Sept 2007Wetland Pollutant Dynamics and Control 1 ARTIFICIAL WETLAND MODELLING FOR PESTICIDES FATE AND TRANSPORT USING A 2D MIXED HYBRID FINITE ELEMENT APPROXIMATION Part 2/2 Wanko, A., Tapia, G., Mosé, R., Gregoire, C

Sept 2007Wetland Pollutant Dynamics and Control 2

Sept 2007Wetland Pollutant Dynamics and Control 3 PESTICIDES DYNAMICS MODELING ProcessesModel Flow :Mass Balance Concept / Richards Equation Transport :Tanks (series or parallel) / Convection-dispersion Adsorption : Freundlich isotherm / linear distribution Kinetics :Zero order, first order, Michaelis – Menten.

Sept 2007Wetland Pollutant Dynamics and Control 4 PESTICIDES DYNAMICS MODELING 2D Discretization :Triangular meshs Unknown parameters : o Pressure head and solute concentrations (edges, mesh center) o Water and transport fluxes through the edges RT0 Numerical method : Mixte Hybrid Finite Element (MHFE) -Particularly well adapted to the simulation of heterogeneous flow field - The unknown parameters have the same order approximation

Sept 2007Wetland Pollutant Dynamics and Control 5 OSCILLATION CONTROL FOR ADVECTION DOMINANT PROBLEM - FLUX LIMITER - Vx,Vz the pore water velocity in x and z directions, respectively (LT -1 ), -  x,  z the grid spacing in the x and z direction, respectively (L), - Dxx, Dzz, Dxz the dispersion coefficients (L 2 T -1 ). In the literature this problem is solve by using : Operator Spliting Technique (OST) + a slope limiting tool (Ackerer et al.,1999 ; Siegel et al., 1997 ; Oltean., 2001; Hoteit et al., 2002 ; Hoteit et al., 2004 ) Advection dominant problem : Pe (Peclet number) = Numerical oscillations

Sept 2007Wetland Pollutant Dynamics and Control 6 OSCILLATION CONTROL FOR ADVECTION DOMINANT PROBLEM - FLUX LIMITER Advection dominant problem : A new approche including a flux limiter oTransport fluxes (the previous formulation) oTransport fluxes (the new formulation) The weight of advection is decreased The weight of advection is increased Water fluxes  [0 ; 1]

Sept 2007Wetland Pollutant Dynamics and Control 7 One-dimensional Transport verification – The flux limiter rr ss K s (cm/d)   cm -1 ) n h e (cm) Glendale clay loam soil parameter (Kirkland et al., 1992) ConditionHydrodynamicsTransport Initial Boundary Initial and Boundary Conditions

Sept 2007Wetland Pollutant Dynamics and Control 8 One-dimensional Transport - Flux limiter effect for different Peclet number a) max Pe=1.02 b) max Pe=1.02x10 3

Sept 2007Wetland Pollutant Dynamics and Control 9 b) max Pe=1.02x10 7 One-dimensional Transport - Flux limiter effect for different Peclet number Sensitivity analysis of the  parameter a) max Pe = 10.2 b) max Pe=1.02x10 3 c) max Pe=1.02x10 6

Sept 2007Wetland Pollutant Dynamics and Control 10 Two-dimensional Transport - Flux limiter effect for different Peclet number Two dimensional convection-dispersion problem (left) and regular mesh (right) CaseVx (m d -1 ) Vy (m d -1 )  L (m 2 d - 1 )  T (m 2 d - 1 ) Pe x x x 10 4 Parameters used in various cases

Sept 2007Wetland Pollutant Dynamics and Control 11 Two-dimensional Transport - Flux limiter effect for different Peclet number a) MHFE numerical solution b) analytical solution Vx (m d -1 ) Vy (m d -1 )  L (m 2 d -1 )  T (m 2 d -1 ) Δx (m) Δ y (m) Pe Case 1 : parameters used X Y

Sept 2007Wetland Pollutant Dynamics and Control 12 Two-dimensional Transport - Flux limiter effect for different Peclet number Case 2 : parameters used Vx (m d -1 ) Vy (m d -1 )  L (m 2 d -1 )  T (m 2 d -1 ) Δx (m) Δ y (m) Pe a) MHFE without flux limiting b) MHFE with flux limiting,  = 1 c) Analytical solution Iso-concentration lines: second test case X Y

Sept 2007Wetland Pollutant Dynamics and Control 13 Case 3 : parameters used Vx (m d -1 ) Vy (m d -1 )  L (m 2 d -1 )  T (m 2 d -1 ) Δx (m) Δ y (m) Pe Two-dimensional Transport - Flux limiter effect for different Peclet number Iso-concentration lines: second third case a) MHFE without flux limiting b) MHFE with flux limiting,  = 1 c) Analytical solution X Y

Sept 2007Wetland Pollutant Dynamics and Control 14 Adsorption model - Verification : the isotherm linear adsorption coefficient C K is solution concentration of the triangular element K [ML -3 ], S K is absorbed concentration of the triangular element K [ML -3 ]. Test case : K d = 2.38 l/kg (Atrazine ; Vryzas et al., 2007 ) Time (day) C(z = 0, t > 0) = 1.0 mg/l C(z, t = 0) = 0.1 mg/l

Sept 2007Wetland Pollutant Dynamics and Control 15 Kinetic models - Verification Simple kinetic models Conditions Zero order First order Michaelis – Menten C(t = 0, z), the initial concentration, k 2, the dissipation rate, k 1, the first order rate constant the maximum reaction rate, K m the Michaelis constant X 0 the amount of substrate to produce the initial population density

Sept 2007Wetland Pollutant Dynamics and Control 16 Kinetic models – Verification Initial conditions and kinetic parameters of the tested cases Kinetic modelsInitial concentrationKenitic parameters Without kinetic -- Michaelis – Menten Ordre z é ro 1 er ordre Zero order first order Michaelis - Menten

Sept 2007Wetland Pollutant Dynamics and Control 17 Lysimeters : Construction and instrumentation - Model Validation Aim: to elaborate a pilot-constructed wetland design based on bioaugmentation-phytoremediation coupling in order to study and improve the biological potentialities concerning the pesticides remediation CONCEPTION AND DIMENSIONS OF THE PILOT-PLANT The pilot-plant consists of 12 lysimeters Depth : 1.5m Ø : 3m 12 storage/collector tanks Depth : 2.55m Ø : 1m tank lysimeter Top view pipe The filtrating media - Coarse gravel (10/14), 25 cm depth, - Fine gravel (4/8), 25 cm depth, - Sediments («80µ), 30 cm depth, Bottom layer Top layer 9 planted bed Phragmites australis, Typha latifolia, Scirpus lacustris

Sept 2007Wetland Pollutant Dynamics and Control 18 Lysimeters : Construction and instrumentation - Model Validation INPUT -water + pollutant (glyphosate, diuron, copper) MATERIAL -12 Lysimeters -flexible feeding pipe -12 collector tanks ANALYSES Tests on influents and effluents will be made at different depths Tests on sediments Top view Cross view

Sept 2007Wetland Pollutant Dynamics and Control 19 Lysimeters : Construction and instrumentation - Model Validation ANALYSES Tests on influents and effluents will be made at different depths Tests on sediments

Sept 2007Wetland Pollutant Dynamics and Control 20