Managing biosolids runoff phosphorus using buffer strips enhanced with drinking water treatment residuals

Area of Science:

• Environmental Science
• Soil Science
• Water Quality Management

Background:

• Vegetated buffer strips have limited effectiveness in reducing dissolved phosphorus (DP) delivery to surface waters from agricultural sources.
• Biosolids application to agricultural fields can lead to significant phosphorus (P) runoff due to high water-extractable P content.
• Drinking water treatment residuals (WTRs) are a potential amendment for improving P sorption in buffer systems.

Purpose of the Study:

• To evaluate the efficacy of buffer strips enhanced with drinking water treatment residuals (WTRs) in mitigating phosphorus runoff from surface-applied biosolids.
• To determine if WTR application to vegetated buffers can reduce total phosphorus (TP) and dissolved phosphorus (DP) losses in runoff.
• To investigate the influence of runoff residence time and WTR-biosolid interaction on phosphorus removal.

Main Methods:

• A field study using simulated rainfall (62.4 mm h(-1)) on grassed plots with and without WTR-amended buffer strips.
• Surface application of biosolids (102 kg P ha(-1)) followed by collection of runoff for 30 minutes.
• Analysis of total phosphorus (TP) and total dissolved phosphorus (TDP) concentrations in runoff.
• Assessment of WTR P sorption capacity (Langmuir P maxima) and kinetic experiments.

Main Results:

• WTR-enhanced buffer strips (20 Mg ha(-1)) did not significantly reduce TP (2.5 mg L(-1)) or TDP (1.9 mg L(-1)) in runoff compared to unamended buffers (TP = 2.7 mg L(-1); TDP = 2.6 mg L(-1)).
• Despite WTRs having a high P sorption capacity (25 g P kg(-1)), the short runoff residence time (approx. 30 s) across the buffer limited P reduction.
• The applied WTR was theoretically capable of sorbing all the P in the runoff, indicating kinetics and contact time were limiting factors.

Conclusions:

• Top-dressing WTRs onto buffer strips is insufficient to significantly reduce phosphorus runoff when runoff residence time is limited.
• Effective dissolved phosphorus interception by WTR-enhanced buffers requires rapid P sorption kinetics and sufficient contact time between WTR and runoff.
• Incorporating WTRs into P-enriched soils or blending them with P sources may enhance phosphate-adsorbent contact and improve P retention.