Efficient removal of nitrogen and phosphorus in aqueous solutions using modified water treatment residuals-sodium alginate beads.

A high-performance sorbent, modified water treatment residuals-sodium alginate beads (WTR-SA beads), was prepared through a series of salt and combined thermal roasting composite modification between water treatment residuals and sodium alginate. The properties of modified WTR-SA beads composites were characterized by SEM-EDS, FT-IR, XRD, and BET. The adsorption performance of WTR-SA beads was investigated in removing nitrogen and phosphorus from wastewater. Compared to the unmodified WTR, the removal efficiency of nitrogen and phosphorus onto the modified WTR-SA beads was increased from 22.34 and 77.13% to 95.14 and 98.31%, respectively. The adsorption capacities of nitrogen and phosphorus onto the modified WTR-SA beads were reach a maximum of 2.52 mg/g and 6.45 mg/g, respectively. The adsorption behavior can be well described using a quasi-second-order kinetic model and Langmuir isotherm model. The thermodynamic properties of nitrogen adsorption indicated that the adsorption was spontaneous and exothermic. On the contrary, the adsorption process of phosphorus is an endothermic reaction. The adsorption of nitrogen by modified WTR-SA beads is mainly carried out through ion exchange and hydroxyl complexation, and ion exchange plays a major role in it. While, the adsorption of modified WTR-SA beads on phosphorus is affected by three actions: ligand exchange, chemical precipitation, and ion exchange, which ligand exchange is the main effect. Based on these results, it can be concluded that the modified WTR-SA beads are a high efficiency adsorbent for removing nitrogen and phosphorus from domestic and industrial wastewater.