Continuous Phosphorus Removal From Retention Basin Water Using Modified Basic Oxygen Furnace Slag Under Controlled Superficial Velocity

To restore phosphorus (P) removal in aged basic oxygen furnace slag, the continuous P removal and breakthrough behaviors of thermally modified slag (TMS) and thermo-alkali-modified slag (TAMS) columns were evaluated across superficial velocities. In synthetic wastewater, both media exhibited kinetic breakthrough at 100 m/h from precipitate accumulation. At 50 m/h (1000 bed volumes; BV), TAMS (86.14% removal) maintained a 3.2-fold lower effluent P concentration than TMS, mitigating precipitate-induced kinetic breakthrough. In real urban retention basin water, a mixed bed (TMS:TAMS = 1:1) clogged prematurely at 50 m/h (333 BV). However, decreasing the velocity to 20 m/h (void hydraulic retention time = 17 s) restored effluent P below the limit of quantification under dry-weather conditions and sustained over 92% removal (effluent P ≤ 0.11 mg/L) under a ninefold higher wet-weather load (151.2 mg P). These findings provide superficial velocity guidelines to alleviate clogging during the treatment of urban retention basin water.