Tourmaline triggered biofilm transformation: Boosting ultrafiltration efficiency and fouling resistance

Ultralow pressure filtration system, which integrates the dual functionalities of biofilm degradation and membrane filtration, has gained significant attention in water treatment due to its superior contaminant removal efficiency. However, it is a challenge to mitigate membrane biofouling while maintaining the high activity of biofilm. This study presents a novel ceramic-based ultrafiltration membrane functionalized with tourmaline nanoparticles to address this challenge. The incorporation of tourmaline nanoparticles enables the release of nutrient elements and the generation of an electric field, which enhances the biofilm activity on the membrane surface and simultaneously alleviates intrapore biofouling. The tourmaline-modified ceramic membrane (TCM) demonstrated a significant antifouling effect, with a substantial increase in water flux by 60 %. Additionally, the TCM achieved high removal efficiencies for contaminants (48.78 % in TOC, 22.28 % in UV₂₅₄, and 24.42 % in TN) after 30 days of continuous operation. The fouling resistance by various constituents in natural water was individually analyzed using model compounds. The TCM with improved electronegativity and hydrophilicity exhibited superior resistance to irreversible fouling through increased electrostatic repulsion and reduced adhesion to foulants. Comprehensive characterizations and analyses, including interfacial interaction energies, redox reaction processes, and biofilm evolutions, demonstrated that the TCM can release nutrient elements to facilitate the development of functional microbial community within the biofilm, and generate reactive oxygen species (ROS) on the membrane surface to the degrade contaminants and mitigate membrane biofouling. The electric field generated by tourmaline nanoparticles can promote electron transfer in the Fe(III)/Fe(II) cycle, ensuring a stable and sustainable generation of ROS and bactericidal negative ions. These synergistic functions enhance contaminant removal and reduce irreversible fouling of the TCM. This study provides fundamental insights into the role of tourmaline-modified surfaces in enhancing membrane filtration performance and fouling resistance, inspiring the development of high-performance, anti-fouling membranes.