Effect of Aluminum-Containing Amendments on Phosphorus Sequestration of Wastewater Treatment Wetland Soil
2009
Malecki-Brown, Lynette M. | White, John R.
Little research has been conducted on methods to restore the P removal capacity of older constructed wetlands, as P treatment capacity can decrease with time. We investigated the capacity of alum and three Al-containing alternatives (alum residual, polyaluminum chloride [PAC], and partially neutralized aluminum sulfate [PNAS]), at three rates (9, 18, and 36 g Al m⁻²) to reduce P concentrations. Water column pH of the alum treatment was significantly less than all other treatments, averaging 3.65 ± 1.12, while PAC (4.85 ± 0.96) and PNAS (4.21 ± 0.93) treatments had pH values significantly less than the alum residual and controls. Soluble reactive P decreased in the water column of all the treatments (−60.41 to −2.11 mg m⁻² d⁻¹). At all dosage rates, alum and PNAS were most effective at binding P, followed by PAC, while the alum residual was least effective. Significantly less P removal occurred in the 9 g Al m⁻² alum, PNAS, and PAC treatments than the higher Al dosages. Dosage was inversely related to microbial biomass and activity in the surface soil, suggesting short-term negative effects of chemical additions. Results suggest that a low-dosage Al amendment application to wetland soil can, in the short term, prevent release of P from organic soil into the water column as well as remove P from the water column. Long-term studies are needed, however, to verify P removal efficacy with time and the effects of continued applications on nutrient availability.
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