Adrian MichaelsWhat Is Nano-Filtration?
Nano-filtration is a modern membrane filtration technique primarily applied to water with low total dissolved solids, like surface and fresh groundwater, aiming to soften it by removing multivalent ions and to eliminate by-products such as natural and synthetic organic materials.
Applications Of Nano-Filtration In Industry
Increasingly, nano-filtration finds its use in the food industry, for the dual purposes of concentration and selective demineralisation of monovalent ions. This process utilises membranes with nanoscale pores, typically ranging from 1 to 10 nanometers, falling between micro-filtration and ultrafiltration in terms of pore size, and slightly larger than reverse osmosis pores. These membranes are usually crafted from polymer thin films, with common materials including polyethylene terephthalate and various metals. The precise control of pore size is achieved by manipulating the pH, temperature, and development time, allowing for pore densities between 1 and 1 million pores per square centimetre.
Traditionally, the primary application of nanofiltration in water treatment has been for softening purposes. This is achieved by its ability to selectively filter out divalent ions, while permitting smaller monovalent ions to pass. This contrasts with ion exchange processes, which typically add sodium ions to the water. Nanofiltration, therefore, offers the advantage of softening water without the introduction of additional elements.
Nano-Filtration Advantages
Nanofiltration’s advantages over centrifugation include its higher precision in filtration, particularly in selective removal of solutes. This makes it suitable for applications requiring detailed separation at the molecular level. Nanofiltration’s membrane-based process allows it to treat a wider range of substances compared to centrifugation, which is limited to separation based on density and size. In agro-industrial applications, nanofiltration efficiently handles waste streams, a task where centrifugation might not be as effective. Moreover, nano-filtration systems can be optimised for energy efficiency and tailored to specific industry requirements, offering operational flexibility.
Reverse osmosis, known for its finer filtration capabilities, can remove almost all particles and contaminants, resulting in nearly pure water. However, it also strips out essential minerals like calcium, magnesium, and potassium, which have known health benefits. Some reverse osmosis systems address this by incorporating a remineralization step.
While reverse osmosis offers a higher level of purification, nano-filtration operates at slightly lower pressures, leading to potential energy savings. Nano-filtration is particularly effective at removing harmful organic substances, including pesticides, without completely stripping the water of beneficial minerals. This selective filtration is advantageous for maintaining the taste and nutritional value of drinking water.
Despite its benefits, nanofiltration is not as commonly employed in industrial membrane filtration, reserved for specific scenarios where pore size specifications fall into its narrow operational range.
