Simultaneous adsorption study of ammonium and phosphate by ZnFe-layered double hydroxide (ZnFe-LDH)-modified adsorbents.

Abstract

Background Trace amounts of nitrogen and phosphorus can easily trigger eutrophication damage in surface water, while cost-effective adsorption treatment is in prospect for clearing these pollutants simultaneously and efficiently. In this study, engineered adsorbents decorated with ZnFe-LDH by alkaline coprecipitation (3-6 mm, with modified ceramsite as CZF and modified volcanic rock as VZF) were prepared for NH 4 + and H 2 PO 4 - co-adsorption from aqueous solutions.Results Coexisting ions showed great effects on phosphate adsorption, especially Ca 2+ and CO 3 2- , and humic acid exhibited only a limited shielding impact on co-adsorption properties. Though comprehensive tests presented that the maximum captured amount of ammonium and phosphate occurred at pH 7, the isotherm and kinetic results suggest that two adsorbents preferentially adsorbed each pollutant. Specifically, the maximum uptake quantity of NH 4 + (15.55 mg-N g -1 ) and H 2 PO 4 - (11.21 mg-P g -1 ) were achieved by VZF and CZF, respectively, and controlled by physisorption and chemisorption distinctively, revealing that contaminants were cleared in disparate ways. Performances of seven consecutive adsorption/desorption cycles using 5% NaOH regenerant suggested that CZF retained 71.9% of PO 4 - removal efficiency, and VZF retained 47.9% of the NH 4 + adsorption rate, implying the strong reusability of ZnFe-LDH-modified adsorbents. A dynamic study has assessed that with 1 kg of combined modified adsorbents, approximately 527 L of polluted runoff flow could be continuously treated to below the National limits within one adsorption cycle.Conclusion Comparing with other parallel adsorbents, ZnFe-LDH-modified adsorbent is promising in eliminating eutrophication due to their superior capacity, stability, renewability, and non-toxicity.

Nutrient Recovery for Fertilizer Production and Wastewater Treatment for a Circular Economy

“…Kinetic Model Parameters of the Adsorbents for Nutrients These adsorption capacities are more than half achieved by using RWW due to the competition between cations found in the WW 40,41 and the interference of adsorption sites by suspended particles. 41 A similar phenomenon was also found in a study by Liu et al, 42 where the ammonium breakthrough capacity was 2.4 mg of NH 4 + -N/g, which was barely half of the capacity found using synthetic solutions.…”

“…The adsorption capacity of CMLDH-HAP-N for NH 4 + -N remained constant over pH 2–6; after that the adsorption capacity decreased with the increasing pH resulting from the formation of dissolved OH – and CO 3 2– complexes, supported by the findings of pH pzc . Conversely, when the pH rose, the P adsorption capacity increased. − Adsorption dosages from 1 to 5 g/L reduced the adsorption capacities while increasing the removal efficiencies of NH 4 + -N and P (Figure S5D). One possible explanation for the reduced adsorption capacity at higher dosages could be unsaturated adsorption sites indicating that excess CMLDH-HAP might limit the available binding sites.…”

“…Following the adsorption of NH 4 + -N and P, the C–C/C–H/CC functional group reduced but −C–O and −CO rose. This implies that CMLDH-HAP stimulates −COO– and M–O– chemical bonding and electrostatic attraction to ammonium . Furthermore, CMLDH-HAP can exchange ligand between hydroxyl and PO 4 2– , producing elements, i.e., R–H 2 PO 4 and [(R–OPO 3 H) 2 Ca] .…”