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Modelling nitrogen transformations in free water surface wastewater treatment wetlands in Sweden
Linköping University, Department of Physics, Chemistry and Biology, Ecology . Linköping University, The Institute of Technology.
Linköping University, Department of Thematic Studies.
2001 (English)In: Water Science and Technology, ISSN 0273-1223, Vol. 44, no 11-12, 237-244 p.Article in journal (Refereed) Published
Abstract [en]

The purpose of this study was to describe and compare the fate of nitrogen (N) in two Swedish wastewater treatment wetlands in the cities of Oxelösund and Hässleholm. Specifically, we wanted to see if a fairly simple model, developed with regard to common data availability, could satisfactorily describe the concentration dynamics at the outlet from the wetlands. A first-order area-based model, with two alternative expressions for temperature dependence, was set up to describe three major processes: ammonification, nitrification and denitrification. The N concentration dynamics at the outlet of the Oxelösund wetland was not satisfactorily described, R2(NH4+-N)=0.33 and R2(NO3--N)=0.10, while the modelled concentrations corresponded quite well with measured concentrations in the Hässleholm wetland, R2(NH4+-N)=0.83 and R2(NO3--N)=0.58. The NO3--N concentrations, in both wetlands, could be slightly better described when introducing a temperature coefficient as an additional free parameter. The explained variances reported above were achieved when the model was calibrated individually for the two wetlands, when the resulting (optimised) reaction rate coefficients for each of the three processes were quite different between the two wetlands. To improve model performance, the rate equations may have to be changed to include factors in addition to concentration and temperature, such as dissolved oxygen and hydraulic efficiency. It may also be important to include other processes, such as plant uptake/decay and ammonia volatilisation.

Place, publisher, year, edition, pages
2001. Vol. 44, no 11-12, 237-244 p.
National Category
Natural Sciences
URN: urn:nbn:se:liu:diva-14075OAI: diva2:22575
Available from: 2006-10-09 Created: 2006-10-09
In thesis
1. Nitrogen removal in treatment wetlands: Factors influencing spatial and temporal variations
Open this publication in new window or tab >>Nitrogen removal in treatment wetlands: Factors influencing spatial and temporal variations
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Decreasing the nitrogen transport from land to surrounding seas is a major task throughout the world to limit eutrophication of the coastal areas. Several approaches are currently used, including the establishment of wetlands, to decrease the transport of nitrogen. Wetlands represent ecosystems where the nitrogen removal from water can be efficient given that they are appropriately designed. The aim of this thesis was to investigate and quantify the effect of critical factors that regulate the nitrogen removal in wetlands, and to develop better guidelines for wetland design. Studies were performed at different scales, from microcosms to full scale wetlands, and methods included modelling, mass balance calculations and process studies.

A first order rate model was used to simulate the nitrogen transformations in two large wetlands treating wastewater containing both ammonium and nitrate nitrogen. It was found that the dynamics of the main itrogen transformation processes could not be satisfactorily described using this approach. Large wetlands containing vegetation are complex ecosystems, and the process rates vary in both time and space. The great diversity of microenvironments favours different nitrogen processes, and large differences in potential nitrification and denitrification rates were found between different surface structures within a wetland. The results from microcosms measurements showed that the highest potential for nitrification was on surfaces in the water column, while the denitrification capacity was highest in the sediment.

For the sediment denitrification capacity, the plant community

composition was shown to be of major importance primarily by supplying litter serving as a carbon and energy source, and/or attachment surfaces, for denitrifying bacteria. Denitrification rates may be affected more than three fold by different types of litter and detritus in the sediments. Intact sediment cores from stands of the emergent plants Glyceria maxima and Typha latifolia had higher denitrification potential than sediment cores from stands of the submersed plant Potamogeton pectinatus. However, the quality of the organic material for the denitrifying bacteria was highest in G. maxima and P. pectinatus stands. All sediment cores from the wetland were limited by carbon, and the lower denitrification capacity of the submersed plant, P. pectinatus, was likely due to lower amounts of organic matter. However, in another wetland, intact cores from stands of the submersed plant Elodea canadensis had a higher denitrification capacity than the cores from stands of T. latifolia and Phragmites australis. This was possibly due to a larger biomass, and better quality, of the organic matter from that submersed specie, or to epiphytic biofilms on the living plants. Those microcosms studies showed that both the quality of the organic matter as a substrate for the microbial communities, and the amount of organic material produced were important for the denitrification capacity.

In pilot scale wetlands, the composition of the plant community was also a more important factor for high nitrate removal than the differences in hydraulic loads (equivalent of 1 or 3 d retention time), despite the cold climate. The greatest removal was found in wetlands with emergent vegetation dominated by P. australis and G. maxima, rather than in wetlands with submersed vegetation. In brief, the results presented in this thesis emphasize the importance of dense emergent vegetation for high annual nitrate removal in treatment wetlands.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2006
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1041
Wetlands, denitrification, macrophytes, nitrogen, nitrification, model, treatment wetlands, potential denitrification
National Category
Biological Sciences
urn:nbn:se:liu:diva-7564 (URN)91-85523-12-7 (ISBN)
Public defence
2006-11-10, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Available from: 2006-10-09 Created: 2006-10-09 Last updated: 2009-06-10

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