Barr has an established history of using sand and active-media filters to remove dissolved pollutants, such as phosphorus, from stormwater runoff. Metals removal is a new application of this technology—using finely shredded scrap iron that rusts to ferric oxide in a stormwater treatment filter and then binds to both phosphorus and dissolved metals.
Barr designed and conducted a study for the National Cooperative Highway Research Program to field test the effectiveness of ferric-oxide media in sand filters for removing dissolved metals—such as copper, lead, zinc, nickel, and arsenic—from highway runoff. The study’s goals were to better understand how ferric-oxide filtration works; determine the chemical, physical, and hydrologic factors that affect performance; and identify metals that could be readily removed given a range of environmental and chemical conditions. Longevity and life-cycle costs were also quantified. The monitoring and sampling program was complex. Continuous measurement of flow, water level, pH, and dissolved oxygen for each treatment cell, along with aquatic chemistry modeling, helped researchers identify conditions conducive to metals removal. Quality assurance and sampling and analysis plans were developed based on U.S. EPA guidelines.
Using study results, Barr produced design, maintenance, and siting guidelines for ferric-oxide sand-filtration systems, which require less maintenance than mechanical systems. Filtration-media costs can be further reduced by using repurposed industrial byproducts. The study will likely have relevance outside of the transportation industry, with applications for cities, water management organizations, regulatory agencies, and industrial markets including mining, fuels, power, renewable energy, and manufacturing.