Iron-sand Filters

How steel wool helps to clean water

Ten years ago, Andy Erickson was struggling with the challenge of how to protect lakes and rivers from stormwater pollution. When it rains, water hits rooftops, parking lots and streets, picking up dirt, nutrients, heavy metals and other pollutants along the way. By the time the runoff flows into wetlands, lakes and streams, it is filthy and contaminated. Fish and other wildlife suffer, algae grows thick during the summer, and people can no longer swim, fish and recreate. Stormwater management has improved over the years, but Erickson, a research fellow with the University of MN, St. Anthony Falls Laboratory, felt certain that innovative technologies were needed to help cities and watershed organizations better fight the problem. So, he set up an experiment in which he mixed a variety of common materials with sand and measured how well these enhancements helped the sand to filter dirty water. Surprisingly, he discovered that he could remove up to 85% of the phosphorus (the nutrient that feeds algae in lakes) from a water sample, simply by chopping up steel wool and mixing it in with the sand.

Since 2005, iron-enhanced sand filters have moved from the laboratory into the field, where they are quickly becoming a popular tool in the fight against stormwater pollution. Often, the filters are built around the perimeter of stormwater ponds or filtration basins to enhance their function. Two years ago, the Comfort Lake – Forest Lake Watershed District worked with Washington County and SRF Consulting to install an iron-sand filter as part of a large stormwater treatment project north of Broadway Ave.. As it was originally designed, the sediment pond and filtration basin would have removed 32 pounds per year of phosphorus from runoff that eventually flows through Bixby Park wetlands to the Sunrise River. Adding an iron enhanced sand filter to the basin, enabled it to filter out an additional 5.4 pounds of phosphorus per year.

The Ramsey-Washington Metro Watershed District used iron-enhanced sand to improve the effectiveness of 55 raingardens it built at the Maplewood Mall as part of a massive stormwater retrofit project completed in 2012. The gardens filter 9 million gallons of polluted runoff from the mall parking lot before it flows through stormwater pipes to Kohlman Lake.

As iron-enhanced sand filters becomes more common, local water managers and engineers continue to monitor their effectiveness, making modifications when needed to ensure that they are functioning properly. Meanwhile, researchers like Andy Erickson continue to create and innovate, in search of the next great technology for keeping our water clean.

Source: Lillie News

Read More Related Content On This Topic - Click Here

Media

Taxonomy

• Sand Filter
• Environment
• Watershed
• Infrastructure
• Storm Water Management