Preferable Adsorption of Nitrogen and Phosphorus from Agricultural Wastewater Using Thermally Modified Zeolite–Diatomite Composite Adsorbent

Abstract

Nitrogen and phosphorus adsorbents are widely used to mitigate agricultural non-point source pollution. However, research on adsorbents mainly involves studying chemical adsorption properties, and analyzes of the effects of adsorbent on pollutant removal has not considered the surface morphology of the adsorbent or the surface distribution of pollutants. In this study, we focus on the surface morphology of the adsorbent and the surface distribution of contaminants while examining chemical adsorption properties. The crystal composition of the adsorbent was evaluated by x-ray diffraction (XRD) characterization. Kinetic adsorption data and adsorption isotherms demonstrated that thermally modified zeolite exhibits better nitrogen adsorption. The optimal removal of nitrogen and phosphorus by thermally modified zeolite and diatomite occurred at a 3:2 ratio, reaching a removal rate of 92.07% and 84.61%, respectively. The potential adsorption mechanism of a composite adsorbent for nitrogen and phosphorus capture was investigated by Fourier transform infrared spectroscopy. Scanning electron microscopy mapping, grey image recognition, and gradient recognition confirmed a relationship between the surface morphology of the adsorbent and the distribution of surface pollutants. The larger the surface of the gradient, the more uneven it is, the more nitrogen and phosphorus sites are adsorbed on the surface, and the more nitrogen and phosphorus are adsorbed. These results suggest that thermally modified zeolite/diatomite can serve as a promising adsorbent for nitrogen and phosphorus removal in practical applications.

Keywords

• composite adsorbent
• thermally modified zeolite
• diatomite
• sem mapping
• grey image recognition
• gradient recognition