Efficient Phosphorus capture from treated sanitary wastewater using a waste-derived SiO2@FeOOH composite: Robustness, Ca2+ interactions, and recovery perspectives

Phosphorus uptake and recovery from sanitary wastewater have been considered a promising approach to producing more sustainable fertilizers, in addition to reducing environmental damage caused by the discharge of this nutrient into water streams. In this study, the Phosphorus adsorption/desorption dynamics exhibited by a tailored SiO₂@FeOOH adsorbent, produced using quartz sand waste and Fe derived from the acid dissolution of scrap iron, were examined. The adsorbent’s behavior, robustness, and interaction with Ca²⁺ ions in simulated treated sanitary wastewater were systematically investigated. As a result, the behavior of the adsorbent under controlled conditions was successfully modeled, and relevant interactions between the material and Ca²⁺ ions were identified under simulated conditions. The performance of the adsorbent was not affected by the presence of nitrate, carbonate, sulfate, ammonium, fluoride, and humic substances in the simulated media. Additionally, the composite can adsorb humic substances and Phosphorus simultaneously, without interfering with its Phosphorus adsorption capacity. In simulated treated wastewater, the adsorption of the nutrient was enhanced in the presence of Ca²⁺; however, the formation of insoluble Ca/P deposits on the adsorbent surface significantly changed the adsorption dynamics and disturbed the recovery of Phosphorus using the usual alkaline desorption method. The adsorbent exhibited a robust Phosphorus adsorption capacity as high as 40 mg P/g in simulated treated wastewater, showing clear potential for Phosphorus uptake in Wastewater Treatment Plants. Based on the experimental evidence, future perspectives on the final disposal of the spent adsorbent were also discussed within a circular economy framework.