Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Denitrification at the microscale in treatment wetlands(Montana State University - Bozeman, College of Engineering, 2015) Spengler, Justin Warren; Chairperson, Graduate Committee: Robin Gerlach; Anne Camper (co-chair)Treatment wetlands (TWs) have been in use for over three decades for wastewater treatment, agricultural water treatment, and some industrial wastes. Thousands of TWs exist for treating wastewater globally, but the microbial processes and controls in situ primarily responsible for water treatment are poorly understood. In this study, 16 separate model TW columns consisting of three plant groups and one non-planted group were fed synthetic post-secondary wastewater with half receiving no added carbon and half receiving 0.391 g L -1 as sucrose. Core samples were taken from each of the TW columns and separated into three distinct habitats (roots, gravel, particulates). Each habitat was assayed for its ability to produce N 2O, consume N 2O, and emit N 2O, as well as for denitrification gene abundances (nirS, nirK, and nosZ) and bacterial gene abundance (16S rDNA). The addition of organic carbon to the wetland was found to increase denitrification activity and gene copy abundance in non-root fractions, but organic carbon addition did not affect the root fraction. Plant presence within the TW was found to increase gas assay and gene abundance values in non-root habitats. Differences between three plant species were minor compared to differences attributed to carbon addition and plant presence. Of all habitats, gravel was found to have the highest denitrification activity and denitrification gene copy abundance relative to the number of 16S rDNA copies, as well as the highest ratio of N 2O produced to N 2O emitted. Implications for this study suggest the gravel and root fractions should be studied in further detail for their ability to accommodate denitrifying microbes.Item An electrochemically enhanced denitrification process using biofilms(Montana State University - Bozeman, College of Engineering, 1997) Tripathi, Vijay K.Item Nitrate reduction by denitrifying bacteria within a porous medium(Montana State University - Bozeman, College of Engineering, 1998) Begaye-Ibbotson, Evangeline M.Acid processing of uranium ore resulted in aquifer contamination (nitrate, sulfate, and uranium) of the aquifer associated with the Navajo Sandstone formation at Tuba City, Arizona. The objectives of this study focused on the use of bioprocesses to remediate this aquifer contamination. The bench-scale objective of this study was to evaluate the ability of an indigenous microbial consortium to bioremediate nitrate contamination. The reduction of nitrate typically results in the production of nitrite, which under most conditions is further reduced to dinitrogen gas or ammonia. However, under some conditions inhibitory concentrations of nitrite may accumulate. Sandstone-packed columns fed with aquifer-relevant concentrations of nitrate were used to assess denitrification rates by indigenous bacteria. To enumerate denitrifying consortia used in the column experiments, most probable number (MPN) techniques were used. Sandstone-packed column influent and effluent data for nitrate, nitrite, carbon substrate and biomass concentrations were collected over time. These data were used to assess nitrate reduction rates within a sandstone column. This research demonstrates that with indigenous bacteria with stable conditions nitrate is reduced to dinitrogen forming only minimum levels of nitrite which should not inhibit sulfate-reducing bacteria (SRBs). The results of these studies indicate that bacterial denitrification has good potential as a remediation strategy for nitrate-contaminated groundwater to levels below the established regulatory limits of 44 mg/L. Field tests applications are planned for the Department of Energy UMTRA site in Tuba City, Arizona, using an extensive grid of injection and pumping wells.