Biogeochemistry of Carbon and Nitrogen in Aquatic Environments

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Nitrate Remediation

Nitrate contamination is one of our Nation's most ubiquitous groundwater contamination problems.  Project scientists have been using a two-phase approach to develop remediation strategies for nitrate contamination in subsurface water supplies.  Both approaches involve using enhanced denitrification as a mechanism for removing nitrate by reducing it to nitrogen gas. 

Nitrate Remediation - Laboratory Project

In the laboratory, we are testing a bench-scale treatment system that uses hydrogen in a bioreactor to enhance denitrification.  Hydrogen can also serve as an electron donor for hydrogen-oxidizing denitrifying (HOD) bacteria.  These microorganisms are autotrophic, requiring only carbon dioxide as a carbon source, and producing innocuous end-products (nitrogen gas and water) from the nitrate and hydrogen.  A patent application has been filed for the hydrogen bioreactor,  which has many potential applications.  For example, drinking-water suppliers are often faced with high nitrate concentrations in their source waters and the hydrogen bioreactor could be an effective tool for them to supply safe drinking water to their customers.

HOD Bioreactor After 250 Days of Operation Water and hydrogen flow in counter-current fashion. •Input is typical water supply --contains oxygen and nitrate.  •HOD is purple, non-sulfur photosynthetic bacteria grown in mixed culture.  •Purple area at bottom is nitrate-free zone where bacteria are growing on hydrogen and light in the absence of oxygen.

Funding: USGS Technology Development Office

                      USGS Toxic Substances Hydrology Program

Reports

Wahlquist, A.M., 2000, The abundance and diversity of autohydrogenotrophic denitrifying bacteria in four 

     aquifers: MA Thesis, Department of Environmental, Population, and Organismic Biology, University of Colorado,

     73 p.

Smith, R.L., Ceazan, M.L., and Brooks, M.H., 1994, Autotrophic, hydrogen-oxidizing denitrifying bacteria in 

     groundwater, potential agents for bioremediation of nitrate contamination: Applied and Environmental 

     Microbiology, v. 60, no. 6, p. 1949-1955. (on-line abstract)

Nitrate Remediation - Field Project

The potential to enhance denitrification in groundwater was investigated by adding sodium formate to the aquifer at the Cape Cod Toxics Substances Hydrology site near Falmouth, Mass.  Denitrifying bacteria are native to the subsurface, but are usually electron- donor limited in situ.  The addition of formate, which can serve as an electron donor for denitrification, overcomes that limitation, thus, increasing the extent to which nitrate can be consumed.  A two- dimensional, numerical transport model was developed for this project to simulate the in situ results.

Reports

Killingstad, M.W., Widdowson, M.A., and Smith, R.L., 2002, Modeling enhanced in situ denitrification in groundwater:

    Journal of Environmental Engineering, v. 128, no. 6, p. 491-504. (on-line abstract)

Smith, R.L., Miller, D.N., Brooks, M.H., Widdowson, M.A. and Killingstad, M.W., 2001, In situ stimulation of 

    groundwater denitrification with formate to remediate nitrate contamination: Environmental Science and 

    Technology, v. 35, p. 196-203. (on-line abstract)