Achieving Phosphorus Reductions From Stormwater On A Large Scale Using Coagulant Treatment

The City of Madison, Wisconsin is a Phase I stormwater permitted municipality. The MS4 permit now includes a numeric target for annual total phosphorus load reductions from stormwater based on the Rock River TMDL (WDNR, 2011). On a city-wide basis, the targeted total phosphorus (TP) reduction is approximately 50% from current conditions. The addition TP reductions will require technology beyond tradition stormwater management measures.The city is conducting a feasibility study to assess if coagulant treatment of stormwater to achieve higher total phosphorus reduction is practical and economically viable. Coagulant treatment of wastewater has been in use for many decades, and the use of coagulants for stormwater treatment has also been applied in the southeastern US (Herr, 2009), however use of this technology in northern climates is relatively untested. Initial testing of several coagulants on a local stream indicates that high levels of TP reduction (80% - 90%) may be possible.