Microorganisms in streams are potentially transported as freely suspended organisms or attached to particulates. Many water quality models currently neglect resuspension, an important process to predict in-stream bacteria concentrations. The objective of this work is to measure resuspension of E. coli from different substrates under a range of flows. An assessment of the attached fraction and resuspension rate was completed by measuring E. coli concentrations in a recirculating flume at two locations. The test was completed for three different substrates: sand, sand-silt, and sand-silt covered with biofilm. The experiments were conducted at flows below, and above the calculated critical shear stress, as well as two different water depths. Attachment ratios were assessed using a combination of shaking and filtering techniques. The results showed that attachment ratios increased as particle sizes decreases and cohesion increased. Attachment decreased after the critical shear stress was surpassed; sand attachment decreased from 14.29% to 11.44%, sand-silt decreased from 42.01% to 20.59% and biofilm decreased from 82.52% to 11.77% (values averaged for two collection points). The resuspension calculations show resuspension of attached particles at the first test point (8.54E-7 to 1.74E-5 CFU/m~2/s) and deposition at the second test point (-2.99E-5 to 1.69E-5 CFU/m~2/s). At the first sample location there was a steady increase of resuspension as shear stress increased whereas at the second sample location the resuspension rate remained nearly constant.
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