Performance of carbon nanotube-coated steel slag filter media for the removal of phosphorus and heavy metal in stormwater

Phosphorus and heavy metals in nonpoint pollutant sources cause significant problems in water systems, with a 22%-40% loading of the total pollutants in the four major rivers in Korea.No standard exists for phosphorus and heavy metals in device-type, nonpoint pollution abatement facilities in South Korea.Therefore, this study assessed the application of steel slag as a filter medium in these facilities.To increase its reactivity, the surface of slag was coated with carbon nanotubes (CNTs).The adsorption capacity of the CNT-coated slag was 1.36 and 1.83 times higher for phosphate and zinc, respectively, than that of the uncoated slag according to the adsorption isotherm.In addition, the adsorption of phosphate and zinc through both uncoated and CNT-coated slag followed pseudo-first order kinetics.In the cylindrical column test, during a 100-rainfall repetition test, the removal efficiency of phosphate, zinc, and copper were 66.3%, 78.1%, and 68.3%, respectively, by the uncoated slag, and 78.0%, 85.1%, and 70.0%, respectively, by the CNT-coated slag.These results show that CNT-coated steel slag is an attractive filter medium for the removal of phosphorus and heavy metals in a nonpoint pollution abatement system that reduces the overall operating cost by increasing the replacement cycle.