Global water scarcity is a threat that can be alleviated through membrane filtration technologies. However, the widespread adoption of membranes faces significant challenges, primarily due to membrane biofouling. This is the reason why membrane modifications have been under increasing investigation to address the fouling issues. Antibacterial membranes, designed to combat biofouling by eliminating microorganisms, offer a promising solution. Within this study, flat sheet ultrafiltration (UF) membranes with integrated photocatalytic zinc oxide (ZnO) nanoparticles were developed, characterized, and assessed through filtration and fouling tests. The antibacterial properties of the membranes were conducted in static tests using Gram-negative bacteria—Escherichia coli—and natural tap water biofilm. The results demonstrated a notable enhancement in membrane surface wettability and fouling resistance. Furthermore, the incorporation of ZnO resulted in substantial photocatalytic antibacterial activity, inactivating over 99.9% of cultivable E. coli. The antibacterial activity persisted even in the absence of light. At the same time, the persistence of natural tap water organisms in biofilms of modified membranes necessitates further in-depth research on complex biofilm interactions with such membranes.

Membrane filtration is a safe and sustainable water treatment method; however, membrane fouling remains a major challenge that limits its broader application. Modified membranes for fouling mitigation have been extensively studied, including photocatalyst incorporation for organic matter degradation and biofouling control. However, no commercially available photocatalytic membranes exist to date, possibly owing to the lack of understanding of their properties. Furthermore, conventional microbiological test methods commonly used in membrane research are insufficient for accurately assessing membrane antibiofouling properties. Mixed-matrix dual-layer membranes with varying concentrations of zinc oxide nanoparticles were prepared and characterized using multiple testing approaches. Despite achieving >99.999% reduction in cultivable Escherichia coli, viability assays revealed that only half of the cells were dead, with the rest entering a viable but nonculturable (VBNC) state and forming microcolonies, resulting in misleading CFU-based results. Additionally, Pseudomonas aeruginosa biofilm formation was evaluated using fluorescence staining to assess extracellular polymeric substance (EPS) production. While P. aeruginosa survived and multiplied on the photocatalytic membranes, biofilm maturation was inhibited, with EPS protein production reduced by up to 84% compared with the unmodified reference.

Membrane in situ coating design using a filtration unit with lipase and chitosan recirculation, which results in chitosan polyelectrolyte coating and lipase crosslinking for lipid fouling layer hydrolysis. Membrane filtration is widely used in water treatment due to its high separation efficiency. However, membrane fouling remains a major challenge, limiting its global spread. Currently, fouling mitigation relies mainly on membrane cleaning. This study proposes a shift from fouling removal to prevention through enzymatic membrane biofunctionalization. Enzymes are used in cleaning-in-place as effective organic matter catalysts. Immobilizing them on the membrane is suggested to catalyze foulants before a stable fouling layer is formed. For a practical application, this study suggests a shift from membrane modification during the manufacturing process to modification in situ. Lipase from Candida rugosa was immobilized on self-prepared polyethersulfone flat-sheet membranes via crosslinking to a thin chitosan polyelectrolyte layer. Dynamic coating conditions using a filtration unit and the immobilization procedure were optimized, achieving enzymatic activity exceeding 300 U m−2 within 1 h of coating. Oil emulsion filtration experiments revealed a significant reduction in irreversible fouling, meaning that reversible fouling could be easily removed by crossflow rinsing. The nontoxic nature of the coatings indicated a potential suitability as substrates for controlled biofilm-based membrane systems in biological treatment applications. The proposed lipase biofunctionalized membranes show potential for advanced treatment of fatty wastewater through active lipid catalysis.