IFTS - Institute of Filtration & Techniques of Separation Hall 8 / C47

Three new standards are available to qualify fluid process filter and are unique in the world. They have been developed under AFNOR committees to qualify filters for the power plant industries in a first time but can be used for pharmaceutical applications or water treatment industries.

NFX 45-303 has been updated in order to determine the particulate filtration efficiency and the retention capacity in such conditions the results are not biased by the clogging dust itself (such as cake filtration phenomena which may overestimate the filter performances).

NFX 45-310 has been updated to determine the burst differential pressure by following simultaneously the DP increase and the particle release.

NFX 45-308 has been updated to determine the behaviour of the filter cartridge to hot water circulation in terms of clogging conditions and on line downstream particle monitoring.

Both these 3 standards have been updated in order to give more confident results for the end users. This was an urgent request from the end user in order to prevent from bad interpretation of the test results Furthermore, they fix the test conditions in order to release a reference filtration rating , or a reference DP burst pressure in ambiant and hot conditions.

Much of the technical vocabulary used by filtration specialists is regularly used in other industries or even in everyday language, which creates biases or distortions in the interpretation of statements between parties trying to understand each other. This was clearly seen in March 2025 during Senate sessions in France, which attempted to shed light on the practices of bottled water producers: the lack of understanding of the precise terms used by filtration professionals, who consciously allow themselves to use codified shortcuts, does not facilitate communication with uninformed interlocutors. The message is further muddied when the commercial arguments of certain filter manufacturers or distributors highlight performance or characteristics that are unrelated to any methodological or normative reference or even simple explanation.

At IFTS, the Institute for Filtration and Separation Techniques, we felt it was important to make a useful contribution by providing technical insights into the topics discussed during these Senate examinations (membrane pore size and particle filtration efficiency), avoiding oversimplification while striving to remain understandable to as many people as possible.

This document presents the methods used to characterize microfiltration membranes, adopting a normative and scientific style. It details, in particular, the techniques used to measure pore size distribution, as well as performance (efficiency) tests based on particle retention.

This document indirectly highlights the need to fill certain gaps in European standards (EN standards) in the field of membrane filtration processes, particularly with regards to the vocabulary used and testing methods. Referencing these international European methods would be a valuable aid in avoiding any possible contradictory interpretations in the European regulations imposed in the field of water treatment.

There is a need to qualify ultrafiltration and nanofiltration membranes with a standardized methods.

Two specific protocols have been developped and proposed by AFNOR (french normalization committee) to determine the filtration ratings of membrane at size lower than 1 µm.

A first protocol (under NFX 45 103 reference) is based on macromolecules retention under a differential pressure and can be applied upon crossflow and dead end filtration membranes.

A second protocol (under NFX 45 -104 reference) is based on latex beads retention of size (0.1-1 µm) and is applied on dead-end filtration membranes in steady flow conditions.

The interest of such normative protocols is to express a reference filtration rating (in µm) to characterize in a reproducible way a filtration membrane. This is a need for end-users to help them choosing the different available membranes in the market.

Microplastic retention and accumulation in filtration membranes is increasingly recognized as a critical factor affecting membrane performance, fouling behavior, and long-term operational stability in water treatment processes. However, conventional characterization approaches provide limited insight into microplastic transport pathways within membrane structures and often rely on destructive or labor-intensive post-analysis.

This work presents an integrated experimental–modeling approach to investigate microplastic transport, retention, and clogging mechanisms in hollow fiber micro- and ultrafiltration membranes. Fluorescence-based detection using Nile Red staining is employed as a rapid, non-destructive diagnostic tool to directly visualize microplastic particles within aqueous systems and membrane structures, without extensive sample pre-treatment. The method enables spatially resolved detection of microplastics retained on membrane surfaces and within porous networks under controlled filtration conditions.

Fluorescence microscopy and emission spectroscopy are combined to monitor microplastic distribution and accumulation as a function of membrane pore size distribution, flow velocity, and particle characteristics. These experimental observations are coupled with pore network modeling to simulate microplastic transport, interception, and progressive pore blockage at the microscale. The model provides a mechanistic framework linking membrane structural properties to observed retention efficiencies and fouling patterns.

Results demonstrate that microplastic behavior in hollow fiber membranes is strongly governed by the interplay between pore size distribution and hydrodynamic conditions, leading to distinct retention and clogging regimes. The combined fluorescence–PNM approach allows direct comparison between membrane types and operating conditions, offering a powerful diagnostic tool for membrane selection and process optimization.

This methodology provides a practical pathway toward improved monitoring of microplastic fouling in filtration systems and supports the rational design of membranes with enhanced resistance to particulate contamination. The approach is readily adaptable to industrial membrane testing and offers potential for integration with real-time fluorescence monitoring strategies.