scaling processes.
- Pre-treatment of the water, e.g. by filtration or chemical conditioning.
ALMAWATECH solutions
ALMAWATECH offers customized nanofiltration systems that are specially adapted to the requirements of industrial processes. Our systems are characterized by high efficiency, modular design and state-of-the-art control technology. Our pilot tests allow us to determine the ideal membrane configuration and operating mode for your specific water treatment project.
Conclusion
Nanofiltration is a highly specialized technology that bridges the gap between ultrafiltration and reverse osmosis. It offers an energy-efficient and selective solution for removing hardness constituents, organic compounds and polyvalent ions. This versatility makes it a key technology in modern water treatment and industrial water management.
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