Effect of aluminum-containing amendments on phosphorus sequestration of wastewater treatment Wetland soil
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.