Cleaning Stormwater Through Iron Filtration

Phosphorus pollution is the primary cause of algae blooms in lakes.  In addition to being unsightly, severe algae growth can deplete the oxygen levels in the lake and seriously affect fish health.  In severe cases, extreme algae growth can give rise to the toxic bluegreen algae that has been known to kill pets that drink the tainted water.

The storm water runoff that enters catch basins and storm sewer pipes has been shown to carry phosphorous laden sediment as well as soluble phosphorus.  The recent construction through the Storm Lake Golf Course includes storm water ponds that are designed to capture and effectively remove the sediment borne phosphorous.  However, research shows that dissolved phosphorous constitutes approximately 45% of the total load carried by storm water runoff.  Therefore, innovative stormwater treatment practices are necessary to fully protect Storm Lake from significant, and costly, water quality problems for future generations.   

A relatively recent advancement in the removal of dissolved phosphorus from urban stormwater is Iron Enhanced Sand Filtration.  While applications of the iron filter continue to progress with continued popularity, they are typically used in overflow areas of traditional stormwater ponds.  As stormwater flows into the pond, the water surface rises into the iron filter area and trickles down through the sand.  The filtration medium contains approximately 5% iron filings by weight and is mixed into the sand medium prior to placement in the filtration area.  In between rainfall events, the iron will rust which creates an ideal condition for phosphorus to absorb.  The iron continues to break down and rust over time, creating new sites for phosphorus absorption.  The East Area Water Quality project includes an iron enhanced filtration “bench”, integrated into a sand trap area, in one of the golf course ponds that filters stormwater runoff from much of the east side of Storm Lake.  Construction of this "bench" has been completed and the iron filings will be incorporated into the bench in the upcoming week.