First Full‐Scale In Situ Propane Biosparging for Co‐Metabolic Bioremediation of 1,4‐Dioxane

Abstract

1,4‐Dioxane is an emerging contaminant of environmental concern, probable human carcinogen, and it can result in diffuse groundwater plumes and is not readily treated using common remedial techniques (e.g., via air stripping or granular activated carbon). In situ bioremediation of 1,4‐dioxane has been studied at the bench‐scale and pilot‐scale. This work documents the full‐scale application of in situ propane biosparging for the treatment of 1,4‐dioxane. The subject site is located at Vandenberg Space Force Base in California. Installation of the full‐scale treatment system came after several pilot tests (e.g., Lippincott et al. 2015), stable isotope testing (Bell et al. 2016), and rebound testing conducted from 2012 to 2016. The full‐scale propane biosparge system supplies air and propane at an average of 5 kg (11 pounds) of propane per day to a network of 97 biosparge wells, or 52 g (0.11 pounds) of propane per day per biosparge well. Additionally, a bioaugmentation culture and macronutrients were delivered to the subsurface. After approximately 6 months of operation, 1,4‐dioxane was reduced at up to 99.2%, with an average global reduction of 64.1% (excluding two anomalous monitoring wells) across a treatment area of approximately 30.5 by 61 m (100 by 200 ft).

Cometabolic Treatment of 1,4-Dioxane in Biologically Active Carbon Filtration with Tetrahydrofuran and Propane at Relevant Concentrations for Potable Reuse

“…Laboratory-scale studies have shown that propane-oxidizing bacteria can cometabolically degrade a variety of compounds, such as trichloroethylene, gasoline oxygenates, and N -nitrosodimethylamine. − Propane-stimulated 1,4-dioxane degradation has only been reported in one full-scale study by Lippincott et al, where contaminated groundwater was treated in situ by bioaugmentation of propane-degrading bacteria and sparging of propane gas down wells. In the study by Bell et al, the most contaminated wells contained ∼1000 μg/L of 1,4-dioxane, which was decreased to <2 μg/L after treatment. The successful use of propane in this setting and its ability to stimulate the degradation of low concentrations of 1,4-dioxane (i.e., micrograms per liter) make it an appealing cometabolite to further evaluate.…”

“…9 However, most cometabolic applications are currently limited to groundwater and landfill leachate and have not been tested on reuse water. 20,21 Tetrahydrofuran (THF) has been shown to effectively support cometabolic degradation of high concentrations of 1,4dioxane in landfill leachate, where the two compounds commonly occur together. 21 It is thought that structural similarities between THF and 1,4-dioxane contribute to the efficacy of THF as a cometabolite.…”

“…Theoretically, cometabolism is promising for addressing low concentrations of 1,4-dioxane because the cometabolite acts to sustain the cellular growth and enzyme production needed to drive degradation of 1,4-dioxane to low levels . However, most cometabolic applications are currently limited to groundwater and landfill leachate and have not been tested on reuse water. , …”

“…Alkanes, such as propane and ethane, have emerged in the literature as potentially effective alternative cometabolite for 1,4-dioxane degradation. ,, Propane is an easily available commodity; it can be commercially delivered, and the price per gallon has remained below $3 for the last 10 years in the United States. The solubility of propane in water is 70 mg/L at 20 °C .…”

Emerging investigator series: environment-specific auxiliary substrates tailored for effective cometabolic bioremediation of 1,4-dioxane

“…13,[15][16][17] Application of gaseous substrates has been recently demonstrated to achieve effective dioxane removal in the field. 16,18,19 Groundwater recirculation is an effective way to deliver low levels of gaseous alkanes at precise concentrations with the assistance of gas-flow controllers. 18 Compared to gaseous alkanes, liquid alcohols (e.g., 1-propanol and 1-butanol) can be advantageous considering their ease of dosing at the injection wells and monitoring through routine water sampling.…”