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<br /> New treatment practice removes dissolved phosphate from stormwater
<br /> Stormwater treatment practices have long focused To work effectively, the
<br /> on removing suspended solids and particles from system needs to stay oxy-
<br /> stormwater runoff(including the SAFL Baffle—see genated to ensure the
<br /> article below). However, as much as 40% to 50% of iron oxides remain aerobic,
<br /> the pollutants in stormwater are actually dissolved Erickson said. Filings should be
<br /> ell
<br /> co pre-
<br /> mpounds, including nutrients such as phospho- 8% or less iron by weight t
<br /> �A il
<br /> rus. These pollutants are not settled or filtered in vent clogging.
<br /> many existing stormwater runoff treatment systems Not all sites are candidates for
<br /> found across the region, state, and nation. a Minnesota Filter. Pollutants S'.
<br /> Researchers at the U of M's St. Anthony Falls carried by stormwater can vary
<br /> Laboratory(SAFL)—led by research scientist greatly with different locations,
<br /> Andrew Erickson and professors Peter Weiss and storms,time of year, and pollut-
<br /> fohn Gulliver—have identified techniques to remove ant sources,Erickson explained. The Minnesota Filter can be used in many applications,such as this site in Maplewood.
<br /> the dissolved compound phosphate from storm- Most urban watersheds need to
<br /> water,with excellent results. Their iron-enhanced treat both solids and dissolved
<br /> sand filtration system,named the Minnesota Filter, compounds. maintenance requirements are still being deter-
<br /> has been installed in a number of locations around The cost of the system depends on the size and mined. Lab modeling indicates the system will
<br /> the Minneapolis-St. Paul metro region. Erickson type of the installation. In one example, a quarter- last more than 35 years before the iron runs out of
<br /> provided design and performance highlights of their acre site,material and labor costs increased by capacity,which is longer than the design life of most
<br /> work,which is funded by the Minnesota Local Road about 15% (for mixing the sand and iron). For other filter systems.The next several years of monitoring
<br /> Research Board, at the CTS research conference in applications,more efficient approaches could get the will provide data about maintenance cycles and dis-
<br /> May. additional cost down to perhaps 5% or 10%. "We're posal issues,he said.
<br /> The Minnesota Filter is a new technique in which improving that all the time with how we spec it," Sign up for SAFUs stormwater assessment and
<br /> iron filings are added to a sand filtration system. Erickson said. 'And even though it costs more, other maintenance newsletter, UPDATES, at
<br /> When exposed to rainfall,the iron forms iron practices are not touching that dissolved fraction." littl)://storniwzitei-.saft.Liii-iii.edLi. VAP,
<br /> oxides (rust),which adsorb phosphate. The system Since the installations are relatively new, —Pamela Snopl, LTAP editor
<br /> can be used in many applications including surface
<br /> sand filters,wet detention basins,permeable weirs, Success in the field
<br /> ditch check blocks, and rain gardens,Erickson said.
<br /> The system was first installed in Maplewood in The Minnesota Filter has "worked extrbmelywell,"-says Cliff Aichinger, district administrator for Ramsey
<br /> 2009 using 5% iron filings by weight.A number Washington Metro Watershed Distri ct.Aichinger was a member of the technicakadvisory panel for the'original
<br /> of similar systems have been installed,= uch as a -project that developed this technology, and his district did the first field installation.
<br /> field test in Prior Lake that used 7% iron filings "We have adopted it as a practice virtually every:chance,we get," Aichinger says. 'We think it's a.1very useful
<br /> in trenches for wet detention ponds. Results from technique."
<br /> que."The biggest stormwater management problem in his-district is dissolved phosphorous, he says, and the
<br /> monitoring initial installations show an average of filter is ."one of th I e few techniques out there that is targeting it." He adds that the technique is "a good practice
<br /> 70%phosphate reduction in stormwater. for small sites, so it's appropriate in Urban areas as well.And the cost is minimal:" rymp
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