Seawater reverse osmosis (SWRO) membrane systems face inevitable performance decline due to biofouling, which imposes significant economic costs, accounting up to 25 % of water production costs in desalination plants. Current industry practices primarily rely on chemical cleaning treatments to restore membrane performance. However, these methods involve substantial expenses related to chemical acquisition, storage, and transportation, extended plant downtimes, and premature membrane replacement due to reduced lifespan. Additionally, the disposal of chemical waste raises serious environmental concerns. Micro-nano bubbles (MNBs), consisting of gas-filled cavities (from <1 μm to 5 μm in diameter), have emerged as a promising alternative for biofouling control. This study evaluates the performance of the air-filled (AMNBs) and CO2-nucleated bubbles (N_CO2) as curative cleaning-in-place (CIP) treatments and preventive daily treatments under conditions representative of SWRO systems. Using membrane fouling simulators (MFSs) and pressure drop as a performance indicator, curative AMNBs, and N_CO2 treatments achieved 49 %–56 % pressure drop recovery, comparable to conventional chemical cleaning (51 %) and significantly outperforming hydraulic flushing (24 %). Optical coherence tomography (OCT) imaging and biomass analyses confirmed these findings, revealing effective biofilm removal due to MNB's action. Preventive treatments demonstrated that Nucleated CO2 bubbles delayed performance decline by 123 %, AMNBs by 95 %, and hydraulic flushing by only 15 % compared to controls. OCT imaging and membrane biomass analysis confirmed reduced biofilm growth and biomass accumulation in bubble-treated systems. These results indicate that MNB technologies hold great potential as a sustainable and eco-friendly alternative to chemical cleaning for biofouling management in SWRO systems.

Membrane modules for seawater desalination are becoming increasingly important for obtaining clean water with the rising global water scarcity. The productivity of membrane modules is compromised by biofouling on the membrane and feed spacer. Biofouling development can be mitigated by modification of the spacer or membrane surface. The purpose of the present study is to evaluate the impact of surface-modified feed spacers on the cleaning performance of spiral-wound membrane filtration systems. After cold-plasma treatment, the feed spacers were modified with various combinations of polydopamine (PDA) and silver nanoparticles (AgNP). To compare the cleaning performance of the modified and unmodified spacers, membrane fouling simulators containing nanofiltration membranes and feed spacers were tested under industrially representative conditions: two full cycles involving biofilm development followed by cleaning-in-place (CIP). The modified spacers significantly improved the CIP efficiency when compared with that of the unmodified feed spacer. The highest CIP efficiency was obtained for the PDA–AgNP-coated spacers, which removed >90 % of the biomass. The PDA layers remained undetached during the CIP process, and the amounts of AgNP decreased without affecting the CIP effectiveness during consecutive operational cycles. The results demonstrate that CIP should be included in biofouling tests to evaluate the full potential of surface modifications and suggest that hydrophilic and biocidal spacer surface coatings can significantly improve the CIP effectiveness, thereby considerably reducing the CIP frequency and operational costs.