Paradis, CJ, JI Miller, J-W Moon, SJ Spencer, LM Lui, JD Van Nostrand, D Ning, AD Steen, LD McKay, AP Arkin, J Zhou, EJ Alm, TC Hazen Sustained Ability of a Natural Microbial Community to Remove Nitrate from Groundwater (2021) Groundwater [DOI]:10.1111/gwat.13132 OSTI:1807518
A consortium of ENIGMA researchers at University of Tennessee, Oak Ridge National Lab, MIT, Berkeley Lab, University of Oklahoma, and Montana State University published a field study confirming previous laboratory experiments showing that the exposure history of an environment plays a critical role in the attenuation of a groundwater contaminant. Importantly, they show that, following a community at a site over time indicates how often and how fast nitrate will be attenuated, resulting in a reduction of cost and resources for monitoring; and that native microbial communities retain the ability to reduce/remove nitrate in the prolonged absence of a limiting nutrient.
The objectives of this study were to establish an in situ natural microbial community able to remove nitrate from groundwater via the addition of an ethanol and then determine how long this ability could be sustained. The results of this study strongly suggested that the in situ ability of a natural microbial community to remove nitrate from groundwater can be sustained in the prolonged absence of an electron donor; in this case, at least 6 weeks in the absence of ethanol.
Microbial-mediated nitrate removal from groundwater is widely recognized as the predominant mechanism for nitrate attenuation in contaminated aquifers and is largely dependent on the presence of a carbon-bearing electron donor. The repeated exposure of a natural microbial community to an electron donor can result in the sustained ability of the community to remove nitrate; this phenomenon has been clearly demonstrated at the laboratory scale. However, in situ demonstrations of this ability are lacking. This is important for remediation of nitrate at sites like this DOE site where the concentration of nitrate in groundwater can be as high as 30,000 ppm (EPA drinking water standard is 10 ppm).
The objectives of this study were to establish an in situ natural microbial community able to remove nitrate from groundwater via the addition of an electron donor and then determine how long this ability could be sustained in the absence of the electron donor and elucidate the microbial mechanism(s) responsible for this ability. The results of this study strongly suggested that the in situ ability of a natural microbial community to remove nitrate from groundwater can be sustained in the prolonged absence of an electron donor; in this case, at least 6 weeks in the absence of ethanol. However, this ability was not revealed in the experiment by a sustained and selected enrichment of a planktonic microbial community based on 16S rDNA. Therefore, it is possible that such a microbial community may be present in the sessile state or that the predominant mechanism(s) of this ability exist at the enzymatic- and/or genetic-levels. Nevertheless, this study demonstrated that the exposure history of groundwater to an electron donor can play an important role in the removal of nitrate.
Terry C. Hazen, Subsurface Observatory Co-Lead
University of Tennessee & Oak Ridge National Laboratory