Watershed Achievements Report
wq-cwp8-18
wq-cwp8-18
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Minnesota Upper Mississippi River Basin River Basin <strong>Watershed</strong> <strong>Achievements</strong> <strong>Report</strong> 2008 2015<br />
Twin Cities <strong>Watershed</strong><br />
Permeable Reactive Barrier for<br />
Phosphorus Removal<br />
The goal of this project was to determine the<br />
effectiveness of using “spent lime”, created by local water<br />
utilities during drinking water clarification, to reduce<br />
phosphorus in storm water flow. Spent lime contains<br />
calcium, iron, and/or aluminum, all three of which bind<br />
P. Because of the potential for high phosphorus binding<br />
capacity, we hypothesize that spent lime could be used<br />
in a reactive barrier system to remove phosphorus from<br />
storm water runoff in a cost effective manner. Laboratory<br />
experiments were conducted to determine the optimum<br />
conditions needed for effective phosphorus removal and<br />
in what type of storm water a spent lime barrier would<br />
be most effective. The results of these experiments were<br />
the basis for the pilot study to determine the P removal<br />
effectiveness under field conditions.<br />
To effectively and permanently remove phosphorus,<br />
phosphate must be incorporated into recalcitrant<br />
organic material or be bound to cations such as<br />
calcium, magnesium, or unreducible trace metals<br />
such as aluminum. Spent lime is an abundant waste<br />
byproduct of drinking water treatment and the primary<br />
component of spent lime is calcium carbonate.<br />
Fortunately, calcium chemically prefers to be bound<br />
to phosphate over carbonate, and phosphate is readily<br />
converted into calcium phosphate in the presence<br />
of high concentrations of calcium carbonate (Stumm<br />
and Morgan, 1996). Spent lime has an advantage over<br />
limestone in that it consists of recently precipitated and<br />
hence more available calcium carbonate. The use of<br />
spent lime for stormwater treatment is a new concept.<br />
A treatment cell with spent lime is not precipitating or<br />
flocculating phosphate (e.g., like alum), and it is not<br />
necessarily intended to filter as do sand filters. Rather, it<br />
is a chemical “substitution” reaction whereby the newly<br />
formed calcium phosphate simply resides in the cell<br />
where the calcium carbonate once resided.<br />
Goals<br />
• Quantify the percentage improvement in phosphorus<br />
removal that can be achieved with the addition of<br />
spent lime to storm water compared to storm water<br />
treated by traditional sedimentation practices.<br />
Installation of the spent lime test cell on the NW corner of<br />
Larpenteur Avenue and Prosperity Road in Maplewood,<br />
Minnesota.<br />
• 30 to 70% P removal improvement.<br />
• Determine if this practice is warranted for a full scale<br />
installation for stormwater treatment.<br />
Results that count<br />
• Monitoring was effectively completed to allow for an<br />
accurate analysis of the treatment results and cost<br />
effectiveness of the BMP.<br />
• The demonstration treatment cell removed an average<br />
of 63.6% total phosphorus and 63.9% of total dissolved<br />
phosphorus.<br />
• Our analysis and testing has confirmed that this is a<br />
practical and cost effective BMP for the reduction of<br />
total and dissolved phosphorus in urban settings.<br />
Financial information<br />
Funding type: Section 319<br />
Grant amount: $89,200<br />
In-kind: $0<br />
Matching funds: $82,222.51<br />
Contact information<br />
Cliff Aichinger, Administrator<br />
Ramsey-Washington Metro <strong>Watershed</strong> District<br />
2665 Noel Drive<br />
Little Canada, MN 55117<br />
651-792-7957<br />
cliff@rwmwd.org<br />
MPCA Project Manager: Brooke Asleson<br />
Minnesota Pollution Control Agency www.pca.state.mn.us 110