HR: 17:15h
AN: H34C-06    [Abstracts]
TI: Linking hydrology and denitrification kinetics in treatment wetlands
AU: Kjellin, J
EM: johan.kjellin@vv.se
AF: The Royal Institute of Technology, Dept. of Land and Water Resources Engrg Teknikringen 76, Stockholm, 10044, Sweden
AU: * Wörman, A
EM: worman@kth.se
AF: The Royal Institute of Technology, Dept. of Land and Water Resources Engrg Teknikringen 76, Stockholm, 10044, Sweden
AU: Hallin, S
EM: sara.hallin@mikrob.slu.se
AF: Swedish University of Agricultural Sciences, Det. of Microbiology Box 7025, Uppsala, 75007, Sweden
AB: A number of factors control the kinetics of denitrification in natural environments, particularly, in treatment wetlands. In order to understand and, in some sense, optimize nitrogen removal in wetlands we must link hydrological and geochemical processes. Based on a two-dimensional flow model we found that topography and vegetation distribution as well as density of vegetation are crucial reproducing the residence time distribution from a tracer test experiment. The tracer test used simultaneous injection of three labelled isotopes; H2O-3, PO4- 32 and NO3-15. Not only are the reactions constrained by the circulation patterns and water residence time, but there are essential links between vegetation as friction causing objects for the water flow and vegetation as host medium for biofilms in which denitrification can occur. This study has illuminated the importance for the treatment efficiency of the various time-scales involved in the denitrification occurring in wetlands used for treating municipal wastewater. Sampling of bed sediments in Ekeby Wetland, Eskilstuna, Sweden, were used as a basis for laboratory measurements of potential denitrification activity (PDA), evaluation of the Michaelis-Menten kinetics and denaturing gel electrophoreses (DGGE) patterns of nosZ genes, which represent the denitrifying bacterial community structure in various locations. A most essential contribution of the study is to translate such basic microbiological entities into a system response model that considers both water flow and mixing as well as microbiological reactions. The behaviour of this system model was also compared with the tracer test bfreakthrough curves. The structure and placement of vegetation is found to be of utmost importance for the contact between biofilms and nitrate-polluted wastewater and, thus, for the treatment efficiency. Erroneously placed vegetation can cause flow channelling with little utilisation of the entire wetland volume and little availability of the actively denitrifying zones for the wastewater. A statistical analysis reveals that the spatial variation of PDA is more or less linearly related to the nitrogen concentration and the flow residence time from the inlet to a particular location. The linear control on the reaction of the nitrogen concentration implies that the reaction is nitrogen limited, which has consequences for the denitrification kinetics.
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
DE: 0469 Nitrogen cycling
DE: 0497 Wetlands (1890)
DE: 1847 Modeling
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2007 Fall Meeting