Antibacterial efficiency of composite nano-ZnO in biofilm development in flow-through systems

Biofouling and its control is an acute problem in all water-flowing systems. Inorganic nanoparticles (np) such as zinc oxide (ZnO) exhibit strong antibacterial activities on a broad spectrum of bacteria even when mixed within polymers. Most research until now tested the antibacterial ability only in static conditions. The current research studied the ability of ZnO np to suppress bacterial attachment and biofilm development under flowing conditions, either embedded in polymethyl methacrylate (PMMA) or entrapped in polyacrylamide gel. The composite ZnO np films were characterized by high resolution- scanning electron microscopy and energy-dispersive X-ray spectroscopy, and their antibacterial abilities were evaluated using inhibition zone in agar plates and direct contact in liquid media. In all cases studied, bacterial adhesion was significantly prevented, while the control sample showed biofilm development. Interestingly, a lower antibacterial activity was found in all cases under flowing conditions as compared to static conditions. In batch conditions, it was found that the antibacterial mechanism is based on reactive oxygen species release from the ZnO np. A composite ZnO-PMMA film was designed to mimic a feed spacer with antibacterial abilities in a membrane separation process, and the biofilm development was evaluated. The composite feed spacer displayed promising ability in delaying biofilm development in membrane filtration trials.