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Journal of Water Supply: Research and Technology—AQUA Vol 58 No 1 pp 1–10 © IWA Publishing 2009 doi:10.2166/aqua.2009.017

Phosphorus adsorption on water treatment residual solids

Meaghan K. Gibbons, Md. Maruf Mortula and Graham A. Gagnon

Department of Civil and Resource Engineering, Dalhousie University, Halifax, Nova Scotia, B3J 1X1, Canada Tel.: +1 902 494 3268 Fax:+1 902 494 3108 E-mail: graham.gagnon@dal.ca
Department of Civil Engineering, American University of Sharjah, Sharjah, PO Box, 26666, UAE


ABSTRACT

The treatment and disposal of water treatment plant residual solids has become an increasingly important environmental priority for drinking water utilities. This study examines water treatment residual solids (WTRSs) from four North American water treatment plants to determine the role that coagulant types play in phosphate adsorption by the residual solids. In total, two alum residual solids (one solid from a plant that has a raw water with low alkalinity and one solid from a plant that has a raw water with high alkalinity), one lime residual solid and one ferric residual solid were used in batch adsorption experiments with deionized water at a pH of 6.2±0.2 and secondary municipal wastewater effluent at a pH of 6.8. Langmuir isotherm modeling showed that ferric residuals had the highest adsorptive capacity for phosphate (Qmax=2,960 mg/kg), followed by lime (Qmax=1,390 mg/kg) and alum (Qmax=1,110 mg/kg and 1,030 mg/kg) for adsorption experiments with P-spiked deionized water. Of the two alum residuals, the residual with a higher weight percent of metal oxides had a higher adsorptive capacity. The ferric residuals were less affected by competing species in the wastewater effluent, while the lime and alum residuals had a higher rate of phosphate removal from the deionized water compared to the wastewater effluent. Overall, ferric water treatment residuals were the best adsorbent for phosphate adsorption, followed by lime and alum residuals.

Keywords: adsorption; alum sludge; Langmuir isotherm; phosphorus treatment; water treatment residual solids


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