Pond treatment with spent lime to control phosphorus release from sediments

Sedimentation ponds that accumulate particles and phosphorus in stormwater runoff are a standard and widely applied stormwater best management practice. However, just as internal loading occurs in lakes during warm summer periods when the potential for oxygen depletion is greatest, aging ponds have the potential to release more phosphorus than is captured during summer months. Dredging is a potential, but expensive, option to improve pond performance, but phosphorus release may occur long before a pond is filled with sediment. Areal applications of alum and iron can control phosphorus release, but incur raw material production costs.

In cooperation with RWMWD, VLAWMO and City of White Bear Lake staff, Barr Engineering completed a study to evaluate the application of spent lime (amorphous calcium carbonate from drinking water treatment) to pond sediments to reduce phosphorus release. Spent lime can reduce phosphorus release by forming calcium phosphate and potentially by increasing the pH of the treated sediments to facilitate iron and aluminum phosphate binding. This study included laboratory and field components intended to validate the efficacy of large-scale applications. The laboratory component included the addition of spent lime at a range of doses to phosphorus rich pond sediment to determine optimal spent lime dosing. The field component involved the addition of spent lime to two ponds, monitoring to assess sediment phosphorus release and compliance with permit conditions, and evaluations of effective methods for real application to quantify the cost-benefit of this water treatment byproduct.

This presentation will feature our conclusions of this project funded by the Minnesota Stormwater Research Council.