Optimization of phosphorus removal from agro-wastewater by iron desalinization treatment residue (Fe-DTR)

Phosphorus (P) is a non-renewable nutrient that needs recycling. Cowshed wastewater is P-rich, though efficient P recycling is required. We aimed to optimize the chemical-physical process of loading P in cowshed wastewater onto iron desalinization treatment residue (Fe-DTR), while explaining the interactions involved. We investigated the impact of adsorbent dosage, particle size, pH, and temperature on P adsorption capacity and kinetics. The highest adsorption occurred at pH 3 and 25 C-degrees (11,410 +/- 1 mg P kg(-1) Fe-DTR) after 3 h, significantly surpassing adsorption at pH 7 and 40 C-degrees (10,834 +/- 371 mg P kg(-1) Fe-DTR), improving P capacity compared to Langmuir S-max of 7260 mg P kg(-1). A probabilistic model called Design of Experiment (DOE) suggested that combining low pH and high temperature could enhance P adsorption. Lower pH likely increased adsorption by removing competing ligands, and higher temperature has probably led to endothermic behavior, reducing solubility of calcium/iron phosphate phases. The pseudo-second-order model best described the adsorption rate. The activation energy indicated stronger bonds at pH 3 (8082 J mol(-1)) compared to pH 7 (3970 J mol(-1)). Hence, optimal conditions for P loading onto Fe-DTR at environment temperature are pH 3, particle size distribution of 45-90 mu m, solid/liquid ratio of 5 g L-1, and loading time of 3 h, though, three of four models we tested indicated two stage adsorption, including rapid initial adsorption (<90 min), followed by slower second-stage adsorption. This research showcases the circular economy concept by efficiently repurposing two distinct waste streams to generate a valuable resource for P fertilizers.