Column experiments of nonsorbing and sorbing solutes were conducted in sandy aquifer material. Re... more Column experiments of nonsorbing and sorbing solutes were conducted in sandy aquifer material. Results of the column experiments were analyzed using a numerical nonequilibrium mass transfer model (designated as dispersed flow, film and particle diffusion model, DF-FPDM), an equilibrium advection-dispersion model (designated as dispersed flow, local equilibrium model, DF-LEM) as well as a nonequilibrium two region (mobile-immobile) advection-diffusion model (designated as homogeneous solid diffusion model, HSDM). Results of the analyses revealed that in all experiments the experimental BTCs are much better predicted by the DF-FPDM than by DF-LEM and HSDM. The relative influence of different processes (film diffusion, intraparticle diffusion and dispersion) can be identified by dimensionless mass transfer parameters N F ; N S and N D : Their plausibility can be compared with the wellknown advection-dispersion-based equilibrium model. In general, spreading and asymmetry of sorbing solute BTCs can be explained with the DF-LEM and HSDM, but the identification of different processes and their influence on the total transport processes can only be ascertained with a model like DF-FPDM.
Preferential solute transport coupled with diffusion into the surrounding matrix region has been ... more Preferential solute transport coupled with diffusion into the surrounding matrix region has been examined in a silty loam soil by conducting macropore column experiments for various hydrophobic organic compounds (phenanthrene, 1, 2-DCB, TCE, carbofuran) representing the polycyclic aromatic hydrocarbons, chlorobenzenes, chlorinated solvents, and pesticides. A new and ready-to-use analytical solution was developed for this setting to model the breakthrough curves. The model accounts for advection in the macropore region, diffusion into the matrix region, and linear sorption in both regions. In this setting, hydrodynamic dispersion is negligible as proved by a comparison of an advectiondispersion model of finite pulse input. Conservative tracer experiments were predicted very well with independently determined transport parameters except for the tortuosity factor, which was used as a fitting parameter for the pore diffusion coefficient in the matrix. In case of sorbing solutes the sorption coefficient (K d) was used as additional fitting parameter. The fitted K d was 65% smaller for less sorbing compounds, e.g., carbofuran, and 80% less for strongly sorbing compounds, e.g., phenanthrene compared to the independently determined K d from batch experiments. This indicates that sorption equilibrium was not obtained completely during the matrix diffusion at the timescale of the macropore flow experiment.
Column experiments of nonsorbing and sorbing solutes were conducted in sandy aquifer material. Re... more Column experiments of nonsorbing and sorbing solutes were conducted in sandy aquifer material. Results of the column experiments were analyzed using a numerical nonequilibrium mass transfer model (designated as dispersed flow, film and particle diffusion model, DF-FPDM), an equilibrium advection-dispersion model (designated as dispersed flow, local equilibrium model, DF-LEM) as well as a nonequilibrium two region (mobile-immobile) advection-diffusion model (designated as homogeneous solid diffusion model, HSDM). Results of the analyses revealed that in all experiments the experimental BTCs are much better predicted by the DF-FPDM than by DF-LEM and HSDM. The relative influence of different processes (film diffusion, intraparticle diffusion and dispersion) can be identified by dimensionless mass transfer parameters N F ; N S and N D : Their plausibility can be compared with the wellknown advection-dispersion-based equilibrium model. In general, spreading and asymmetry of sorbing solute BTCs can be explained with the DF-LEM and HSDM, but the identification of different processes and their influence on the total transport processes can only be ascertained with a model like DF-FPDM.
Abstract Nonlinear sorption of hydrophobic organic pollutants in soils and sediments can be descr... more Abstract Nonlinear sorption of hydrophobic organic pollutants in soils and sediments can be described by a combination of partitioning and adsorption (pore-filling) mechanisms. Both the partitioning and the pore-filling models plot sorptive uptake vs. solubility-normalized ...
This paper deals with an environmental impact assessment of low water flow in the river Ganges du... more This paper deals with an environmental impact assessment of low water flow in the river Ganges during a dry period at the Khulna and Mongla port areas in southwestern Bangladesh. Large-scale surface water withdrawal in India after commissioning the Farakka Barrage causes a drastic fall in the Ganges low-flow condition within the Bangladesh territory during every dry period. The average lowest discharge in the Ganges is 552 m 3 /s, which is about 73% less than that in the pre-Farakka time. This has caused the deterioration of both surface and groundwater quality of the study area. Salinity is the principal cause of water quality degradation in the area. Present observation shows that the surface water of the area is sulphate-chloride dominated, which signifies high salinity whereas the groundwater is categorized as of medium to high salinity. To maintain the Rupsa River's maximum salinity below 1000 mS/cm the discharge in the Ganges should be F1500 m 3 /s, whereas that at Garai basin is F10 m 3 /s. If this present situation continues it will be a crippling blow to the environment of the area in the long term. An integrated multidisciplinary approach to hydrogeological research is urgently required to salvage the area from further deterioration.
While the pH effect on sorption equilibrium of weak acids on natural sorbents was investigated in... more While the pH effect on sorption equilibrium of weak acids on natural sorbents was investigated in a number of studies, less is known about the pH dependence of sorption kinetics. This paper investigates the impact of pH on sorption kinetics during the transport of some selected phenols through a sandy aquifer material. Breakthrough curves measured in column experiments were analyzed using a mass transfer based nonequilibrium model designated as dispersed flow, film and particle diffusion model (DF-FPDM). In this model, the rate limiting intraparticle diffusion is characterized by the mass transfer coefficient, k S a V , which can be determined from breakthrough curves by curve fitting. The experimental results indicate that the k S a V is pH-dependent and inversely correlated with the pH-dependent distribution coefficient, K d,app. Regression equations are presented that may be used to estimate approximate values of intraparticle mass transfer coefficients on the basis of experimentally determined or LFER predicted distribution coefficients.
Column experiments of nonsorbing and sorbing solutes were conducted in sandy aquifer material. Re... more Column experiments of nonsorbing and sorbing solutes were conducted in sandy aquifer material. Results of the column experiments were analyzed using a numerical nonequilibrium mass transfer model (designated as dispersed flow, film and particle diffusion model, DF-FPDM), an equilibrium advection-dispersion model (designated as dispersed flow, local equilibrium model, DF-LEM) as well as a nonequilibrium two region (mobile-immobile) advection-diffusion model (designated as homogeneous solid diffusion model, HSDM). Results of the analyses revealed that in all experiments the experimental BTCs are much better predicted by the DF-FPDM than by DF-LEM and HSDM. The relative influence of different processes (film diffusion, intraparticle diffusion and dispersion) can be identified by dimensionless mass transfer parameters N F ; N S and N D : Their plausibility can be compared with the wellknown advection-dispersion-based equilibrium model. In general, spreading and asymmetry of sorbing solute BTCs can be explained with the DF-LEM and HSDM, but the identification of different processes and their influence on the total transport processes can only be ascertained with a model like DF-FPDM.
Preferential solute transport coupled with diffusion into the surrounding matrix region has been ... more Preferential solute transport coupled with diffusion into the surrounding matrix region has been examined in a silty loam soil by conducting macropore column experiments for various hydrophobic organic compounds (phenanthrene, 1, 2-DCB, TCE, carbofuran) representing the polycyclic aromatic hydrocarbons, chlorobenzenes, chlorinated solvents, and pesticides. A new and ready-to-use analytical solution was developed for this setting to model the breakthrough curves. The model accounts for advection in the macropore region, diffusion into the matrix region, and linear sorption in both regions. In this setting, hydrodynamic dispersion is negligible as proved by a comparison of an advectiondispersion model of finite pulse input. Conservative tracer experiments were predicted very well with independently determined transport parameters except for the tortuosity factor, which was used as a fitting parameter for the pore diffusion coefficient in the matrix. In case of sorbing solutes the sorption coefficient (K d) was used as additional fitting parameter. The fitted K d was 65% smaller for less sorbing compounds, e.g., carbofuran, and 80% less for strongly sorbing compounds, e.g., phenanthrene compared to the independently determined K d from batch experiments. This indicates that sorption equilibrium was not obtained completely during the matrix diffusion at the timescale of the macropore flow experiment.
Column experiments of nonsorbing and sorbing solutes were conducted in sandy aquifer material. Re... more Column experiments of nonsorbing and sorbing solutes were conducted in sandy aquifer material. Results of the column experiments were analyzed using a numerical nonequilibrium mass transfer model (designated as dispersed flow, film and particle diffusion model, DF-FPDM), an equilibrium advection-dispersion model (designated as dispersed flow, local equilibrium model, DF-LEM) as well as a nonequilibrium two region (mobile-immobile) advection-diffusion model (designated as homogeneous solid diffusion model, HSDM). Results of the analyses revealed that in all experiments the experimental BTCs are much better predicted by the DF-FPDM than by DF-LEM and HSDM. The relative influence of different processes (film diffusion, intraparticle diffusion and dispersion) can be identified by dimensionless mass transfer parameters N F ; N S and N D : Their plausibility can be compared with the wellknown advection-dispersion-based equilibrium model. In general, spreading and asymmetry of sorbing solute BTCs can be explained with the DF-LEM and HSDM, but the identification of different processes and their influence on the total transport processes can only be ascertained with a model like DF-FPDM.
Abstract Nonlinear sorption of hydrophobic organic pollutants in soils and sediments can be descr... more Abstract Nonlinear sorption of hydrophobic organic pollutants in soils and sediments can be described by a combination of partitioning and adsorption (pore-filling) mechanisms. Both the partitioning and the pore-filling models plot sorptive uptake vs. solubility-normalized ...
This paper deals with an environmental impact assessment of low water flow in the river Ganges du... more This paper deals with an environmental impact assessment of low water flow in the river Ganges during a dry period at the Khulna and Mongla port areas in southwestern Bangladesh. Large-scale surface water withdrawal in India after commissioning the Farakka Barrage causes a drastic fall in the Ganges low-flow condition within the Bangladesh territory during every dry period. The average lowest discharge in the Ganges is 552 m 3 /s, which is about 73% less than that in the pre-Farakka time. This has caused the deterioration of both surface and groundwater quality of the study area. Salinity is the principal cause of water quality degradation in the area. Present observation shows that the surface water of the area is sulphate-chloride dominated, which signifies high salinity whereas the groundwater is categorized as of medium to high salinity. To maintain the Rupsa River's maximum salinity below 1000 mS/cm the discharge in the Ganges should be F1500 m 3 /s, whereas that at Garai basin is F10 m 3 /s. If this present situation continues it will be a crippling blow to the environment of the area in the long term. An integrated multidisciplinary approach to hydrogeological research is urgently required to salvage the area from further deterioration.
While the pH effect on sorption equilibrium of weak acids on natural sorbents was investigated in... more While the pH effect on sorption equilibrium of weak acids on natural sorbents was investigated in a number of studies, less is known about the pH dependence of sorption kinetics. This paper investigates the impact of pH on sorption kinetics during the transport of some selected phenols through a sandy aquifer material. Breakthrough curves measured in column experiments were analyzed using a mass transfer based nonequilibrium model designated as dispersed flow, film and particle diffusion model (DF-FPDM). In this model, the rate limiting intraparticle diffusion is characterized by the mass transfer coefficient, k S a V , which can be determined from breakthrough curves by curve fitting. The experimental results indicate that the k S a V is pH-dependent and inversely correlated with the pH-dependent distribution coefficient, K d,app. Regression equations are presented that may be used to estimate approximate values of intraparticle mass transfer coefficients on the basis of experimentally determined or LFER predicted distribution coefficients.
Uploads
Papers by Mokhles Rahman