Modeling the effects of exogenous bacteria in bioaugmentations on the fate and transport of subsurface organic contaminants

This dissertation develops three mathematical models that represent one-dimensional contaminant transport in the presence of colloids in dual-porosity soils, two-dimensional contaminant bioaugmentation in single-porosity soils, and two-dimensional contaminant bioaugmentation in dual-porosity soils. Bioaugmentation is considered as a technique for improving inherent biodegradation processes by injecting exogenous bacteria and nutrients. The effects of the injection of bacteria and of their migration during the operation of bioaugmentation on the contaminant biodegradation processes are investigated by applying both single- and dual-porosity models to case studies. A biomodal approach is adopted to investigate the effects of the hydrogeologically ineffective region in dual-porosity soils on the contaminant transport and biodegradation. Biodegradation by bacteria in both the solid and aqueous phases is incorporated into the models, and the microcolony concept is used to represent solid phase bacteria. The models also consider permeability reduction caused by biomass accumulation.; Having proposed mathematical models to represent the fate and transport of a subsurface organic contaminant during in situ bioaugmentations, this dissertation conducts numerical experiments by applying the models to case studies. Simulation results demonstrate that the proposed models can successfully represent the fate and transport of the subsurface organic contaminant in the presence of colloids or bacteria in single- and dual-porosity soils. The presence of the immobile region in dual-porosity soils is observed to serve as a solute reservoir and to further enhance the contaminant transport in the presence of colloids. The immobile region also serves to reduce the bioavailability of contaminants and the efficiency of biodegradation processes by keeping contaminants from being utilized by bacterial metabolism. Model results indicate that, in operations of bioaugmentation, the injection of exogenous bacteria and nutrients required to accelerate bacterial metabolism clearly improves the performances of the contaminant transport. The success of in situ bioaugmentation involving the injection of bacteria and nutrients depends on controlling the contact of biodegrading microorganisms with target contaminants and supplying enough nutrients and electron acceptors to stimulate microbial activities into a contaminated zone.