Developing upflow filters operated in a cascade sequence to compare two green sorption media for phosphorus removal

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Finding solutions to treat stormwater runoff and wastewater effluent that contain phosphorus is an important effort due to the potential harmful algal bloom impacts on both human health and the environment, such as red tide in coastal regions, eutrophication of waterbodies, and fish kills. However, many of the remaining phosphorus reserves are becoming depleted. Finding low-cost, energy-efficient, and low-maintenance solutions that incorporate green sorption media (GSM) mixed with natural and recycled materials to treat nutrient-laden water, with potential for recovery, is of critical importance for sustainable material development. Biochar and zero-valent iron (ZVI) have received significant attention as low-cost, low-impact adsorbents for the removal of heavy metals, pathogens, and nutrients due to their ability to aid in structural support and reasonable removal efficiencies in GSM. In this study, phosphorus removal efficiencies were studied using two new recipes of GSM within a unique passive cascade upflow filtration system. The two new GSM include zero-valent iron and perlite green environmental media (ZIPGEM) composed of 85% sand, 5% clay, 5% ZVI, and 5% perlite by volume, and biochar zero-valent iron and perlite green environmental media (BIPGEM) containing 80% sand, 5% biochar, 5% clay, 5% perlite, and 5% ZVI by volume. Results indicate that the ZIPGEM-based filtration system achieved an average removal of 78.9% to 97.9% in the initial 60-min to 300-min range, whereas BIPGEM exhibited an average 67.1% to 86.9% removal during this same time interval. At the time of shutdown as a system, BIPGEM showed an average 52.8% removal at the 5480-min mark, and ZIPGEM exhibited an average 69.1% removal at the 11,180-min mark. After examining three isotherm models, the dose-response model estimated the adsorption capacity of ZIPGEM as 6.5 mg·g−1. Further comparison of the material structures and compositions of both raw and spent media samples using X-ray diffraction, X-ray fluorescence spectrometry, and a scanning electron microscope helped confirm part of the removal mechanisms.