Soluble Phosphorus Removal Through Adsorption on Spent Alum Sludge

• Published in: Environmental technology Vol. 27; no. 10; pp. 1081 - 1088
• Main Authors: Georgantas, D. A., Matsis, V. M., Grigoropoulou, H. P.
• Format: Journal Article
• Language: English
• Published: London Taylor & Francis Group 01.10.2006; Selper
• Subjects: Adsorbents; Adsorption; Alum; Alum Compounds - chemistry; Aluminum; Applied sciences; Athens; Chemical engineering; Chemisorption; Diffraction; ELOVICH; Exact sciences and technology; General purification processes; Hydrogen-Ion Concentration; Isotherms; Kinetics; LAGERGREN; LOW COST ADSORBENT; Mathematical analysis; ORTHOPHOSPHATE; Phosphates - chemistry; Phosphorus; Phosphorus - analysis; Phosphorus - chemistry; Phosphorus removal; Pollution; PSEUDO-SECOND-ORDER KINETICS; Sewage - chemistry; Sludge; Solubility; Sorption; Waste Disposal, Fluid - methods; Waste water; Wastewaters; Water Purification - methods; Water treatment and pollution; X-rays; Chemisorption; Second order; pseudo-second-order kinetics; Lagergren; Orthophosphate; Adsorption isotherm; Phosphorus; Elovich; X ray diffraction; Waste water; Sorption; Adsorption; pH; low cost adsorbent; Kinetics; Aluminium sulfate
• ISSN: 0959-3330; 1479-487X
• DOI: 10.1080/09593332708618726

In the present study freshly precipitated spent alum sludge [15-75 mg Al l −1 ] and alum [3-15 mg Al l −1 ] were tested and compared for their efficiency to remove phosphorus in synthetic wastewater [10mg P l −1 , 25°C, pH=6] and it was proven that pure alum is much more efficient at phosphorus removal than the spent alum sludge. The effect of the pH on phosphorus removal efficiency was studied and it was proven that maximum orthophosphate removal is achieved in pH values 5-6 in both cases, alum and spent alum sludge, although alum is efficient in a wider pH range (4-7). The effect of aging [up to two months at 25 ° C] on the efficiency of the spent sludge to remove phosphorus in synthetic wastewater was studied and it was proven that this efficiency is decreased through aging (up to 20% for 2 months aging). X-ray diffraction was used in order to examine whether this decrease is caused by changes in the structure of adsorbent and a mechanism was proposed to explain the above changes. Kinetics was investigated in the case of fresh and aged spent alum sludge and the pseudo-second-order chemisorption rate equation fits satisfactorily the experimental data [k: 0.286-1.048 g mmol −1 min −1 , at 23-26°C]. Finally, equilibrium was studied for fresh and aged spent alum sludge and the Freundlich isotherm fitted best the experimental data suggesting heterogeneous sorption [K F =14.4-19.7, N: 0.13-0.20].