HR: 0800h
AN: B51B-0367    [Abstracts]
TI: Process-Based Modeling of Constructed Wetlands
AU: Baechler, S
EM: serge.baechler@epfl.ch
AF: Ecole polytechnique federale de Lausanne, Laboratoire de technologie ecologique, Institut des sciences et technologies de l'environnement, Lausanne, CH-1015, Switzerland
AU: Brovelli, A
EM: alessandro.brovelli@epfl.ch
AF: Ecole polytechnique federale de Lausanne, Laboratoire de technologie ecologique, Institut des sciences et technologies de l'environnement, Lausanne, CH-1015, Switzerland
AU: Rossi, L
EM: luca.rossi@epfl.ch
AF: Ecole polytechnique federale de Lausanne, Laboratoire de technologie ecologique, Institut des sciences et technologies de l'environnement, Lausanne, CH-1015, Switzerland
AU: * Barry, D A
EM: andrew.barry@epfl.ch
AF: Ecole polytechnique federale de Lausanne, Laboratoire de technologie ecologique, Institut des sciences et technologies de l'environnement, Lausanne, CH-1015, Switzerland
AB: Constructed wetlands (CWs) are widespread facilities for wastewater treatment. In subsurface flow wetlands, contaminated wastewater flows through a porous matrix, where oxidation and detoxification phenomena occur. Despite the large number of working CWs, system design and optimization are still mainly based upon empirical equations or simplified first-order kinetics. This results from an incomplete understanding of the system functioning, and may in turn hinder the performance and effectiveness of the treatment process. As a result, CWs are often considered not suitable to meet high water quality-standards, or to treat water contaminated with recalcitrant anthropogenic contaminants. To date, only a limited number of detailed numerical models have been developed and successfully applied to simulate constructed wetland behavior. Among these, one of the most complete and powerful is CW2D, which is based on Hydrus2D. The aim of this work is to develop a comprehensive simulator tailored to model the functioning of horizontal flow constructed wetlands and in turn provide a reliable design and optimization tool. The model is based upon PHWAT, a general reactive transport code for saturated flow. PHWAT couples MODFLOW, MT3DMS and PHREEQC-2 using an operator-splitting approach. The use of PHREEQC to simulate reactions allows great flexibility in simulating biogeochemical processes. The biogeochemical reaction network is similar to that of CW2D, and is based on the Activated Sludge Model (ASM). Kinetic oxidation of carbon sources and nutrient transformations (nitrogen and phosphorous primarily) are modeled via Monod-type kinetic equations. Oxygen dissolution is accounted for via a first-order mass-transfer equation. While the ASM model only includes a limited number of kinetic equations, the new simulator permits incorporation of an unlimited number of both kinetic and equilibrium reactions. Changes in pH, redox potential and surface reactions can be easily incorporated. The model has been successfully validated using published experimental data. Two measurement campaigns conducted on a CW facility from New South Wales, Australia have been used. The first set of data was used to calibrate the model, while the second trial, recorded two months later with a different loading rate, was used to identify possible changes in the wetland functioning. Further to this, a sensitivity analysis was performed to identify the main parameters controlling the system. As expected, the parameter with largest impact is oxygen mass-transfer rate.
DE: 0412 Biogeochemical kinetics and reaction modeling (0414, 0793, 1615, 4805, 4912)
DE: 0418 Bioremediation
DE: 0432 Contaminant and organic biogeochemistry (0792)
DE: 0466 Modeling
DE: 0496 Water quality
SC: Biogeosciences [B]
MN: 2007 Fall Meeting