State Water Resources Research Institute Program


Project ID: 2009IL171B
Title: Nitrate Remediation by Iron Redox Reactions in Soils
Project Type: Research
Start Date: 5/01/2009
End Date: 4/30/2010
Congressional District: 15
Focus Categories: Nitrate Contamination, Water Quality, Treatment
Keywords: nitrate, iron, clay, mineral, reduction
Principal Investigator: Stucki, Joseph; Day, Zachary B.; Fernandez, Fabian G.
Federal Funds: $ 27,389
Non-Federal Matching Funds: $ 54,777
Abstract: Nitrate contamination of soil, drinking water, rivers, and oceans is a serious threat to human well being and global environments. Due to extensive use in agriculture, nitrate easily permeates soils and ground water and finds its way into the ocean in almost all areas adjacent to significant human populations. Microbially mediated denitrification is a well known and heavily studied subject, but non-microbial reduction of nitrate (abiotic reduction) has received much less attention, even though its occurrence in soils has been documented. By harnessing the reducing potential of clay minerals and bacteria within the soil, we believe that nitrate concentrations can be greatly reduced.

This research seeks to determine whether reduced clay minerals will reduce nitrate and to identify the conditions under which this reaction is optimized. The central hypothesis is that reduced structural Fe in soil clay minerals creates a redox-active surface that will reduce nitrate in the surrounding waters. The objective is to identify the underlying mechanisms for the reaction of nitrate with reduced-Fe clays, with an eye to being able to devise strategies for applying this information to remove nitrate from contaminated surface and ground waters. The specific objectives are:

1)Determine the rate and extent of nitrate reduction by redox-modified clay minerals (termed here abiotic nitrate reduction).
2)Characterize the effects of pH on abiotic nitrate reduction. Identify the potential role of Fe (oxyhydr)oxides as catalysts for abiotic nitrate reduction.
3)Test the potential of Fe(0) to serve the dual role of simultaneously reducing structural Fe in the clay minerals and creating a catalytic surface for nitrate reduction.

Several soil clay minerals, selected based on a range of total Fe content, will be reduced by dithionite, bacteria, or Fe(0), then tested for reactivity with respect to abiotic nitrate reduction at different pH and temperature. The reactions will be investigated from the perspectives of both thermodynamics and kinetics. The resulting N and Fe species will be measured by standard methods, and in the case of Fe we will use Mössbauer spectroscopy at 4 K to determine the types of Fe environments that are present, including Fe in the clay mineral structure, Fe in green rust, and Fe in Fe(II) and Fe(III) (oxyhdr)oxides.

Expected results from this project are that the factors governing abiotic reduction of nitrate in soils will be understood more completely, including the relative roles and importance of oxidation state of Fe in clay minerals, pH, and Fe (oxyhydr)oxides. The benefit of this outcome will be an increased knowledge and understanding of the environment that surrounds us. The findings will be disseminated through publication in refereed journals, reports, and presentations at scientific conferences. The experiments to be performed and results to be reported will be a significant part of the M.S. thesis of the graduate student to be funded.

Progress/Completion Report, 2009, PDF

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