Doctor of Philosophy (PhD)
Civil and Environmental Engineering
The objective of this dissertation was to investigate the fate and transport of microorganisms in coastal subsurface. Two topics were studied: (1) evaluation of the performance of the Marshland Upwelling System (MUS) in removing fecal bacteria and the background recovery after it is shut down; (2) Investigation of the effects of salinity and soluble organic matter (SOM) on sorption of MS-2 and development of a model to describe the sorption and transport process. The MUS showed effective performance in removing fecal bacteria during its 32 month operation period at Bayou Segnette Site. The removal efficiency was increased with its operation as the results of deposition of solid particles from primary wastewater and the growth of biofilms in subsurface. After the MUS shutdown, the subsurface environment recovered completely from the fecal bacteria loading in less than 4 months due to fast fecal bacteria natural die-off. Laboratory experiments were conducted to examine the effects of salinity and SOM on MS-2 sorption in one-dimensional sand and sandy soil columns. A two-site reversible-irreversible sorption model was found to describe MS-2 sorption successfully. In sand column tests, salinity increased MS-2 attachment by compressing double layers on reversible sorption sites and changing reversible sorption sites into irreversible sorption sites by reversing charges on the surface of some sand particles. SOM inhibited MS-2 sorption by expanding the double layer thickness on reversible sites and competing with MS-2 for the same binding place on irreversible sites. In sandy soil column tests, the bonded and dissolved soil organic matters suppressed the salinity and SOM effects and significantly reduced MS-2 adsorption. The bonded soil organic matter reduced sorption sites by occupying a great portion of sorption sites, and the dissolved soil organic matter expanded the double layer thickness on reversible sorption sites and competed with MS-2 for the same binding place. A fate and transport model, coupled with two-site reversible-irreversible sorption process, was developed to describe MS-2 sorption and transport in sand and sandy soil columns. The fate and transport model fitted the experimental data well with corresponding model parameters, which were identified using the BFGS method and sensitivity-equation method.
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Cao, Haibo, "Fate and Transport of Microorganisms in Coastal Subsurface-Experiment and Modeling" (2008). LSU Doctoral Dissertations. 3812.