Removal of phosphorus by the core-shell bio-ceramic/Zn-layered double hydroxides (LDHs) composites for municipal wastewater treatment in constructed rapid infiltration system

• Bio-ceramic/Zn-LDHs can be used efficiently for the phosphorus removal in CRIS.
• Compared natural bio-ceramic, SRP removal rate improved 49% by bio-ceramic/FeZn-LDHs.
• Coating Zn-LDHs on bio-ceramic improved the chemical effects in phosphate removal.

Constructed rapid infiltration systems (CRIS) are a reasonable option for treating wastewater, owing to their simplicity, low cost and low energy consumption. Layered double hydroxides (LDHs), novel materials with high surface area and anion exchange capacity, faced the problem of the application in CRIS due to the powdered form. To overcome this shortcoming, Zn-LDHs (FeZn-LDHs, CoZn-LDHs, AlZn-LDHs) were prepared by co-precipitation method and in-situ coated on the surface of the natural bio-ceramic to synthesize the core-shell bio-ceramic/Zn-LDHs composites. Characterization by Scanning Electron Microscope (SEM) and X-ray Fluorescence Spectrometer (XRFS) indicated that the Zn-LDHs were successful loaded on the natural bio-ceramic. Column tests experiments indicated that the bio-ceramic/Zn-LDHs efficiently enhanced the removal performance of phosphorus. The efficiently removal rates of bio-ceramic/FeZn-LDHs were 71.58% for total phosphorous (TP), 74.91% for total dissolved phosphorous (TDP), 82.31% for soluble reactive phosphorous (SRP) and 67.58% for particulate phosphorus (PP). Compared with the natural bio-ceramic, the average removal rates were enhanced by 32.20% (TP), 41.33% (TDP), 49.06% (SRP) and 10.50% (PP), respectively. Adsorption data of phosphate were better described by the Freundlich model for the bio-ceramic/Zn-LDHs and natural bio-ceramic, except for the bio-ceramic/CoZn-LDHs. The maximum adsorption capacity of bio-ceramic/AlZn-LDHs (769.23 mg/kg) was 1.77 times of the natural bio-ceramic (434.78 mg/kg). The effective desorption of phosphate could achieve by using a mixed solution of 5 M NaCl + 0.1 M NaOH, it outperformed the natural bio-ceramic of 18.95% for FeZn-LDHs, 7.59% for CoZn-LDHs and 12.66% for AlZn-LDHs. The kinetic data of the bio-ceramic/Zn-LDHs were better described by the pseudo-second-order equation. Compared the removal amount of phosphate by the natural bio-ceramic, the physical effects were improved little, but the chemical effects were enhanced for 112.49% for FeZn-LDHs, 111.89% for CoZn-LDHs and 122.67% for AlZn-LDHs. Therefore, the way of coating Zn-LDHs on the bio-ceramic efficiently improved the chemical effects in phosphate removal, supporting that it can use as potential substrates for the removal of phosphorus in CRIS.

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