Denitrification is one of the main pathways to remove nitrate from wastewater, surface water and groundwater systems. Although denitrification has been studied for many years for water treatment systems, its behavior in natural systems especially in deep fluvial subsurface sediments that have been less affected by human activities is relatively understudied. This study investigated the denitrification process in the fine-grained sediments from the Hanford Pliocene-age Ringold Formation, which serves as an aquitard for the groundwater system at the site. The sediment samples used in the study were from redox transition zone with oxic sediment on top and reduced at bottom. The experimental results showed that nitrate was reduced by indigeneous microorganisms in the sediments via denitrification to nitrite and nitrous oxide. Unlike the result reported in the literature, abiotic reduction of nitrite was not observed. The measured rate of denitrification was much faster in the oxic sediment than that in the reduced one despite that total organic carbon content was lower in the oxic sediment. The faster denitrification in the oxic sediment was apparently caused by its higher initial biomass as revealed by ATP and microbial community analysis. This study also found that organic carbon speciation in sediment is an important factor controlling the rates of denitrification. Organic matter with more oxidized carbon leads to faster rate of denitrification. Finally, a reactive diffusion model was proposed for describing coupled denitrification kinetics and transport in the fine-grained sediments at field.

Nitrate removal by denitrification in anoxic Hanford subsurface sediment and groundwater system: Kinetics and mechanism

247th National Meeting (2014)

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