Enhanced Sand Filtration for Storm Water Phosphorus Removal

Of utmost concern in storm water treatment today is the removal of dissolved phosphorus. One method to effectively determine the phosphorus removal capacity of different sand filtration media is controlled, well mixed experiments called batch studies. Batch studies with an initial phosphorus concentration typical of storm water were conducted at the University of Minnesota on C 33 sand, calcareous sand, limestone, three blast oxygen furnace (BOF) by-products, aluminum oxide, and chopped granular steel wool for the removal of dissolved phosphorus from synthetic storm water runoff. After evaluation, our conclusions are: (1) C 33 sand alone can remove some dissolved phosphorus but batch studies are inconclusive about longevity of removal and pH affects; (2) calcareous sand and limestone removed significantly more dissolved phosphorus as compared to C 33 sand alone; (3) C 33 enhanced with aluminum oxide removed little, if any, additional phosphorus as compared to C 33 sand alone; (4) chopped granular steel wool removed significantly more phosphorus than C 33 sand alone after 10 hours of contact; (5) increases in mass of steel wool increased dissolved phosphorus removal; and (6) BOF by-products exhibited the most dissolved phosphorus removal, but produced alkaline pH conditions that exceed nationally suggested and state enforced standards. Based on these findings, sand filtration enhanced with steel wool, calcareous sand, or limestone has the potential to be practical and cost effective, but must be investigated further in laboratory column experiments or field sand filtration applications to ensure clogging or pH effects are not detrimental to the sand filter's functionality and to determine the long-term effectiveness of these enhancements.