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Coupled Hydrological and Microbiological Processes Controlling Denitrification in Constructed Wetlands
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Treatment wetlands play an important role in reducing nitrogen content in wastewater and agricultural run-off water. The main removal process is denitrification and the removal efficiency depends on the hydrological and microbiological features of the wetland, especially in terms of water residence times and denitrification rates. The aim of this thesis was to increase the understanding of the coupled hydrological and microbiological processes regulating the denitrification capacity. This was done by applying a broad spectrum of analyses methods, including tracer experiment, water flow modeling, denitrification rate measurements, and analyses of the microbial community structures. The tracer experiment and flow modeling revealed that the wetland design, especially the vegetation, largely can affect the water residence time distributions in wetlands. In the investigated wetland, vegetation dominated the water flow, explaining 60-80% of the variance in water residence times, whereas basin shape only explained about 10% of the variance, but also mixing phenomena significantly affected the residence times and could considerably delay solutes. Measured potential denitrification rates in the wetland exhibited significant spatial variations, and the variations were best described by concentration of nitrogen in sediments and water residence time. Analyses of the denitrifying bacteria populations indicated that a few key populations dominated and that the community diversity increased with decreasing nutrient levels and increasing water residence times. Moreover, it was found that denitrification rates in terms of Menten and first order kinetics can be evaluated by fitting a mathematical expression, considering denitrification and other nitrogen transforming processes to measured product formation in nitrate limited experiments.

Place, publisher, year, edition, pages
Stockholm: KTH , 2007. , p. x, 20
Series
Trita-LWR. LIC, ISSN 1650-8629 ; 2038
Keyword [en]
Constructed wetland, Residence time, water flow modeling, denitrification rate, Tracer experiment, denitrifying bacteria community structure
National Category
Oceanography, Hydrology and Water Resources
Identifiers
URN: urn:nbn:se:kth:diva-4370ISBN: 978-91-7178-663-0 (print)OAI: oai:DiVA.org:kth-4370DiVA, id: diva2:11989
Presentation
2007-05-25, V2, Teknikringen 76, Teknikringen 76, KTH, Stockholm, 13:15
Opponent
Supervisors
Note
QC 20101110Available from: 2007-05-14 Created: 2007-05-14 Last updated: 2018-01-13Bibliographically approved
List of papers
1. Controlling factors for water residence time and flow patterns in Ekeby treatment wetland, Sweden
Open this publication in new window or tab >>Controlling factors for water residence time and flow patterns in Ekeby treatment wetland, Sweden
2007 (English)In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 30, no 4, p. 838-850Article in journal (Refereed) Published
Abstract [en]

Treatment wetlands play an important role in reducing nutrient content and heavy metals in wastewater and run-off water. The treatment efficiency strongly depends on flow pattern and residence times of the water. Here, we study the impact of different factors on water flow patterns based on a tracer experiment with tritiated water in a 2.6 ha constructed wetland pond. A 2D flow and inert transport model was used to evaluate the relative importance of bottom topography, vegetation distribution, water exchange with stagnant zones and dispersion.

Results from computer simulations and independent measurements of friction losses as well as wetland geometry showed that variations in bottom topography, formed by several deep zones, decreased the variance in water residence times to a minor extent. Heterogeneity in vegetation, on the other hand, significantly contributed to the spread in water residence times and explained the multiple peaks observed in the breakthrough curves. Analyses showed that in the Ekeby treatment wetland, basin shape explained about 10% of the variance in the observed residence times, whereas vegetation explained about 60-80%. To explain all variance secondary factors were needed, such as dispersion and water exchange with stagnant zones. These were shown to contribute to the spread of residence times and primarily to the long tail of the observed breakthrough curves.

Keyword
Constructed wetland, Flow resistance, Hydraulic model, Residence time, Tracer experiment, Vegetation
National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:kth:diva-7081 (URN)10.1016/j.advwatres.2006.07.002 (DOI)000245259400009 ()
Note
QC 20100906Available from: 2007-05-14 Created: 2007-05-14 Last updated: 2018-01-13Bibliographically approved
2. Spatial variations in denitrification activity in wetland sediments explained by hydrology and denitrifying community structure
Open this publication in new window or tab >>Spatial variations in denitrification activity in wetland sediments explained by hydrology and denitrifying community structure
2007 (English)In: Water Research, ISSN 0043-1354, E-ISSN 1879-2448, Vol. 41, no 20, p. 4710-4720Article in journal (Refereed) Published
Abstract [en]

We determined spatial variations in potential denitrification activity and the controlling hydrological as well as biochemical processes in the sediments of a Swedish treatment wetland. Hydrological processes, including water residence times, were analyzed using a 2D depth-averaged flow model and the denitrifier community structure was analyzed using denaturing gradient gel electrophoreses (DGGE) of nosZ genes, encoding nitrous oxide reductase. In addition, we provide a theoretical basis for evaluation of denitrification rates useful in nitrate-limited conditions. The results demonstrate that potential denitrification rates differed significantly between the sampling locations (CV=0.34). The variations were best described by concentration of nitrogen in sediments and water residence time. DGGE analyses indicated that a few key populations dominated and that the community diversity increased with decreasing nutrient levels and increasing water residence times. Moreover, we found that denitrification rates in terms of Menten and first-order kinetics can be evaluated by fitting a mathematical expression, comparing denitrification and other nitrogen-transforming processes to measured product formation in nitrate-limited experiments.

Keyword
Bacterial community, Denitrification, DGGE, Model, NosZ, Water residence time, Wetland
National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:kth:diva-7082 (URN)10.1016/j.watres.2007.06.053 (DOI)000251627300014 ()2-s2.0-36049035934 (Scopus ID)
Note
QC 20100930. Uppdaterad från Submitted till Published (20100930).Available from: 2007-05-14 Created: 2007-05-14 Last updated: 2018-01-13Bibliographically approved

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