Long term natural attenuation of 1,4-dioxane (dioxane) and its enhanced biodegradation after bioaugmentation with Pseudonocardia dioxanivorans CB1190 were assessed using flow-through aquifer columns. Natural attenuation of dioxane was not observed even after 2 years of acclimation. However, dioxane removal was observed in the bioaugmented columns (34% when the influent was 200 µg/L and 92% for 5 mg/L). The thmA gene that encodes the tetrahydrofuran monooxygenase that initiates dioxane degradation by CB1190 was only detected at the inoculation port and persisted for months after inoculation, implying the resiliency of bioaugmentation and its potential to offer long-term enhanced biodegradation capabilities. However, due to extensive clumping and limited mobility of CB1190, the augmented catabolic potential may be restricted to the immediate vicinity of the inoculation port. Accordingly, bioaugmentation with CB1190 seems more appropriate for the establishment of biobarriers. Bioaugmentation efficiency was associated with the availability of oxygen. Aeration of the column influent to increase dissolved oxygen significantly improved dioxane removal (p < 0.05), suggesting that (for sites with oxygen-limiting conditions) bioaugmentation can benefit from engineered approaches for delivering additional oxygen.
Keywords: Bioaugmentation; Dioxane; Natural attenuation; Pseudonocardia dioxanivorans CB1190.