The emerging chemical of concern 1,4-dioxane often occurs in groundwater at Department of Defense (DoD) sites in the presence of lower concentrations of chlorinated volatile organic compounds (cVOC). Historically at such sites, these cVOCs, which include 1,1-dichloroethane, cis-1,2- dichloroethene, and vinyl chloride, among others, are treated via air stripping, followed by carbon or advanced oxidation processes such as ultraviolet light-hydrogen peroxide or ozone-hydrogen peroxide to treat the 1,4-dioxane. Such multi-unit processes have high capital costs, are energy intensive and have inherent safety risks. The use of a single biological technology to treat both 1,4-dioxane and dilute cVOCs in groundwater would provide improved life-cycle treatment costs for the DoD at numerous impacted sites. Hence, the objective of this effort is to demonstrate and validate the use, performance, and cost of a biological fluidized bed reactor (FBR) for the treatment of these comingled chemicals.

This ESTCP project builds upon laboratory data from ESTCP Project ER-201733, the objective of which was to examine the potential for in situ biodegradation of 1,4-dioxane and cVOCs in groundwater at Naval Air Station North Island (NASNI). During this study, it was shown that isobutane (a branched alkane gas) can be used effectively as a substrate to promote cometabolic degradation of 1,4-dioxane and various cVOCs, and a new isobutane-degrading culture identified as Rhodococcus aetherivorans ENV493 (ENV493) was isolated from NASNI groundwater. Current data suggest that an ex situ biological system utilizing ENV493, or one of several other isobutane-degrading strains, for the treatment of 1,4-dioxane and dilute cVOCs to required regulatory levels is potentially both feasible and sustainable. Therefore, in this ESTCP demonstration, an isobutane-fed FBR will be tested for treatment of mixed 1,4-dioxane and cVOCs in groundwater. The FBR is an efficient fixed-film bioreactor in which a high concentration of biomass is attached onto fluidized medium. Within the fluidized medium, biological treatment of the 1,4-dioxane- and cVOC-impacted water occurs. This concept will be demonstrated through initial laboratoru characterization studies, followed by a pilot-scale demonstration at a suitable site with groundwater impacted by 1,4-dioxane and cVOCs.

A successful demonstration of the isobutane-fed FBR technology in the lab and in the field will provide DoD with a widely applicable ex situ remediation approach for plumes impacted with 1,4-dioxane and dilute cVOCs. Multiple treatment process of air stripping and advanced oxidation processes are presently the only practical method used to remove these co-occurring chemicals from groundwater. Although these technologies are effective, they can also be very expensive because of the necessary capital and electrical requirements. With the increase in the cost of electricity, as well as the complexity of operating multiple treatment processes, it is important to evaluate less expensive treatment options for these compounds. This demonstration will assess a biological treatment approach with the potential to be both effective and economical. (Anticipated Project Completion - 2025)