Integrated Particle Size Classification and Baromembrane Filtration for Fouling Control in Natural Water Treatment

This article presents the results of theoretical and experimental studies on the mechanisms of natural water contamination via nanofiltration under turbulent flow conditions. A particle size classifier for natural waters has been developed that effectively describes the composition of the water; based on this, appropriate baromembrane filtration processes can be selected to ensure the gradual removal of particles of various sizes. The particle size classifier for natural waters serves as a tool for elucidating the mechanisms of nanofiltration fouling. Filtration of natural waters and model solutions was conducted under turbulent flow conditions (Re > 4000) using a laboratory cross-flow module and polyamide membranes with varying selectivity. It was found that the particle size distribution (PSD) of the deposit formed on the membrane surface systematically changes with membrane selectivity. A membrane with 80% selectivity retained larger particles (d₅₀ ≈ 5–15 μm). A membrane with 96% selectivity retained smaller colloids (d₅₀ ≈ 0.5–2 μm), increasing the fraction of 10–500 nm particles. Direct nanofiltration of highly turbid solutions (FTU 10–50) leads to rapid membrane fouling and a significant reduction in flux (>70%). Therefore, it is recommended to perform preliminary micro- and ultrafiltration of highly turbid solutions, reducing turbidity to FTU 2, followed by nanofiltration, which ensures the production of sterile water from heavily contaminated natural water. It was found that as membrane selectivity increases, the particle size distribution (PSD) shifts toward smaller colloids (10–500 nm), leading to the formation of a more compact precipitate. The results confirm that the particle size classifier in natural waters is an effective tool for studying contamination mechanisms and optimizing nanofiltration systems.