Coupled iron reduction-ammonium oxidation (Feammox) in alkaline soils polluted with nitrogen
Date
2021-02-22
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0001-5700-0851
Type
Thesis
Degree Level
Masters
Abstract
Although nitrogen fertilizers help stimulate plant and microbial growth in N-limited soils, the use of excess N fertilizers to improve agricultural yield in Canada can cause adverse side effects of groundwater and surface water pollution, greenhouse gas production, soil acidification, and human health issues. Two N-removal pathways currently used to treat N-polluted wastewater and groundwater include denitrification and anaerobic ammonium oxidation (anammox). This study explored a novel anaerobic N-removal pathway that converts ammonium (NH4+) to inert nitrogen gas (N2) or nitrite (NO2-) while reducing Fe(III) to Fe(II), a.k.a. iron ammonium oxidation (Feammox) via a 118-day anaerobic incubation which included four sequential biostimulation experiments. The goal of the incubation was to identify Feammox in neutral-alkaline soil samples from a N-polluted site in Alberta by stimulating the bioremediation of NH4+. This was done amending the soils with vitamins and sources of NH4+ and Fe(III). The treatments for the anaerobic controls and soil slurries included one or more of the following: ammonium chloride (A), 2-line ferrihydrite (FH), and ferric citrate (FC). Amendments were added to these treatments in four sequential Feammox biostimulation experiments: 1) FC, FH, and A, 2) FC and FH, 3) FC and A, and 4) vitamin and molybdate solutions. The soil slurry with ferric citrate and NH4Cl amendments (S-FCA) had the most notable dissolved NH4+-N loss during the 118-day incubation, particularly when FC and A were added concurrently, i.e. a decrease of 14 ± 1.7 mg L-1 dissolved NH4+-N in the first experiment and a decrease of 13 ± 6.5 mg L-1 dissolved NH4+-N in the third experiment. S-FCA also exhibited signs of Fe(III) reduction throughout the incubation. In the incubation all samples generated minimal dissolved NO2- (0-2 mg L-1). Following the 118-day incubation the S-FCA treatment was subcultured to reproduce results; however, the subcultures did not show notable NH4+ loss, possibly due to dilution or N mineralization. Overall, this study showed a correlation between concurrent ferric citrate and NH4Cl amendments and dissolved NH4+-N loss in near-neutral anaerobic conditions; however, it did not provide clear evidence of Feammox. Additional experiments are necessary to isolate Feammox.
Description
Keywords
Nitrogen, pollution, fertilizers, bioremediation, iron, ammonium, oxidation, soil
Citation
Degree
Master of Science (M.Sc.)
Department
Soil Science
Program
Soil Science