Development of a model for coupled colloid and contaminant transport (COLTRAP)
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Series / Report no.
Open Access
Type
Report
Language
en
Date
1998-03-31
Research Projects
Organizational Units
Journal Issue
Title
Development of a model for coupled colloid and
contaminant transport (COLTRAP)
Translated Title
Ontwikkeling van een model voor gekoppeld
transport van kolloiden en verontreinigingen
(COLTRAP)
Published in
Abstract
Het transportgedrag van verontreinigingen in poreuze
media kan worden beinvloed door binding van verontreinigingen aan
natuurlijke kolloiden. Afhankelijk van de interactie tussen
verontreinigingen, kolloiden en de vaste matrix en van chemische
omstandigheden en watersnelheden in het medium kan het transport van
verontreinigingen versneld of vertraagd worden door de aanwezigheid van
kolloiden. In dit rapport wordt een numeriek model voor gekoppeld transport
van kolloiden en verontreinigingen (COLTRAP) gepresenteerd. In het model
worden acht verschillende species (verschijningsvormen) onderscheiden. De
verontreiniging kan voorkomen in vijf verschillende vormen: 1) vrije
verontreinigingen; 2) verontreinigingen gesorbeerd aan de vaste matrix; 3)
verontreinigingen gesorbeerd aan mobiele kolloiden; 4) verontreinigingen
gesorbeerd aan immobiele kolloiden en 5) verontreinigingen die een brug
vormen tussen kolloiden en de vaste matrix. Kolloiden kunnen in drie
verschillende vormen voorkomen: 1) kolloiden in de oplossing; 2) kolloiden
direct gesorbeerd aan de vaste matrix en 3) kolloiden via verontreinigingen
gebonden aan de vaste matrix. In COLTRAP worden de interacties tussen de
verschillende species beschreven door niet-lineaire tijdsafhankelijke
(kinetische) relaties. Deze interacties worden samen met de massabalansen
voor de verschillende species simultaan opgelost. Met behulp van
analytische oplossingen is COLTRAP geverifieerd. COLTRAP is toegepast in
situaties met en zonder mobiele, stabiele kolloiden. De modelparameters
zijn functies van eigenschappen van het poreuze medium. Resultaten van de
modelsimulaties komen in het algemeen goed overeen met experimentele
resultaten. In een gevoeligheidsanalyse is aangetoond dat een snelle
doorbraak van verontreinigingen die sterk aan de vaste fase adsorberen,
optreedt in aanwezigheid van mobiele kolloiden, als verontreinigingen zich
binden aan kolloiden, en desorptie van verontreinigingen langzaam is
vergeleken met de tijd nodig voor transport over een bepaalde
afstand.
Binding of contaminants to natural colloids may significantly modify their transport behaviour through porous media. Depending on the interaction between contaminants, colloids and the solid matrix, and on chemical properties and flow rate, contaminant transport can be enhanced or retarded as a result of the presence of colloids. In this report a numerical model for coupled colloid and contaminant transport (COLTRAP) for porous media is presented. In the model eight different species are distinguished. The contaminant is distributed among five different species: 1) free contaminants in the liquid phase; 2) contaminants sorbed on the solid matrix; 3) contaminants sorbed on mobile colloids; 4) contaminants sorbed on immobile colloids; 5) contaminants acting as a bridge between the solid matrix and colloidal particles. Colloids are distributed among three species: 1) colloids in solution; 2) colloids sorbed directly on the solid matrix; 3) colloids sorbed to the solid matrix via contaminants. All interaction between the different species are described by non-linear time dependent (kinetic) relationships. In COLTRAP the mass balances for all species are solved simultaneously with interaction and degradation terms. The model is verified against analytical solutions. COLTRAP has been applied to cases with and without mobile, stable colloids. Model parameters are a function of system properties. Simulation results in general are in agreement with experimental results. Sensitivity analysis shows that breakthrough of contaminants that adsorb strongly to the solid phase can be fast in the presence of mobile colloids, if desorption of contaminants from colloids is slow compared to the time of migration.
Binding of contaminants to natural colloids may significantly modify their transport behaviour through porous media. Depending on the interaction between contaminants, colloids and the solid matrix, and on chemical properties and flow rate, contaminant transport can be enhanced or retarded as a result of the presence of colloids. In this report a numerical model for coupled colloid and contaminant transport (COLTRAP) for porous media is presented. In the model eight different species are distinguished. The contaminant is distributed among five different species: 1) free contaminants in the liquid phase; 2) contaminants sorbed on the solid matrix; 3) contaminants sorbed on mobile colloids; 4) contaminants sorbed on immobile colloids; 5) contaminants acting as a bridge between the solid matrix and colloidal particles. Colloids are distributed among three species: 1) colloids in solution; 2) colloids sorbed directly on the solid matrix; 3) colloids sorbed to the solid matrix via contaminants. All interaction between the different species are described by non-linear time dependent (kinetic) relationships. In COLTRAP the mass balances for all species are solved simultaneously with interaction and degradation terms. The model is verified against analytical solutions. COLTRAP has been applied to cases with and without mobile, stable colloids. Model parameters are a function of system properties. Simulation results in general are in agreement with experimental results. Sensitivity analysis shows that breakthrough of contaminants that adsorb strongly to the solid phase can be fast in the presence of mobile colloids, if desorption of contaminants from colloids is slow compared to the time of migration.
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