Simultaneous removal of nitrogen and phosphorus nutrients from secondary effluent by magnetic resin containing two types of quaternary ammonium adsorption sites: Preparation, characterization, and application

The direct discharge of secondary effluent (SE) from wastewater treatment plants without proper nitrogen and phosphorus treatments can result in the eutrophication of landscape water bodies. The primary objective of advanced treatment should focus on the removal of NO3− and PO43− as the optimal approach. In this study, magnetic resin microspheres known as MGE (derived from the initials of the three organic monomers used, namely methyl methacrylate, glycidyl methacrylate, and 3,4-epoxy-1-butene) were successfully prepared through suspension polymerization. MGE incorporated two types of sites specifically designed for the removal of anionic nitrogen and phosphorus nutrients. The removal of NO3−, PO43−, and humic acid (HA) by MGE fit well with the pseudo-second-order kinetic and Freundlich adsorption isotherm models (R2 = 0.884–0.993 and 0.918–0.969, respectively). The removal efficiencies of ultraviolet absorbance at 254 nm, total nitrogen, total phosphorus, NO3−, PO43−, and total fluorescence in SE by MGE were 50.4 %, 20.9 %, 27.1 %, 21.5 %, 30.2 %, and 42.0 %, respectively, which were significantly higher than those achieved by commercially available MIEX® and D201. The molecular dynamic simulation results indicated that the increased removal of NH4+ by resin after adsorption of HA can be attributed to the aggregation effect of HA and NH4+ caused by H-bonds. The nitrogen and phosphorus indicators of the MGE effluent met the GB/T 18921-2019 water quality standard for scenic environmental use in China. MGE exhibited exceptional adsorption capacity and rapid achievement of adsorption equilibrium, making it a potential adsorbent for the removal of anionic nitrogen and phosphorus nutrients in engineering applications.