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Of Biofilms and Treatment Trains: Removing 1,4-Dioxane and Co-contaminant Mixtures from Water


Addressing trace organic contaminants (TrOCs) in freshwater supplies is increasingly important to ensure continued water security as it becomes stressed by rising demand and climate change. While many physical-chemical technologies are ineffective or cost-prohibitive for removing these contaminants from water, biological treatment is becoming an appealing strategy due to generally lower energy and chemical requirements, resulting in improved sustainability and cost-effectiveness. The research presented in this dissertation describes the treatment of environmentally relevant mixtures of water contaminants using biodegradation by bacterial biofilms and treatment trains. 1,4-Dioxane, an industrial solvent and solvent stabilizer, which is a probable carcinogen frequently detected in water supplies, was used as a model TrOC. First, a propanotroph, Mycobacterium austroafricanum JOB5, grown planktonically or in biofilms, was demonstrated to cometabolically biotransform 1,4-dioxane in the presence of carcinogenic hexavalent chromium [Cr(VI)]. In both growth modes, extracellular polymeric substances shielded the cells and mitigated inhibitory effects of Cr(VI) at levels as high as 10 mg/L. Next, Pseudonocardia dioxanivorans CB1190 biofilms grown on ZSM-5 zeolite (bio-zeolite) were capable of sustaining their growth by biodegrading 1,4-dioxane in aqueous mixtures containing chlorinated volatile organic compounds (CVOCs). Isotherm modeling and molecular dynamics simulations helped characterize the adsorption mechanisms of 1,4-dioxane and how CVOCs affected the overall treatment performance of the system. Bio-zeolite was able to degrade 1,4-dioxane in the presence of trichloroethene or cis-1,2-dichloroethene with little observable inhibition, but was inhibited by the presence of 5 mg/L 1,1-dichloroethene. Lastly, flow-through columns packed with granular activated carbon (GAC) bioaugmented with CB1190 biofilms (bio-GAC) were determined to remove 1,4-dioxane and CVOCs from water more effectively than abiotic GAC. Column reactors containing a bio-GAC/sand mixed bed removed 1,4-dioxane better than a stratified bed. Longer hydraulic residence times caused increased oxygen limitation due to oxygen adsorption by GAC. Additionally, appropriate application of nutrients was found to be crucial to bioreactor performance due to the presence of other microbes and possible adsorption by GAC. This research will be valuable for further developing more sustainable technologies to treat TrOC mixtures containing mixed-polarity compounds and present new directions for applying biological-physical treatment trains to address recalcitrant environmental contaminants.

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