Effects of Filtration Velocity of Sand Filter Beds on Microparticulate and Natural Organic Matter Removal from River Water

River water often contains micropollutants such as microparticulates (including colloids and microplastics, MPs) and natural organic matter (NOM). Current decentralized water treatment systems, typically consisting of coagulation-sedimentation and rapid sand filtration with or without granular activated carbon, are generally inefficient in removing MPs and NOM. To evaluate the performance of sand filter (SF) beds in removing these micropollutants, batch and continuous experiments were conducted to investigate the effects of filtration velocity. SF beds operated at filtration velocities between 1.5 and 3.0 m/h achieved high removal efficiency (> 70%) for microparticulates (turbidity and MPs) but showed low efficiency (< 5 %) for NOM (total organic carbon, 2-methylisoborneol, and geosmin). However, headloss increased with filtration velocity due to pore clogging by microparticulates. When the filtration velocity increased from 1.5 to 3.0 m/h, the headloss at 3.0 m/h was approximately twice that at 1.5 m/h. These results indicate that SF beds should be operated at lower filtration velocities to prolong filtration time and enhance the removal efficiency for microparticulates and NOM.