Stabilization of nutrients by alum (aluminum sulfate) is a relatively new area of research (USEPA, 2004b), and an area where a water utility can use their own treatment plant's residuals to help in source water protection from agricultural operations. Beneficial use through application of alum and ferric hydroxide water treatment residuals to agricultural land can provide an inexpensive disposal option for utilities and protect source water quality by binding to and reducing the transport of phosphorus (DeWolfe, 2003). The use of alum on poultry litter can help stabilize phosphorus to prevent its runoff to surface waters and leaching to ground waters.
Alum can be added to dry litter in poultry houses, typically between shifts of birds in the houses. The alum binds the phosphorus in the litter and makes it less soluble. Up to 90 percent less phosphorus may be solubilized in runoff from fields with alum-treated litter versus untreated litter (Walker, 2000). Alum also reduces ammonia gas emissions from the litter, which in turn improves bird health, increases weight gains and reduces mortality, thus saving the producer money. In fact, savings from these benefits may more than offset the cost of the alum (Walker, 2000).
DeWolfe (2006) evaluated the ability of different types of water treatment residuals to reduce loss of phosphorus from agricultural land, developed recommendations for utilities regarding use of their residuals, and will calibrated land application of residuals as a best management practice. The research found that each water treatment residual (WTR) has unique phosphorus binding potential based on the coagulant used, age of the WTR, and form of the WTR used (wet or dry). Blending WTRs with a high-phosphorus soil demonstrated reductions in both soil test phosphorus and soluble phosphorus. Simulated rainfall testing confirmed the ability of WTRs to reduce phosphorus in runoff for soils that are high in phosphorus and have also recently received organic material (e.g., poultry manure). The WTRs applied as liquid reduced phosphorus slightly better than when applied as dry material. WTRs blended with biosolids and poultry manure revealed substantial reductions in both soil test phosphorus and soluble phosphorus, and that the reduction was directly related to the amount of WTRs used. An ongoing related AwwaRF-sponsored research project on the “Effect of Long-Term Water Treatment Residuals-Biosolids Co-Applications on Native Soil Phosphorus” (AwwaRF Project #2995) is investigating both the long-lasting effects of a single water treatment residuals-biosolids co-application and the short-term impacts of a repeated application on soil phosphorus dynamics.