E. Coli Removal Utilizing Biochar Iron Sand Filters
Stormwater conveys bacteria such as E. coli to receiving waters, where contact can be a human health risk: ingestion of E. coli can cause various diseases, such as gastroenteritis, urinary tract infections and neonatal meningitis. Waters in many urban areas, such as the Twin Cities Metro Area, are frequently afflicted with chronic and acute E. coli impairment, as bacteria sources in these areas are myriad and diffuse –pet and wildlife waste, sanitary overflows and leakages - and options for reducing loads are limited. How do you effectively and economically address dangerous bacteria nutrients being conveyed to your impaired water or to your swimming beach? Because E. coli sources are diffuse, it is more practical and effective to address this issue downstream, rather than trying to mitigate its entry into waterways.
We will present four ways of using biochar amended iron-enhanced sand filters to reduce bacteria, nutrients, and suspended solids in urban stormwater runoff including the use of such filters in catch basins, filter boxes, and pond filter benches. In a first of its kind field application of research previously only conducted in the lab, the Shingle Creek Watershed Management Commission and the Coon Creek Watershed District have successfully achieved reductions of 70 percent to 90 percent of E. coli from stormwater, and have continued to do so over extended periods of study, even when incoming bacteria concentrations were extremely high. This was done while simultaneously reducing levels of both total and dissolved phosphorous in the water: a nutrient which can cause algal blooms and other impairments, harming aquatic organisms, and inhibiting recreation. The filters also demonstrated, on average, an 83 percent reduction in total suspended solids between the inflow and the outflow. This is an exciting finding with great potential. We installed biochar- and iron-enhanced sand filters in storm sewer catch basin inserts, stormwater pond sand filter benches, and two different types of in situ applications to reduce bacteria and nutrients in stormwater runoff. Combining biochar with the iron-enhanced sand, also provided the additional benefit of holding the biochar in place, preventing loss due to flotation. We will present three years of inflow and outflow monitoring data as well as lessons learned about designing and maintaining these types of filters. This data demonstrates that biochar- and iron-enhanced sand filters can be added to existing stormwater infrastructure or as standalone practices adds a powerful new tool to the urban stormwater toolbox.