Enhancing phosphate removal from wastewater by using polyelectrolytes and clay injection

Aluminum sulfate, alum, is a common chemical coagulant used for coagulation. Recently, polymers have been utilized in coagulation/flocculation processes for water purification. In this study, the ability of two organic polymers, tannin (natural polyelectrolyte) and AN913 (synthetic anionic polyelectrolyte), and clay to act as coagulant aids was tested, in the removal of phosphate from synthetic wastewater. Contaminants in synthetic waters were coagulated using alum, alum + clay, alum + tannin, alum + AN913, alum + tannin + clay and alum + AN913 + clay. Alum together with polymers as coagulant aids yielded a significant improvement in phosphate removal compared with alum alone, for initial phosphate concentrations of 5-15 mg/l PO43-. The use of clay and polyelectrolytes improved the efficiency of phosphate removal and lowered the required alum dose. Fourier transform infrared (FTIR) spectroscopy was used for the identification and characterization of the aluminum species formed during dephosphorization of the synthetic wastewater with and without tannin, AN913 and clay. Evidence from FTIR spectroscopy showed the formation of aluminum hydroxyphosphate, hydroxy-Al-tannate and aluminum complexes containing phosphorus, tannin and AN913. (C) 2003 Elsevier Science B.V. All rights reserved.