The project addresses a common challenge in the remediation of groundwater contaminated with chlorinated volatile organic compounds (CVOCs) and 1,4-dioxane. CVOCs include chlorinated solvents, such as trichloroethylene (TCE) and 1,1,1-trichloroethane (1,1,1-TCA), and their degradation products. Many CVOCs and 1,4-dioxane are known or potential human carcinogens and on the Substance Priority List (SPL) for Superfund sites. CVOCs bioremediation under anaerobic conditions (i.e. reductive dechlorination) is well established. However, bioremediation of mixtures of CVOCs and 1,4-dioxane is not yet feasible due to at least the following three obstacles: 1) low biodegradability of 1,4-dioxane at environmentally relevant concentrations, 2) requirement for aerobic conditions for 1,4-dioxane metabolism but anaerobic conditions for most CVOCs metabolism, and 3) inhibition of 1,4-dioxane biodegradation by CVOCs. This project proposes the following combined remediation approach to address these challenges: first, an innovative macrocyclic material approach to selectively adsorb CVOCs and promote the growth of dechlorinating biofilm on the material surface to anaerobically biodegrade CVOCs. After the CVOCs treatment, another type of innovative macrocyclic material as an effective and selective sorbent for 1,4-dioxane sustains biofilms consisting of a highly efficient culture to aerobically metabolize 1,4-dioxane. The macrocyclic molecules, which comprise repeating cyclic oligomers with unique geometry and internal chemistry, form specific host-guest complexes with only selected guest molecules (i.e., 1,4-dioxane or CVOCs). A highly efficient 1,4-dioxane-metabolizing culture (previously established) is much more effective at low, environmentally relevant concentrations compared to all others reported in literature. To understand the mechanisms of how the novel sorbents enhance bioremediation and to demonstrate the feasibility of the proposed remediation approach, the researchers will conduct the following work: 1) Computational study, synthesis, and characterization of novel macrocyclic materials. Two sorbents, one that selectively and reversibly adsorbs CVOCs and another that selectively adsorbs 1,4-dioxane will be optimized for use in the bioremediation studies. 2) Mechanistic study of the highly efficient 1,4-dioxane-metabolizing culture. Key microorganisms responsible for the high affinity to 1,4-dioxane in the mixed culture will be isolated and investigated for their degradation intermediates, pathways, and kinetics. 3) Elucidation of interactions among contaminants, microbial cultures, and the novel sorbents. To achieve this, completely mixed flow experiments will be performed, and they will be coupled with mathematical modeling that incorporates phenomena of both sorption and biodegradation in biofilms. 4) Proof-of-concept column studies for bioremediation of CVOCs and 1,4-dioxane mixtures. Two long-term column studies will be performed: ex situ treatment of 1,4-dioxane and in situ bioremediation of CVOCs and 1,4-dioxane mixture in series. Performance objectives will be Maximum Contaminant Levels for CVOCs and the Health Advisory Level for 1,4-dioxane (0.35 g/L).
Both chlorinated volatile organic compounds (CVOCs) and 1,4-dioxane are potential or known human carcinogens. 1,4-dioxane, an emerging contaminant above the health-based reference level in 6.9% of the U.S. public water supplies, is commonly found to co-occur with CVOCs in contaminated groundwater including Superfund sites. This project aims at enhancing the remediation of 1,4-dioxane or its mixture with CVOCs by combining novel macrocyclic materials for contaminant adsorption with bioremediation, and investigates the interactions among the adsorbents, microbes, and contaminants.
