Membrane water recovery in swimming pools: effectiveness, challenges and development perspectives

Swimming pools, as vital elements of public infrastructure, are important consumers of water and sources of washings, graywater, and domestic sewage. Maintaining strict hygiene standards while addressing increasing water scarcity and circular economy requirements necessitates advanced water recycling solutions. Although membrane technologies, such as ultrafiltration, are well established in municipal and industrial settings, their extensive deployment and long-term study in recreational facilities remain rare. Few studies offer a holistic perspective that integrates hydraulic performance monitoring with advanced analysis of membrane structure and composition throughout real operational periods. This research addresses this gap by evaluating a full-scale ultrafiltration system in one of Europe's largest indoor water parks. The system uses polyvinylidene fluoride (PVDF) membranes to treat washings and shower water. The study includes multi-parameter water quality assessments (physicochemical and microbiological), long-term hydraulic monitoring (up to 36 months), and detailed membrane characterization using scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS) to analyze fouling mechanisms and deterioration pathways. The results demonstrate substantial reductions in contaminants: chemical oxygen demand (COD) from 111 to 9 mg O₂/L, biological oxygen demand (BOD) from 26 to 2 mg O₂/L, turbidity by 95% and total organic carbon (TOC) by more than 90%. Under constant transmembrane pressure (0.75 bar), membrane flux decreased from 15 to 5 m³/h over 12 months due to progressive fouling. Analysis revealed stratified sediments, residual coagulants, oxidative membrane changes, and partial defluorination related to chlorine disinfection. These findings highlight the need for optimized operation and cleaning to ensure long-term membrane efficiency and sustainability.