Project overview
Standard stormwater filters use sand to retain solids and, with them, some particulate phosphorus, helping to prevent sediment pollution from entering waterbodies. However, standard sand filters do not retain dissolved phosphorus, which makes up approximately 44% of the total phosphorus load in stormwater. Thus, in order to meaningfully reduce phosphorus pollution, stormwater managers need to retain dissolved phosphorus. To accomplish this, many stormwater managers in Minnesota use iron-enhanced sand filters (IESFs). IESFs incorporate iron filings into the sand filter media. The iron oxidizes, becomes positively charged, and adsorbs phosphate ions. An iron-enhanced filter can retain 80% or more of the phosphorus that is dissolved in stormwater.
However, there are disadvantages to using iron filings for phosphorus retention. Iron filings can clump together, reducing the permeability of the filter. Also, when the iron can no longer adsorb any more phosphate ions, it needs to be replaced, but the cost of the filings makes replacing spent media prohibitively expensive for many IESF owners. Identifying a less expensive, longer-lasting alternative to iron filings would greatly reduce the cost of removing phosphorus from stormwater.
Research questions
- Which alternative enhancing agent(s) could be a cost-effective replacement for iron filings in sand filters that are designed for stormwater phosphorus retention, without decreasing filter performance?
- What are optimal design specifications for stormwater sand filters with alternative enhancing agent(s)?
- How do you determine if an enhancing agent is spent?
- What is the cost, cost-effectiveness, and anticipated life-span of alternative enhancing agent(s) in stormwater sand filters?
Key innovations/contributions
This project will identify a sand filter media material that can remove dissolved phosphorus from stormwater runoff more cheaply than iron.
What does this mean for Minnesota?
The results of this study will enable stormwater managers throughout the State of Minnesota to more cost-effectively reduce dissolved phosphorus loads in stormwater runoff and better meet stormwater management goals. Reducing the cost of phosphorus retention would free up valuable resources, while reducing phosphate release into our lakes and rivers. Less phosphorus in our water will result in better water quality, healthier aquatic habitats, and improved recreational opportunities for Minnesota residents.