Watershed Achievements Report

Statewide Watershed Achievements Report 2015
Enhanced filter media for removal of
dissolved heavy metals and phosphorus
from stormwater runoff
The purpose of this project was to research materials
that could be used in new or renovated sand filters,
infiltration systems, rain gardens, and buffer strips to
capture significant amounts of dissolved heavy metals,
phosphorus, and nitrogen that are typically found in
urban and agricultural runoff. Literature was thoroughly
reviewed to document performance by existing
stormwater treatment practices and investigate potential
enhancements for water quantity reduction and capture
of dissolved heavy metals, phosphorus, and nitrogen.
Batch studies found that several enhancing agents such
as commercial products and organic materials captured
a substantial amount of dissolved metals; iron-based
products captured a significant fraction of dissolved
phosphorus; and two activated carbons were found to
remove a significant fraction of nitrate from synthetic
stormwater.
Column studies confirmed that activated carbons
removed dissolved nitrate in an upflow system with 15
minutes of contact time, but nitrate ions competed for
sorption sites with other ions (e.g., carbonate). Field
verification experiments were designed to determine
how the treatment technology could be expected to
perform in field applications. The activated carbons
performed better under simulated field conditions
than laboratory conditions, despite significantly shorter
contact time. In addition, nitrate competition with
other ions was not observed in the field verification
experiments. The Thomas model can be used to estimate
and represent removal of nitrate from stormwater by
activated carbon.
A filter containing an activated carbon from this study
that is 5% of the contributing watershed area will have an
estimated lifespan of between 40 and 100 storm events
(rainfall depth of 5 cm (2 inch), nitrate concentration
of 0.6 mg NO3-N/L). Additional research is needed to
determine if this is cost-effective, or if captured nitrate
can be denitrified between storm events to increase
capacity and extend the lifespan of activated carbon
filters for nitrate removal.
Goals
• Determine performance capabilities of existing
stormwater treatment practices
• Identify and evaluate potential enhancements to
existing stormwater treatment practices that remove
dissolved metals, phosphorus, and nitrogen
• Establish design criteria for enhanced media filters
Results that count
• The Literature Review provides details on
performance of existing practices.
• The experiments identified and evaluated various
enhancements for removing dissolved metals,
phosphorus and nitrogen.
• The recommendations provide design criteria
necessary for sizing and estimating the performance
of an enhanced media filter.
Financial information
Funding type: Section 319
Grant amount: $404,000
Final in-kind: $330,546
Contact information
Kevin McKoskey
University of Minnesota
450 McNamara Alumni Center, 200 Oak Street
Minneapolis, MN 55455
612-624-5066
MPCA Project Manager: Greg Johnson
The picture above shows the column experiment system used
in the study to examine the performance of the treatment
technology using real stormwater. This picture was taken at the
St. Anthony Falls Laboratory at the University of Minnesota.
Minnesota Pollution Control Agency www.pca.state.mn.us 30