Phosphate Removal from Digested Sludge Supernatant Using Modified Fly Ash
The removal of phosphate in digested sludge supernatant by modified coal fly ash was investigated in this study. Modification of the fly ash by the addition of sulfuric acid could significantly enhance its immobilization ability. The experimental results also showed that adsorption of phosphate by the modified fly ash was rapid with the removal percentage of phosphate reaching an equilibrium of 98.62% in less than 5 minutes. The optimum pH for phosphate removal was 9 and the removal percentage increased with increasing adsorbent dosage. The effect of temperature on phosphate removal efficiency was not significant from 20 to 40 °C. X‐ray diffraction and scanning electron microscope analyses showed that phosphate formed an amorphous precipitate with water‐soluble calcium, aluminum, and iron ions in the modified fly ash.
Effective Treatment of Nutrients by Adsorption onto the Surface of a Modified Clay and a Toxicity Evaluation of the Adsorbent
A pure clay ball and surface-modified clay ball were investigated to remove phosphate from synthetic wastewater; phosphate causes eutrophication in hydro-ecological systems. Adsorption tests of phosphate from aqueous solutions onto two types of adsorbents were conducted. The maximum phosphate adsorption capacities of the pure and surface-modified clay ball were found to be 0.084 and 8.869 mg/g, respectively. In a fixed-bed column packed with surface-modified clay balls, the first breakthrough of phosphate appeared after approximately 4000 min. In addition, the phosphate adsorbed on the surface-modified clay ball was effectively desorbed using a 1 M zirconium sulfate solution, and the adsorbent was regenerated for four adsorption and three desorption cycles by maintaining the adsorption capacity at the value before regeneration. X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX), and Brunauer-Emmett-Teller (BET) analysis method were performed to reveal the characteristics of the surface-modified clay ball. Cytotoxicity experiment was conducted on the developed adsorbents, and as a result, these showed low cytotoxic effect on the human cells. These results indicated that the surface-modified clay ball, due to the low cost, high adsorption capacity, and non-toxicity, has the potential to be utilized in the cost-effective removal of phosphate from aqueous solutions.
The adsorption of protolyzable anions on hydrous oxides at the isoelectric pH
The adsorption of two protolyzable anions (phosphate and arsenate) on a variety of hydrous oxide surfaces (γ-Al2O3, amorphous Al(OH)3, anatase, and cryptocrystalline Fe(OH)3) is studied as a function of the isoelectric pH (pHiep) of the combined oxide-adsorbate system. The relationship between the amount of adsorption (Γ) and the pHiep is interpreted in terms of proton dissociation occurring at, or very near, the solid/solution interface. A linearized adsorption isotherm at the pHiep is used to determine maximum adsorption (Γmax) and chemical free energy of adsorption.