Determining which iron minerals in iron-enhanced sand filters remove phosphorus from stormwater runoff

Excess phosphorous is a water quality problem affecting storm runoff, rivers, and lakes in urban and agricultural settings throughout Minnesota, causing algal blooms, making lakes green, and negatively affecting fish and wildlife. More than 50 iron-enhanced sand filter basins have been installed throughout Minnesota since 2009 to remove phosphorous from water, and many more are scheduled for installation with costs ranging from $30k-$300k each. The physical and hydrological properties of iron-enhanced sand filters are well known, but their chemical properties are not (Table 1), and despite wide success, some iron-enhanced sand filter systems that are currently installed are not working effectively. There is an initiative by designers to secure a local source of iron with consistent chemical characteristics for more consistent filter results and to minimize substantial shipping cost, but any iron source needs to be tested for effectiveness prior to acquisition, and we currently do not know which chemical and mineralogical characteristics of iron are optimal for filter effectiveness and longevity.

We hypothesize that only certain iron minerals will remove phosphorous from water, and our proposed work is to determine which iron minerals make iron-sand filters work efficiently.

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