Removal of phosphate from wastewater by steel slag with high calcium oxide column filter system; efficiencies and mechanisms study

BACKGROUND The discharge of wastewater with heavy loads of phosphorus (P) leads to eutrophication in natural water systems. The current work investigated the removal of P from synthetic wastewater via a slag filtration system with a high content calcium oxide (CaO) filter media (HCa) followed by treatment in an electric arc furnace (EAF). The pH, point of zero charge (PZC) and X‐ray fluorescence (XRF) of the HCa filter medium was studied. The removal of phosphorus was investigated in a designed vertical column filters in aerated HCa (AEF) and unaerated HCa (UEF) systems. Fourier transform infrared (FTIR), X‐ray diffraction (XRD) and scanning electron microscopy with energy dispersive X‐ray (SEM–EDX) analyses was implemented for studying the microstructure of HCa. RESULTS The results of XRF revealed that CaO ranged from 20.2 to 49.5%. The PZC for the HCa filter was recorded at pH 17.75. The highest efficiencies recorded were 94.65 ± 3.46% and 96.13 ± 2.75% at pH 3, and 93.70 ± 2.59% and 97.15 ± 1.59% at pH 5 for AEF and UEF, respectively. These findings indicated that AEF performed greater removal than UEF systems, possibly resulting from the presence of high Ca concentration in AEF, which plays an important role in the process of phosphorus removal. The main elements on the surface of HCa included oxygen, carbon, magnesium, Ca, aluminium and silicon. XRD analysis indicated that the precipitation of orthophosphate as Ca and Ca‐phosphates was the removal mechanism, which was confirmed by FTIR analysis. CONCLUSION These findings demonstrated the efficiency of HCa in removing P from wastewater. © 2020 Society of Chemical Industry