Date of Award
Master of Science
Civil, Construction, and Environmental Engineering
Michelle L. Soupir
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 bottom sediments 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 bottom sediments: sand, sand-silt, and sand-silt overlain 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 filtration techniques. Attachment ratios increased as particle sizes decreased and percent of attached E. coli generally decreased after the critical shear stress was surpassed. Statistical analysis found that both bottom sediments and flow rate impact attachment of E. coli. The calculated unattached E. coli resuspension rates from the different bottom sediments were 1.32E-6 cfu/m2/s for sand, 1.03E-6 cfu/m2/s for sand-silt, and 1.78E-6 cfu/m2/s for biofilm. The calculated attached E. coli resuspension rates were 3.84E-6 cfu/m2/s for sand, -2.84E-6 cfu/m2/s for sand-silt, and -8.06E-6 cfu/m2/s for biofilm. Statistical analysis found that bottom sediments and flow rate impact total E. coli resuspension, attached E. coli resuspension, and unattached E. coli resuspension. The model, calibrated using the calculated resuspension values, was able to accurately represent both attached (r2= 0.91) and unattached (r2= 0.85) E. coli resuspension. This work increases knowledge and ability to track particles in different environments, by separating unattached and attached resuspension. It is possible to model attached resuspension with sediment resuspension equations. The risk of unattached fraction of E. coli resuspension still needs further assessment. These equations should be applied to data collected in the field where turbulent flow may affect the resuspension of various bottom sediments.
Amy A Cervantes
Cervantes, Amy A., "Resuspension of E. coli Under Controlled Flows and Stream Bottom Sediments" (2012). Graduate Theses and Dissertations. 12580.