Escherichia coli load reduction from runoff by vegetative filter strips: a laboratory-scale study

Area of Science:

• Environmental Science
• Water Quality Management
• Agricultural Engineering

Background:

• Vegetative filter strips (VFS) are established best management practices for mitigating runoff contaminants.
• Further research is needed to optimize VFS for fecal bacteria reduction and identify key performance metrics.

Purpose of the Study:

• To evaluate VFS effectiveness in reducing fecal bacteria in runoff.
• To determine the influence of inflow rate, infiltration capacity, and flow concentration on VFS performance.
• To investigate residual fecal bacteria presence in runoff following clean water application after manure events.

Main Methods:

• Laboratory-scale VFS soil boxes with and without ryegrass were subjected to controlled flow rates and widths.
• Experiments simulated diluted swine manure runon followed by clean water runon 48 hours later.
• Fecal bacteria (indicator organism) concentrations were quantified using the most probable number (MPN) technique.

Main Results:

• No significant reduction in peak outflow concentrations of fecal bacteria was observed.
• Small reductions in event mean concentrations were noted, with mass reductions (22–71%) strongly correlating with infiltration.
• Sedimentation had minimal impact; VFS acted as a residual bacteria source during clean water runon.

Conclusions:

• VFS bacteria removal efficiency is primarily governed by infiltration capacity, not flow rate or vegetation alone.
• Preventing concentrated flow is crucial for maximizing infiltration and thus bacteria removal in VFS.
• VFS design should prioritize infiltration enhancement and flow dissipation to improve fecal bacteria management.