Vegetative filter strips (VFS) are commonly used best management practices for removing contaminants from runoff. Additional research is warranted to determine their efficiency and the most appropriate metrics for predicting fecal bacteria reductions. The objective of this research was to determine VFS effectiveness in removing Escherichia coli from runoffrelative to inflow rate, infiltration capacity, and flow concentration. This research also investigated the presence of E. coli in runofffrom clean water runon after diluted manure runon events. A laboratory-scale VFS soil box (200 cm long, 100 cm wide, 7.5% slope) was packed with a sandy loam soil. Ten constant-flow VFS experiments were conducted with and without vegetation (8-10 cm ryegrass [Lolium perenne L.]) at low (20-40 cm3 s-1), medium (40-60 cm3 s-1), and high (85-120 cm3s-1) flow rates and for a full (100 cm) or concentrated (40 cm) VFS flow width to simulate a channelizing flow condition. Two runon events were investigated for each experimental condition: (i) diluted liquid swine manure runon and (ii) clean water runon 48 h afterward. Escherichia coli was used as an indicator of fecal contamination and was quantified by the most probable number (MPN) technique. No E. coli concentration reductions were observed based on peak outflow concentrations, and only small concentration reductions were observed based on outflow event mean concentrations. The E. coli mass reductions ranged from 22 to 71% and were strongly correlated to infiltration or runoffreduction (R2 = 0.88), which was dependent on the degree of flow concentration. Little to no effect of sedimentation on E. coli transport was observed, hypothesized to be due to minimum E. coli attachment to sediment particles because the bacteria originated from manure sources. Th erefore, the design of VFS for bacteria removal should be based on the infiltration capacity in the VFS and should prevent concentrated flow, which limits total infiltration. The E. coli event mean concentrations in clean water runon experiments were between 10 and 100 MPN per 100 mL; therefore, under these conditions, VFS served as a source of residual E. coli from previous runon events.
ASJC Scopus subject areas
- Environmental Engineering
- Water Science and Technology
- Waste Management and Disposal
- Management, Monitoring, Policy and Law