Phosphorus removal with zero-valent iron: Fixed-bed experiments with long-term monitoring and solid analysis

Abstract

Zero Valent Iron (ZVI) is considered a good media for contaminant removal in wastewater. Through batches and fixed-bed experiments, phosphate (P) removal performances of iron-based materials were studied. Three iron-based materials, with various grain sizes and compositions, were selected to fill columns in a reactive mix with sand, with two ratios (1 % and 10 % iron). After 300 days, the columns were dismantled and solid analyses performed on the remaining media. Over 50 % P retention was observed for the 1 % ZVI/sand ratio reactors for longer than 6 months. For the 10 % ratio, better performances were attained over a longer lifetime (above 70 % for 7 months). The P distribution was heterogeneous along the column since the activation of the layers were gradually influenced by both oxygen and P concentrations. Solid analyses showed that P was mostly bound to amorphous iron oxides (55 %), with a small percentage being linked to crystalline iron byproducts (10 %). >10 % of P was retained by calcium, highlighting its contribution to P scavenging. In considering the influence of these major parameters, an overview of P removal mechanisms through a continuous upflow fixed-bed was then proposed, that could be helpful for future P treatment reactor's design.