Formatted Title
Biological Degradation of High Concentrations of 1,4-Dioxane: From Laboratory to Field and Back
Background/Objectives
At a site in northwestern Europe groundwater is contaminated siginificantly with 1,4-dioxane. In 2017 a laboratory degradation study was conducted to investigate the feasibility of biodegradation for the treatment of a 1,4-dioxane contamination in a source zone. The test demonstrated that high concentrations of 1,4-dioxane could be biodegraded relatively easily in all tested biological conditions. In 2021 a field study on the site was conducted. During the field tests two crucial challenges were encountered, namely an increased pH up to about 8.9 as a result of aeration and no clear signs of biodegradation for at least 6 months. Only after additional testing did biological activity start.
The purpose of this study (field and lab) was to investigate the feasibility of bioremediation for the treatment of (high) concentrations of dioxane and get further insight into the degradation pathway and microorganisms involved.
Approach/Activities
Based on these observations additional laboratory tests were performed to gain more insight in process and effect of the increased pH, the dioxane degradation process and the involved microorganisms. Next generation sequencing (NGS) was performed to characterize the microbial community and identify the dioxane-degrading microorganisms.
Laboratory tests could confirm biodegradation, but the results were different from the first degradation test, which might be explained by a different abundance and ratio of the two most likely dioxane degrading microorganisms. The Wageningen University is currently further looking into the microbial community and the effect of different factors like pH and dissolved oxygen concentrations on the composition of the microbial community.
Laboratory tests also confirmed that already within 30 minutes of active aeration, the pH of the groundwater increased from neutral values to around 8.7 likely due to the stripping of carbon dioxide. However, it was found that an active dioxane-degrading culture was not inhibited by a short-term exposure to an elevated pH and the pH decreased in about a week to neutral values again, likely due to the production of carbon dioxide.
Based on these findings the bioreactor was started up with a passive aeration, and once biological active switched to an active aeration. In this way a long-term stable bioreactor with an removal efficiency of 99% was established. Based on NGS analyses it was also found that inoculation of the bioreactor with an active dioxane-degrading culture was not necessary and the dominant dioxane degraders were native microorganisms from the source zone.
Currently also on-site (biopiles) and in situ treatment is further investigated for treatment of the source zone.
Results/Lessons Learned
Biodegradation of high concentrations of dioxane (> 300 mg/L) was demonstrated, although the biodegradation process was different than initially thought and required more insight. Challenges in the field were overcome by additional laboratory testing and molecular analyses gave more insight into the biodegradation process and microorganisms involved. After several challenges like a high pH and the absence of clear signs of biodegradation were overcome, eventually a stable bioreactor with 99% removal efficiency was established, which is currently still active.
Laboratory tests and molecular analyses proved to be very valuable for a better understanding and control of the application of biodegradation on a field scale.