Batch laboratory scale experiments were conducted to investigate the removal of phosphate from aqueous and municipal wastewater samples by addition of Al-2(SO4)(3).18H(2)O, The effect of pH, Al-dose and initial phosphate concentration were assessed, Optimum phosphate removal, 51% for stoichiometric Al-dose, was observed at pH 6. However, a 151% excess of Al-dose was necessary for complete phosphate removal. Phosphate removal from municipal wastewater samples was slightly higher than that observed for the aqueous solutions. A chemical precipitation mathematical model was developed and tested with the available experimental data. The model considered 16 chemical equilibrium equations and the mass balance equations for aluminum and phosphorus. The chemical equilibrium equations included: (1) The co-precipitation of two solid phases containing aluminum and phosphorus. (2) The formation of 9 aluminum containing soluble complexes and polymers. (3) The formation of 2 aluminum and phosphorus containing complexes. (4) The 3 dissociation reactions of H3PO4. Because of the co-precipitation, the residual [Al3+] and [PO43-] were fixed and could be used to compute molar concentrations of all individual species in solution. Model predictions were in qualitative agreement with the experimental data.
