Phosphorus and nitrogen removal from water using steel slag in soil-based low-impact development systems

This study applied waste steelmaking slags [including basic oxygen furnace slag and electric arc furnace slag] in a multi-soil-layering system for phosphorus and ammonia nitrogen removal from domestic wastewater. In the multi-soil-layering system, the slags were replaced in the soil mixture block layers (in brick-like patterns) or the permeable layers. For water feed containing approximately 20 mg/L of total phosphorus and 12 mg/L of ammonia nitrogen, the best phosphorus and ammonia nitrogen removal efficiencies of 93% and 84%, respectively, were achieved within 5 h of reaction. Mixing 25% basic oxygen furnace slag in the system provided a >85% phosphorus removal efficiency, especially in the soil mixture block layers. The phosphorus precipitation activated by released iron ions was the dominant mechanism rather than phosphorus adsorption onto zeolite/ soil. An iron content of approximately 10% in the soil mixture block layers and permeable layers contributed to phosphorus removal efficiencies of 43% and 86%, respectively. Zeolite in the permeable layers was more helpful than gravel for reducing pollutants. This study shows that using steel slags is suggested with the inherent characteristics of the media in the soil-based low impact systems.