Low cost and effective phosphorus adsorbents are required for the treatment of small or decentralized wastewater systems. The goal of this study was to examine phosphorus adsorption on different low-cost media. Bone char and oven dried alum sludge had the highest Freundlich adsorption constants (K d ) of 1.031 and 0.484, respectively. Maximum adsorption density from the Langmuir isotherm plot was 0.674 mg P g −1 for oven dried alum sludge and 1.787 for air dried alum sludge. pH levels at equilibrium were close to 7 for various dried alum sludge. Experiments conducted at 16 g/L of adsorbent on secondary municipal wastewater showed that all types of dried alum sludge and bone char were the most effective adsorbents of phosphorus. pH levels for oven and air dried sludge were in the range of 6.5-7, whereas the blast furnace slag and cement kiln dust exceeded a pH of 9. Consequently further work was recommended for water plant residuals.

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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 (Q max ¼ 2,960 mg/kg), followed by lime (Q max ¼ 1,390 mg/kg) and alum (Q max ¼ 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.

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