Enhancing urban river water quality in Indonesia using mineral wool: Long-term field performance, seasonal dynamics,...

Urban rivers in rapidly growing tropical cities face persistent pollution pressures and limited wastewater infrastructure, demanding scalable in-stream restoration approaches. This study presents the first long-duration, field-scale deployment of mineral wool (MW) in a tropical monsoon river system, evaluating pollutant attenuation and seasonal treatment dynamics in the Cikapayang River, Bandung, Indonesia. Two MW configurations were installed in cascade channels without pumping, chemical inputs, or hydraulic control, and monitored across wet and dry seasons. Water quality was assessed using 11 physical and chemical parameters and interpreted through four Water Quality Indices (PI, STORET, CCME-WQI, NSF-WQI) to benchmark regulatory and international assessment frameworks. MW achieved mean pollutant removal of 43.51 %, improving river status from heavily polluted to moderate/lightly polluted. Dry-season performance intensified due to longer hydraulic retention and mature biofilms, yielding up to 61.52 % COD and 50.28 % TN removal, while wet-season turbulence reduced residence time but retained stable performance. Microstructural imaging confirmed a transition from mineral-mediated filtration and cation exchange to biofilm-driven nitrification-denitrification. Among WQIs, CCME-WQI exhibited the highest sensitivity, improving from "very poor" to "poor-fair (44.24)", while PI offered more optimistic classifications. Findings demonstrate MW as an effective, low-energy, circular-material solution for decentralized urban river treatment under monsoon hydrology. This work bridges the gap between controlled experiments and real-river implementation, providing performance and assessment benchmarks for scalable nature-based interventions in developing regions. Future studies should address media longevity, regeneration, and hydrodynamic optimization.