Bacterial Plume Dynamics in the Marshland Upwelling System Employed in the Near Freshwater Conditions
The marshland upwelling system (MUS) was installed in a floatation marsh along the banks of the Bayou Segnette Waterway, Louisiana. This site was characterized by native groundwater of low salinity regime. Previous studies focused on the removal of fecal pathogens from settled/raw and secondarily treated wastewater under high saline groundwater conditions. The objectives of this research were to: 1) quantify the impact of natural die-off on bacterial removal within the MUS, 2) determine bacterial retardation rates in laboratory-repacked sandy loam soil columns, and 3) evaluate the effectiveness of the MUS in removing fecal pathogens from settled, raw wastewater. Varying salinities and temperatures were used to investigate the inactivation rates for fecal coliforms. Rapid inactivation was recorded for each temperature studied, followed by a much slower die-off process. The higher temperature (25°C) was more detrimental to fecal coliform survival than the 20°C study. Increasing salinity concentrations was not detrimental to fecal coliform survival. Continuous injection experiments performed in one-dimensional columns packed with sandy loam soils from the field recorded bacterial retardation factors of between 4.7 and 7.7 with respect to the conservative wastewater tracer. Higher limitations to bacterial transport are expected under field-scale conditions. The MUS was evaluated under three separate injection schemes: a high flow/low temperature loading (HFLT), a 0.95 L/min and a 1.9L/min studies injecting for 15 minutes every hour. The 0.95 L/min flowrate was most suited for bacterial removal. The injection depth employed impacted fecal coliform removal rates. Mean influent concentrations of 92,510±489,614 MPN/100mL were reduced to effluent concentrations of 4.0±7.6 MPN/100mL (observed in the 2.7 m wells). Four-log reductions in influent concentrations were observed within a one-meter radial distance from the injection point. Overall removal followed a first-order decay relationship with respect to vector distance. Removal rate constants for fecal coliforms ranged from 2.0 -4.0 m-1, and that for E. coli ranged from 1.7-4.0 m-1.
Advisor:John Pardue; Ron F. Malone; Kelly A. Rusch
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Keywords:civil environmental engineering
Date of Publication:10/04/2004