Enhanced Sand Filtration for Storm Water Phosphorus Removal

Batch and column studies were conducted on several media to determine the most effective method to enhance the dissolved phosphorus retention capacity of C 33 sand filtration. This study found that C 33 sand alone could retain some dissolved phosphorus but its capacity was quickly exhausted and therefore required media enhancements to improve the phosphorus retention capacity. Batch studies evaluated calcareous sand, limestone, three blast oxygen furnace (BOF) by-products, aluminum oxide, and chopped granular steel wool and found that BOF by-products increased pH levels above EPA guidelines and aluminum oxide did not significantly retain phosphorus. Column studies determined that calcareous sand and limestone retained more phosphorus as compared to C 33 sand but their fine grain size clogged the filter very quickly. Steel wool also retained more phosphorus than C 33 sand and did not clog the filter. Additionally, cost estimates show that steel wool enhancement would increase construction costs by roughly 3–5%. Fine iron oxide particles from the steel wool were observed in the effluent from the columns but any phosphorus attached to these particles is of limited bioavailability. A mass balance model was developed to predict phosphorus retention capacity of steel wool enhanced sand filtration based on contact time, influent concentration, and sum of phosphorus mass retained. Based on the results of the study, it is evident that steel enhanced sand filtration is an effective solution for removing dissolved phosphorus from stormwater runoff.