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Modeling Approaches for Treatment Wetlands

dc.contributor.advisorMontas, Hubert Jen_US
dc.contributor.authorCarleton, James N.en_US
dc.date.accessioned2009-10-06T06:18:12Z
dc.date.available2009-10-06T06:18:12Z
dc.date.issued2009en_US
dc.identifier.urihttp://hdl.handle.net/1903/9585
dc.description.abstractAlthough treatment wetlands can reduce pollutant loads, reliably predicting their performance remains a challenge because removal processes are often complex, spatially heterogeneous, and incompletely understood. Although initially popular for characterizing wetland performance, plug flow reactor models are problematic because their parameters exhibit correlation with hydraulic loading. One-dimensional advective-dispersive-reactive (ADE) models are also inadequate because longitudinal dispersion in wetlands is often non-Fickian as a result of steep velocity gradients. Models that make use of residence time distributions have shown promise in improving performance characterization, particularly when interdependencies of stream-tube scale velocities and reaction rate coefficients are considered (the "DND" approach). However this approach is limited to steady-state conditions, and to an assumption that transverse mixing is nil. This dissertation investigates three aspects of wetland modeling and is organized in a journal paper format. The first paper describes development of a DND model which accommodates non-steady-state conditions. The model processes flow and inlet concentration time series, and calculates as output effluent concentration time series. A version of the code allows optimization of model parameters by minimization of summed squared deviations between predicted and measured effluent concentrations. In example comparisons, model results compare favorably with measured data. The second paper develops an analytical solution to a two-dimensional advective-dispersive-reactive equation, in which all flux terms are expressed as power functions of the transverse dimension. For uniform inlet concentration this idealized heterogeneity model is similar to a DND model, but with the inclusion of transverse diffusion. An example is used to illustrate the beneficial impact that transverse mixing has on reactor performance. The third paper describes development of a model based upon a stochastic interpretation of the ADE. The solution technique that is employed results in a bicontinuum model that for steady-state conditions becomes a weighted sum of two exponential decline functions. For low and intermediate degrees of mixing, model results nicely match those of the corresponding idealized heterogeneity model, and for high mixing they match results of the corresponding one-dimensional ADE. Comparisons against data suggest the bicontinuum model may represent wetland performance better than the DND model in some but not all cases.en_US
dc.format.extent2171950 bytes
dc.format.mimetypeapplication/pdf
dc.language.isoen_US
dc.titleModeling Approaches for Treatment Wetlandsen_US
dc.typeDissertationen_US
dc.contributor.publisherDigital Repository at the University of Marylanden_US
dc.contributor.publisherUniversity of Maryland (College Park, Md.)en_US
dc.contributor.departmentBiological Resources Engineeringen_US
dc.subject.pqcontrolledEngineering, Environmentalen_US
dc.subject.pqcontrolledEngineering, Agriculturalen_US
dc.subject.pquncontrolledheterogeneityen_US
dc.subject.pquncontrolledmodelsen_US
dc.subject.pquncontrolledreactionen_US
dc.subject.pquncontrolledstochasticen_US
dc.subject.pquncontrolledtransporten_US
dc.subject.pquncontrolledwetlandsen_US


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