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TECHNICAL REPORTS

Surface Water Quality

Managing Biosolids Runoff Phosphorus Using Buffer Strips Enhanced with Drinking Water Treatment Residuals

Agricultural and Biological Engineering Dep., Pennsylvania State Univ., University Park, PA 16802

^* Corresponding author (hae1{at}psu.edu).

Received for publication June 25, 2007. Vegetated buffers strips typically have limited ability to reduce delivery of dissolved phosphorus (DP) from agricultural fields to surface waters. A field study was conducted to evaluate the ability of buffer strips enhanced with drinking water treatment residuals (WTRs) to control runoff P losses from surface-applied biosolids characterized by high water-extractable P (4 g kg^–1). Simulated rainfall (62.4 mm h^–1) was applied to grassed plots (3 m x 10.7 m including a 2.67 m downslope buffer) surface-amended with biosolids at 102 kg P ha^–1 until 30 min of runoff was collected. With buffer strips top-dressed with WTR (20 Mg ha^–1), runoff total P (TP = 2.5 mg L^–1) and total DP (TDP = 1.9 mg L^–1) were not statistically lower ( = 0.05) compared to plots with unamended grass buffers (TP = 2.7 mg L^–1; TDP = 2.6 mg L^–1). Although the applied WTR had excess capacity (Langmuir P maxima of 25 g P kg^–1) to sorb all runoff P, kinetic experiments suggest that sheet flow travel time across the buffers (30 s) was insufficient for significant P reduction. Effective interception of dissolved P in runoff water by WTR-enhanced buffer strips requires rapid P sorption kinetics and hydrologic flow behavior ensuring sufficient runoff residence time and WTR contact in the buffer. Substantial phosphate-adsorbent contact opportunity may be more easily achieved by incorporating WTRs into P-enriched soils or blending WTRs with applied P sources.

Abbreviations: BMP, best management practice • BPR, biological phosphorus removal • DP, dissolved phosphorus • PP, particulate phosphorus • PSC, phosphorus source coefficient • PSI, phosphorus saturation index • RDP, runoff dissolved phosphorus • TDP, total dissolved phosphorus • TP, total phosphorus • WEP, water-extractable phosphorus • WTR, water treatment residual