A Method for Determining the Phosphorus Sorption Capacity and Amorphous Aluminum of Aluminum-Based Drinking Water Treatment Residuals
- E. A. Dayton * and
- N. T. Basta
A high amorphous aluminum or iron oxide content in drinking water treatment residuals (WTRs) can result in a high phosphorus (P) sorption capacity. Therefore, WTR may be used beneficially to adsorb P and reduce P loss to surface or ground water. The strong relationship between acid ammonium oxalate–extractable aluminum (Alox) and Langmuir phosphorus adsorption maximum (Pmax) in WTR could provide a useful tool for determining Pmax without the onus of the multipoint batch equilibrations necessary for the Langmuir model. The objectives of this study were to evaluate and/or modify an acid ammonium oxalate extraction of Alox and the experimental conditions used to generate P adsorption isotherms to strengthen the relationship between Alox and Pmax The oxalate extraction solution to WTR ratio varied from 40:1, 100:1, and 200:1. Batch equilibration conditions were also varied. The WTR particle size was reduced from <2 mm to <150 μm, and batch equilibration was extended from 17 h to 6 d. Increasing the solution to WTR ratio to 100:1 extracted significantly greater Alox at levels of >50 mg Al kg−1 No additional increase was found at 200:1. Reducing WTR particle size from <2 mm to <150 μm increased Pmax 2.46-fold. Extending the equilibration time from 17 h to 6 d increased Pmax by a mean of 5.83-fold. The resulting empirical regression equation between the optimized Alox and Pmax (r 2 = 0.91, significant at the 0.001 probability level) may provide a tool to estimate the Pmax of Al-based WTR simply by measuring Alox The accurate determination of WTR Pmax and Alox is essential in using WTR effectively to reduce P loss in runoff or to reduce the solubility of P in agricultural soils or organic waste materials (biosolids, manure).Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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