Bioaugmentation and Propane Biosparging for In Situ Biodegradation of 1,4-Dioxane

Abstract

Propane biosparging and bioaugmentation were applied to promote in situ biodegradation of 1,4‐dioxane at Site 24, Vandenberg Air Force Base (VAFB), CA. Laboratory microcosm and enrichment culture testing demonstrated that although native propanotrophs appeared abundant in the shallow water‐bearing unit of the aquifer (8 to 23 ft below ground surface [bgs]), they were difficult to be enriched from a deeper water‐bearing unit (82 to 90 feet bgs). Bioaugmentation with the propanotroph Rhodococcus ruber ENV425, however, supported 1,4‐dioxane biodegradation in microcosms constructed with samples from the deep aquifer. For field testing, a propane‐biosparging system consisting of a single sparging well and four performance monitoring wells was constructed in the deep aquifer. 1,4‐dioxane biodegradation began immediately after bioaugmentation with R. ruber ENV425 (36 L; 4 × 109 cells/mL), and apparent first‐order decay rates for 1,4‐dioxane ranged from 0.021 day−1 to 0.036 day−1. First‐order propane consumption rates increased from 0.01 to 0.05 min−1 during treatment. 1,4‐dioxane concentrations in the sparging well and two of the performance monitoring wells were reduced from as high as 1090 µg/L to <2 µg/L, while 1,4‐dioxane concentration was reduced from 135 µg/L to 7.3 µg/L in a more distal third monitoring well. No 1,4‐dioxane degradation was observed in the intermediate aquifer control well even though propane and oxygen were present. The demonstration showed that propane biosparging and bioaugmentation can be used for in situ treatment of 1,4‐dioxane to regulatory levels.

Stable Isotope Probing to Confirm Field‐Scale Co‐Metabolic Biodegradation of 1,4‐Dioxane

“…This suggests that 1,4‐dioxane was mineralized to inorganic carbon as a result of the propane biosparge operation by replicating the optimized parameters described by Lippincott et al. () for two months of additional operation.…”

“…The Phase 1 biosparge demonstration (Lippincott et al., ) operated for approximately eight months, and resulted in 1,4‐dioxane concentration decreases of 95 to >99 percent in influenced wells (113 μg/L to 1,090 μg/L on Day 14; 1.0 μg/L to 7.4 μg/L on Day 245 [Lippincott et al., ]). Due to the beneficial treatment from the Phase 1 biosparge, the baseline 1,4‐dioxane concentrations ahead of the Phase 2 biosparge were lower (3.0 μg/L to 330 μg/L in Phase 2 compared to 113 μg/L to 1,090 μg/L in Phase 1).…”

“…The Phase 2 biosparge operated for approximately two months, and resulted in an approximately 45 to 83 percent decrease in 1,4‐dioxane concentrations in influenced wells (Exhibits and ). While no notable decrease in 1,4‐dioxane occurred at 24‐MW‐5A during the Phase 1 biosparge (346 μg/L on Day 14; 323 μg/L on Day 245 [Lippincott et al., ]), an approximately 45 percent reduction occurred during the Phase 2 biosparge (Exhibits and ). The observed difference in concentration reduction at 24‐MW‐5A, located within the intermediate zone above the target deep zone treatment area, may be due in part to the 2014 intermediate zone biosparge conditioning the bacteria in the vicinity of 24‐MW‐5A.…”

“…Lippincott et al. () acknowledged the abundance of propane monooxygenase genes in groundwater did not correlate to levels of propane consumption or decreases in 1,4‐dioxane concentrations and attributed it to an underestimation in the soil‐bound microbial population. The SIP testing employed in the work described herein provides a means of unequivocally demonstrating transformation of 1,4‐dioxane, which is interpreted to be the result of biodegradation.…”

Evaluation of microbial transport during aerobic bioaugmentation of an RDX-contaminated aquifer

“…Bioaugmentation is an accepted treatment option with commercially available inocula targeted to biodegrade halogenated hydrocarbons (Schaefer et al 2010;Stroo et al 2013), aromatic hydrocarbons (Da Silva and Alvarez 2004), gasoline oxygenates (Salanitro et al 2000), and 1,4-dioxane (Lippincott et al 2015) among others. Bioaugmentation has not been used to treat explosive-contaminated groundwater, despite an increase in knowledge of RDX biodegradation in the past fifteen years (Andeer et al 2009;Bernstein et al 2011;Crocker et al 2006;Fuller et al 2009Fuller et al , 2010Hatzinger and Lippincott 2012;Livermore et al 2013;Seth-Smith et al 2008).…”