Biodegradation of cyclic and alkyl ethers in subsurface and engineered environments

The presence of ethers in the environment presents a serious threat to human and ecological health. Ethers are generally soluble and resistant to biodegradation. As a result, they are highly mobile once released to the environment. The objective of this research was to study the biodegradability of several ethers under conditions representative of both contaminated aquifers and engineered reactors.; In the first phase of this study, the biodegradability of two cyclic ethers, 1,4-dioxane and tetrahydrofuran (THF) was studied in contaminated aquifer sediment. 1,4-Dioxane is a miscible ether that is highly resistant to microbial oxidation and is a groundwater contaminant in North Carolina. 1,4-Dioxane and THF were incubated in soil microcosms containing native groundwater and sediment from several aquifers contaminated with 1,4-dioxane. No biodegradation of either 1,4-dioxane or THF was observed under conditions representative of the contaminated aquifer after one year of incubation. However, biodegradation of both ethers occurred in microcosms from one site incubated at 35°C and containing both 1,4-dioxane and THF.; This biodegradation activity was further explored under batch conditions. It was determined that the biodegradation of 1,4-dioxane was strictly dependent on the presence of THF. 1,4-Dioxane biodegradation repeatedly ceased when THF was depleted from solution. An experiment using 14C-labelled 1,4-dioxane was also performed to determine its fate during biodegradation. The majority of the 14C-1,4-dioxane (78.1%) was mineralized to 14CO2 while a small fraction (2.1%) was incorporated into particulates. The consortium was also capable of biodegrading the ethers 1,3-dioxane, methyl t-butyl ether (MTBE), ethyl t-butyl ether (ETBE), t-amyl methyl ether (TAME), and diisopropyl ether (DIPE), all in the presence of THF. The biodegradation of these ethers was determined to be occurring via a cometabolic process.; A kinetic model was then used to evaluate the biodegradation of 1,4-dioxane and THF. Various kinetic parameters were determined and the model was fit to batch data representing various initial THF/1,4-dioxane ratios.; Finally, the ability of this consortium to be utilized in attached growth reactors was investigated. A laboratory-scale trickling filter and a rotating biological contactor (RBC) were constructed to treat water containing low concentrations of 1,4-dioxane, THF or MTBE. Both reactors were capable of removing at least 90--95% of the influent ethers under certain loading conditions. A tanks-in-series model coupled with the cometabolic model was employed to predict the effluent 1,4-dioxane and THF concentrations from the trickling filter. The model was effective at predicting THF biodegradation, yet over predicted the amount of 1,4-dioxane degraded.