Hollow fiber nanofiltration: From lab-scale research to full-scale applications

This review provides a comprehensive overview on the quickly developing field of polymeric hollow fiber (HF) nanofiltration (NF), including membrane (module) and process design, operational parameters, and full-scale applications. Six different methods are currently used to produce HF NF membranes: phase inversion, interfacial polymerization, grafting, coating, polyelectrolyte multilayers (PEM) and chemistry in a spinneret. While all methods have their strengths and weaknesses, several PEM based membranes stand out because of their high chemical stability. This combination of geometry and chemical stability can make HF NF a sustainable alternative to spiral wound NF. This is especially the case for applications with a high fouling load where, in contrast to spiral wound NF, HF NF typically does not require an intensive pre-treatment. In academic settings, experiments are typically done in small modules with single-component feeds. Several studies showed that it is important, but not always straightforward, to correlate these lab scale results to full scale performance. Indeed, process design parameters such as crossflow velocity and staging partly determine energy consumption and retention and need to be taken into account. Partly based on these insights and developments, in the last five years commercial HF NF modules have rapidly become available. At least 59 pilot-scale and 26 full-scale HF NF plants are currently in operation or under construction, mostly focusing on water treatment. A comparison between these plants shows that HF NF can be applied for a broad range of applications with excellent scalability, highlighting the growth potential for HF NF in the coming years.