Molding of the ATP/5A/ZIF composite for simultaneous removal of nitrogen and phosphorus from wastewater: Investigation of adsorption mechanisms and performance evaluation

Abstract

In this study, a highly efficient composite composed of attapulgite (ATP), 5 A-zeolite (5 A), and zeolitic imidazolate framework-8 (ZIF-8), referred to as ATP/5 A/ZIF, was developed for the simultaneous removal of nitrogen and phosphorus. The solvent evaporation method was used to fabricate this composite for the removal of excess amounts of nitrogen and phosphorus from rural domestic wastewater discharges. To address the challenges of separating and recycling powdered adsorbents, a foaming agent was used to mold the ATP/5 A/ZIF composite. The resulting molded ATP/5 A/ZIF composite achieved simultaneous removal efficiencies of 70.93 % for ammonia nitrogen and 95.27 % for phosphorus. The surface properties and structural characteristics of ATP/5 A/ZIF were evaluated using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and Brunauer–Emmett–Teller analysis. To understand the mechanism of simultaneous nitrogen and phosphorus removal by ATP/5 A/ZIF, its adsorption kinetics, adsorption isotherms, and thermodynamics were studied. Phosphate was primarily removed through ligand exchange, electrostatic attraction, and hydrogen bonding, whereas ammonia nitrogen removal was driven by ion exchange, hydrogen bonding and dipole interactions. The molded ATP/5 A/ZIF composite exhibited excellent nitrogen and phosphorus removal efficiency, a low dissipation rate, high mechanical strength, and effective recyclability after adsorption. These attributes are significant because they effectively reduce production costs and significantly increase economic efficiency. Furthermore, scouring forces and water flow agitation during treatment can cause material loss or fragmentation. However, the mechanical strength and chemical stability of the molded composite were enhanced to withstand challenging water treatment conditions, making it highly suitable for nitrogen and phosphorus removal from rural wastewater discharges.