In-situ ultrasonic treatment for effective clogging mitigation in sand filters

Sand filtration systems are cornerstone technologies in water treatment, yet they frequently suffer from clogging due to particle and biofilm accumulation, compromising efficiency and escalating maintenance demands. Ultrasonic treatment has shown significant potential in mitigating the clogging of filtration systems; however, most existing studies have focused predominantly on its applications in ultrafiltration and microfiltration. The potential of ultrasonic treatment in sand filtration remains largely unexplored. This study investigates the effectiveness and underlying mechanisms of in situ ultrasonic treatment (20–40 kHz) for reducing substrate clogging in sand filters. Results indicate that intermittent continuous ultrasound application delays clogging progression, with the 40 kHz treatment at 60 kW/m 2 achieving the best performance. Conversely, pulsed treatment at 28 kHz and 60 kW/m 2 was most effective in restoring permeability in sand filters, due to an optimal balance of cavitation intensity and stability. Ultrasonic treatment promoted particle disaggregation, reduced aggregate size, altered surface charge, and oxidized organic matter, thereby enhancing filter permeability. The approach was particularly effective against clogging caused by inorganic particles and showed high performance in treating clogging influenced by organic matter. Intermittent continuous ultrasound outperformed pulsed treatments in systems with high organic content, attributed to enhanced release or degradation of organic compounds. However, filters clogged by large particles and high volatile solids content exhibited limited recovery, suggesting that ultrasonic treatment is more effective for clogging dominated by small, inorganic particles. These findings highlight ultrasound as a sustainable and effective strategy for mitigating clogging in sand filtration systems. • Continuous ultrasound application delays clogging progression. • Pulsed ultrasound effectively restored permeability of clogged sand filter. • Ultrasound effectively mitigated clogging induced by fine inorganic particles. • Ultrasound promoted organic clog matter release or degradation.