DE19800887B4 - Scalable, semi-open column device for the detection of chemical, physical and hydraulic parameters of water and mass transport in porous media - Google Patents

Abstract

Scalable, semi-open column device for the detection of chemical, physical and hydraulic parameters of water and mass transport in porous media, consisting of
a sample cylinder (5) with side-mounted bores that receive mini-tensiometer (4) and TDR probes (12),
a divisible pillar base (10), consisting of
a cover ring (21) which encloses the lower end of the sample cylinder (5) flush and watertight,
a base plate (24) having a column outlet (8) and a bleed screw (9), a porous plate (7), said porous plate (7) being received by said base plate (24) so as to support said lower end of said sample cylinder (24). 5), wherein the base plate (24) can be removed from the cover ring (21),
a headspace fumigation and gas sampling chamber (3) containing horizontal gas inlet ports (29) allowing fumigation and gas sampling whereby the headspace fumigation and gas sampling chamber (3) can be sealed to the top of the sample cylinder (5) .
a sprinkler unit (2) with a column inlet (1) and ...

Description

Laboratory column experiments make an important contribution to understanding the processes of water and mass transfer and the identification of their coefficients and Parameter in porous Media. Under porous Media are quite generally both soils, as well as sediments and Aquifers understood. In particular, laboratory column experiments will be used to determine mobility reactive substances under dynamic flow conditions (Klute and Dirksen 1986; Kool et al. 1989; Biggar and Nielsen 1962; Schweich and Sardin 1981, Bürgisser et al. 1994). Future become column experiments a prominent role in the assessment and assessment of endangerment of surface and groundwaters by human and ecotoxicological gain critical substances. Beyond the risk assessment based on column experiments Data collected increasingly also in the framework of the intervention analysis, Environmental Impact Assessment (EIA) and the Environmental Impact Assessment (UVU) for assessment and critical evaluation. The insight, that data for estimation mobility of pollutants that are based solely on shaking experiments, not sufficient for the Assessment of the spread of pollutants in porous media have now led to that too in the relevant Standards for the assessment of hazards Fixed column experiments become (DIN, EN). For this reason, pillars are no longer just have the status of pure research tools, but also on a daily basis Routine of chemical laboratories, but also of engineering firms in the field Contaminated Sites, Risk Assessment, EIA, UVU and environmental audit count. As results from column experiments in the context of litigation proceedings thereby also in court gain in importance comes to those laboratory pillar systems, the high technical, but also qualitative and practical Meet requirements and flexible but can be used extensively in terms of personnel and costs size Meaning too. So should the economic forecast for the commercial The success of the laboratory column system presented here is quite positive fail.

The Investigation of mobility of reactive substances takes place by the inclusion of so-called Breakthrough curves (DBK). DBK are concentration-time courses that at a certain but fixed location of a soil sample (column) - usually at Column exit - metrological be determined. The recorded DBK then becomes one subjected to mathematical-numerical analysis, in the course of which Method of nonlinear compensation calculation the corresponding mobility parameters be identified (parameter determination by inverse modeling). The shape and the curvature properties a breakthrough curve as a result of the selected influence boundary condition a function of the characteristics and properties of the interactions the substance under consideration with the components of the porous medium. So far, the vast majority Number of column experiments carried out under the following experimental conditions: stationary, saturated flow conditions, Convection-dominated transport regime (Peclet numbers »10). (please refer z. B. Dunnivant et al. 1992; Johnson and Amy 1995; Cernik et al 1994). This experimental test is to be referred to as classic experiment design. Experiments according to classic experimental designs are quick to perform, inexpensive, and have only low requirements for the measuring and control devices, the to carry out of the experiment are necessary.

by virtue of the relatively simple experiment However, the application of classic experiment design is limited to the determination of parameters for linear and spontaneously interacting substances in water-saturated Environments. In all other cases be the DBK by the overlay various other mutually reinforcing or competing ones Processes affected. In general leads the overlay of Processes in the classical experimental design to DBK, whose numerical Analysis not in clearly identifiable and therefore interpretable Results result (Totsche, 1995). A solution of uniqueness and Identification problem poses the application of more complex experiment designs (Brusseau et al., 1989; Grolimund et al., 1995, Totsche et al. 1997). However, the more complicated the experimental design, the more more complex and technically advanced must the experimental apparatus be. Laboratory column systems, the carrying support such elaborate design, are accordingly highly sophisticated research tools technical requirements for the operator. Mostly focused the development is based on specific research requirements and questions. Other important aspects such as robustness, practicality and easy handling. For these reasons, the implementation of Laboratory column experiments on research facilities with trained and competent staff limited.

In the following, a computer-controlled semi-open laboratory soil column system (LBSS) for the detection of chemical, physical and hydraulic parameters of water and mass transport in porous media is presented, which describes the application and implementation of user-defined Ex allowed perimentdesings. The facility to be presented allows experiments under saturated and partially saturated flow conditions, as they apply to aquifers and sediment materials on the one hand and soils on the other. Stationary (divergent flow) or transient (divergent flow) water flow conditions can be realized. The influence boundary conditions are freely selectable. The plant to be presented solved a number of known problems of existing column plants: For example, the plant can be used to create a rain boundary condition typical of natural systems. The division of the column foot allows an undisturbed, stratified sampling of the sample material, since no destructive sampling must be performed. The developed headspace allows a continuous gas space sampling, which is especially necessary for experiments with volatile substances. In the development of the apparatus to be presented special attention was paid to a user-friendly and easy handling, to implement even complicated experimental design with little effort.

The Plant was designed to perform different research and investigation tasks to serve:

Determination of mobility parameters in saturated and partially saturated porous Media:

 sorption isotherms, Distribution equilibria, exchange processes, the following characteristics can have: Linear and nonlinear characteristics, balance and nonequilibrium, hysteresis,

Determination more effective Material constants:

Diffusion coefficient, fugacity, Sorption exchange parameters

Determination of material functions for porous media:

Water content Water voltage characteristic differently textured porous Media, hydraulic conductivity coefficient kf of sediments and aquifers, saturated and unsaturated water conductivity of soils, Etc.

• • die ungestörte, schichtenweise Entnahme des Probenmaterials
• • eine kontinuierliche Gasraumbeprobung (z.B. für die Analyse flüchtiger Substanzen)
• • eine teilgesättigte Experimentführung
• • frei wählbare Einflußrandbedingungen (z.B. natürliche Regenrandbedingung durch den Sprinkler)
• • eine computergestützte Datenaufnahme und Steuerung
• • eine Gradientensteuerung der angelegten Randbedingungen (Konzentration in den Lösungen, Druckrandbedingungen)

The device specifically allows:

• • the undisturbed, stratified removal of the sample material
• A continuous gas space sampling (eg for the analysis of volatile substances)
• • a partially saturated experiment
• • freely selectable influence boundary conditions (eg natural rain boundary condition by the sprinkler)
• • a computer-aided data acquisition and control
• A gradient control of the applied boundary conditions (concentration in the solutions, pressure boundary conditions)

• • Sprinklereinheit zur Beregnung des pörosen Mediums
• • Headspace-Einheit zur Gasraumbeprobung.
• • Geteilter Säulenfuß zur ungestörten Beprobung des porösen Untersuchungsguts.
• • Schnellverschluß zur einfachen Handhabung.

The presented semi-open laboratory column system contains the following technical innovations:

• • Sprinkler unit for sprinkling the porous medium
• • Headspace unit for gas space sampling.
• • Divided pedestal for undisturbed sampling of the porous specimen.
• • Quick release for easy handling.

One embodiment The invention is illustrated in the figures and will be described in more detail below.

It demonstrate:

1 Schematic representation of the apparatus construction. A: storage vessels, B: peristaltic pump, C: laboratory columns, D: vacuum pump and reservoir; E, F: flow cells, G: fraction collector; H: AD / DA conversion and measurement control unit; P1: transport hoses; P2: Vacuum hoses

2 Detailed view of the half-open laboratory column system (section)

3 Detailed view of the sprinkler unit: side view (section)

4 Detailed view of the sprinkler unit: side view and front view

5 Detailed view of the headspace: side view (section)

6 Detailed view of the column foot (cut)

The entire experimental setup ( 1 ) consists of four essential components: the guard column system, the semi-open laboratory floor column, the analogue / digital - digital / analogue conversion and data acquisition unit and the post-column system.

The guardrail system

The individual components of the guard column system are:
The storage vessels (A)
The gradient former (L)
The transport hoses (P1)
The peristaltic pump (B)

The Storage vessels (A): These are commercially available laboratory goods that are available from specialist retailers can be obtained. Depending on the chemical substances, glass, PE, PTFE or steel bottles used.

gradient former (L): The term gradient former refers to the chemical identity the percolation solution, which is given up on the sample. In special conditions It may be necessary to use chemical parameters such as pH, electrolytic conductivity or chemical composition during of the experiment to vary. This task is taken over by the gradient former. The gradient former (L) consists essentially of computer-controlled 24V DC solenoid valves (Labokron, Sinsheim, Germany), which with a computer-controlled peristaltic pump (B) are combined. A smooth chemical gradient can thus be achieved by mixing two Solutions, come from the different storage vessels, getting produced.

Vacuum chamber problem and peristaltic pump (B). The peristaltic pump (B) will as well as the supply of percolation solution as well as for the removal of the eluate used. There is a commercial peristaltic Pump used (Minipuls 3, Gilson, Middleton, WI, USA).

By the use of the peristaltic pump at the column exit was a simple Solution of the Vacuum chamber problem found: A major problem with the execution unsaturated column experiments lies in it, that to maintain the unsaturated flow conditions a negative pressure at the column outlet must be created but at the same time the outflowing Effluentlösung to the flow cells and must be forwarded to the fraction collector. Commercially available fraction collectors However, they are open systems that are subject to the atmospheric pressure. To maintain the negative pressure must therefore a complete encapsulation of the column exit, the flow cells and the fraction collector into an evacuable chamber be (Zurmühl et al. 1995). However, this requires a robust and solid construction a relatively large vacuum chamber, because the partial evacuated chamber due to high ambient pressures the pressure gradient atmosphere-vacuum chamber must resist. Such constructions are vulnerable and usually very expensive. A simple and workable solution of the The problem is the use of another peristaltic Pump at the column outlet The pump head serves as a pressure resistor, the negative pressure, at the column exit is applied, from the atmospheric pressure decoupled. Again, the peristaltic pump Minipulse 3 comes They resist pressure gradients of up to 0.5 MPa can.

Transport hose system (P1). The choice of transport hoses depends on the chemical properties of the substances. For hydrophobic substances are annealed, carbon-free, stainless steel capillaries used (Chromatography trade Müller GmbH, Fridolfing). PTFE elastomer tubes are for the peristaltic pump used. (Isoversinic, Gilson Middleton, WI, USA). inorganic solutions are transported in medical tubing systems (Malinckrodt, Hennef-Sieg).

semi-open Laboratory soil column system

essential The aim of the development work was the construction of a practicable and easy-to-use column system, that's the implementation both from research experiments and routine examinations allows. Particular attention has been paid to the construction of (i) the solution application device, (ii) the support a quick and easy column insertion and assembly without the use of screws, (iii) the construction a column outflow system to avoid the vacuum chamber problem

The individual components of the semi-open laboratory flooring column system are:
the sprinkler unit ( 2 )
the headspace ( 3 )
the sample cylinder ( 5 )
the pedestal ( 10 )

The individual parts are put together and connected by three snap fasteners ( 11 ) ( 2 ).

Sprinkler unit: The sprinkler unit ( 2 ) allows the realization of ponding infiltration, water-saturated experiments as well as rainfall conditions (sprinkling infiltration, water-saturated experiments). The innovation lies in the possibility of giving up the percolation solution to the soil sample through a specially designed sprinkler (irrigation, rainfall condition, 3 . 4 ). As individual sprinklers, no nozzles or syringes are used, but glass capillaries ( 16 ), as they are manufactured for the production of gas-tight syringes. Glass capillaries ( 16 ) have several advantages over nozzles or simple steel capillaries, such as those used for medical syringes: The end face represents a well-defined silicate surface, at which equal-volume solution drops are formed form, which breaks off at a certain limit volume. Thus, a homogeneous, area-proportional sprinkling of Probegutoberfläche is guaranteed, an important prerequisite for the formation of a uniform flow field. In addition, only very small pressure difference is needed for irrigation. In general, 2 cm of overflow height is sufficient to ensure continuous flow. When using nozzles on the other hand considerable pressures must be spent by el. Or mechanical pumps. When using stainless steel capillaries, the small wall thickness has a disadvantage: The drop shape and size depends solely on the opening geometry of the stainless steel capillary, which can vary considerably in part: A uniform irrigation is not guaranteed.

The glass capillaries ( 16 ) are sold by the meter, are cut to 1.5 cm pieces. The end faces of the capillaries are then ground, deburred and polished. In this way, smooth, uniform Strinseiten be obtained for individual capillaries. A certain number of these capillaries ( 16 ) is now in the holes of a prepared stainless steel plate ( 15 ) glued. The arrangement and number of capillaries ( 16 ) on this plate ( 15 ) is a function of the cross-sectional area of the sample cylinder ( 5 ) and the desired volume flow density range. Currently available are small sprinklers for sample cylinder with 5 cm diameter with 7 pieces and 9 pieces of individual sprinkler capillaries and medium sprinklers with 12 pieces and 15 pieces of individual sprinkler capillaries.

Headspace ( 5 ): The headspace ( 3 ) is placed between sprinkler unit ( 2 ) and sample cylinder ( 5 ). It is used for gas space sampling for experiments with volatile substances. Due to its structural characteristics, the headspace ( 3 ) but also used to guide a gas flow over the sample to dissipate gases formed in the sample and subjected to chemical analysis. A gas-tight connection with sprinkler unit ( 2 ) and sample cylinder ( 5 ) is protected by O-ring seals ( 18 ) guaranteed.

Sample Cylinder: The Sample Cylinder ( 5 ) is used to record the sample, this may be sediment, aquifer materials or soil samples. By means of an appropriate device undisturbed soil samples can also be examined. As sample cylinder ( 5 ) Depending on the substances to be examined, stainless steel cylinders or acrylic glass cylinders are used. It can sample cylinder ( 5 ) of any length and with different diameters. A special cylinder allows the use of liner samples. In the wall of the sample cylinder ( 5 ) are appropriate and lockable holes for different sensors embedded. They allow the recording of TDR probes ( 12 ) and micro tensiometers ( 4 and others

Divisible pedestal ( 6 ): The pedestal ( 10 ) forms the lower end of the laboratory flooring column system. It serves the removal of the percolation solution, the transfer of negative pressure and allows a simple, depth-dependent sampling of the sample after completion of the experiment due to its division: The disadvantage of previous systems was that the sample could be subjected only to disrupted chemical analysis after completion of the experiment , This is due to the fact that to ensure the gas and water-tightness of the laboratory flooring column system the sample cylinder ( 5 ) with considerable force in the with O-ring seals ( 6 ) equipped pedestal ( 10 ) had to be pressed. After completion of the experiment, sampling of the sample could only be done from above (spoon sampling). The two-part construction eliminates this disadvantage: the lower part of the pedestal, the pedestal base plate ( 24 ), for receiving the porous plate ( 7 ), can from the Säulenfußdeckring ( 21 ) are removed. The pillar foot cover ring ( 21 ) encloses flush and waterproof the sample cylinder ( 5 ). After this has been done, the sample can be removed with a specially produced stamp from the sample cylinder ( 5 ) are expressed upward with little effort.

AD / DA conversion and data acquisition unit

The individual components of the AD / DA conversion and data acquisition unit are:
the multi-volt power supply
the measuring computer

A commercially available IBM-compatible computer (Intel 80486DX processor, 66MHz, 16MB of memory, 1GB of hard disk) is at the heart of the AD / DA conversion and data acquisition unit. The computer operates under Microsoft MS-DOS 6.22 and Windows 95 (Microsoft Inc ., Redmont, WA, USA). The data acquisition software used is Testpoint, version 2.0, of the Capital Equipment Corporation (CEC, Burlington, Massachusetts, USA). It also uses a CIO DAS 16 / F AD / DA computer card and a CIO-EXP32 / 16 multiplexer board (Computer Boards Inc., Mansfield, Ma, USA). To supply the sensors (TDR ( 12 ), Pressure transducer, micro-tensiometer ( 4 ), pumps, and solenoid valves with the necessary voltages and currents, a multi-voltage supply has been designed and built (5V, 10V, + -15V). All sensors are supplied with their own power supply, the measuring signals are transferred to the data acquisition computer via a galvanic isolation.

Nachsäulensystem

The individual components of the post column system are:
the vacuum reservoir and vacuum pump (D)
the flow cells (E, F)
the fraction collector (G)
the peristaltic pump (B)

Unferdruckreservoir and vacuum pump (D): As a vacuum reservoir is a 50 liter aluminum drum (Maisel, Bayreuth), which has been equipped with 6 flanges for coupling vacuum hoses. A commercially available membrane pump (KNF Neuberger, Laborcenter, Nuremberg, vacuum capacity 100 mbar abs., Flow rate 15 L min ^-1 ) serves to provide the vacuum. Vacuum fluctuations due to the regulation are compensated by the 50 liter aluminum barrel. The vacuum measurement is carried out using two Honeywell 176PC14HG2 pressure transducers (IBA, Forchheim), one of which is mounted in the vacuum reservoir and a second one on the pedestal. As vacuum hoses (P2) commercially available PVC vacuum hose fabric is used (Labor Center, Nuremberg).

The flow-through (E, F): The measurement of temperature and electrochemical parameters in the percolate of the column over electrochemical sensors (pH, electrolytic conductivity, Electrodes, etc.), which are introduced into flow cells (E, F). In order to avoid a mutual interference of the sensors, was for every Measured variable one specific flow cell constructed, which was adapted to the geometry of the sensor. The influx level the flow cell is below the outflow level to a dry falling of the sensors and associated erroneous measurements to prevent. The flow cells (E, F) are made of different materials, and thus as well as organic as well inorganic substances suitable.

fraction collector (G): A commercial fraction collector (Foxy, Isco Inc., Nebraska, USA) becomes the separation of individual effluent fractions used.

literature

• BIGGAR J.W., and NIELSEN D.R. (1962) Miscible displacement: II. Behavior of tracers. Soil Sci. Soc. Amer. Proc. 26, 125-128.
• BRUSSEAU M.L., RAO P.S.C., JESSUP R.E., and DAVIDSON J. M. (1989) Flow interruption: A method for investigating sorption Nonequilibrium. J. Contam. Hydrol. 4, 223-240.
• Bürgisser C.S., CERNIK M., BORKOVEC M., and STICHER H. (1993) Determination of Nonlinear Adsorption Isotherms from Column Experiments: An Alternative to Batch Studies. Environ. Sci. Technol. 27 (5), 943-948.
• CERNIK M., BARMETTER K., BORKOVEC M., and STICHER H. (1994) Multicomponent transport of major cations in columns. In transport and reactive processes in aquifers (eds.DRACOS T.N., and STAUFFER F.), pp. 119-124. A. A. Balkema.
• DUNNIVANT F.M., JARDINE P.M., TAYLOR D.L., and MCCARTHY J. F. (1992) Cotransport of cadmium and hexachlorobiphenyl by dissolved organic carbon through columns containing aquifer material. Environ. Sci. Technol. 26, 360-368.
• ENFIELD C.G., BENGTSON G., and LINDQUIST R. (1989) Influence of macromolecules on chemical transport. Environ. Sci. Technol. 23, 1278-1286.
• JOHNSON W.P., and AMY G.L. (1995) Facilitated Transport and Enhanced Desorption of Polycyclic Aromatic Hydrocarbons by Natural Organic Matter in Aquifer Sediments. Environ. Sci. Technol. 29, 807-817.
• KLUTE A., and DIRKSEN C. (1986) Hydraulic conductivity and diffusivity: laboratory methods. In Methods of soil analysis (ed., SOIL SCIENCE SOCIETY OF AMERICA), Vol. 1, pp. 687-734. 677 South Segoe Road, Madison WI
• KOOL J.B., PARKER J.C., and ZELAZNY L.W. (1989) On the estimation of exchange exchange parameters from column displacement experiments. Soil Sci. Soc. At the. J. 53, 1347-1355.
• SCHWEICH D., and SARDIN M. (1981) Adsorption, partition, ion exchange and chemical reaction in batch reactors or in columns - a review. J. Hydrol. 50, 1-33.
• VAN GENUCHTEN M.TH., and PARKER J.C. (1984) Boundary conditions for displacement experiments through short laboratory soil columns. Soil Sci. Soc. At the. J. 48, 703-708.
• Zurmühl T., DURNER W., and HERRMANN R. (1991) Nonequilibrium observations during undisturbed and unsaturated soil columns. J. Contam. Hydrol. 8, 111-133.
• TOTSCHE, K.U., (1995) Inverse Parameter Determination in the Advection Dispersion Equation: Uniqueness is guaranteed ? Mitt. German. Bodenk. Society, 76: 177-180
• TOTSCHE, K.U., J. DANZER, AND I. KÖGEL-KNABNER (1997) DOM-Enhanced Retention of Polycyclic Aromatic Hydrocarbons in Soil Miscible Displacement Experiment. J. Environ. Oual.

A

storage containers

B

peristaltic pump

C

laboratory columns

D

Vacuum pump and reservoir

e, F

Flow Cells

G

fraction collector

H

AD / DA conversion and measuring control unit

L

gradient former

P1

hose

P2

Vacuum hoses

1

column inlet

2

sprinkler

3

headspace for gas sampling

4

Minitensiometer

5

sample cylinder

6

O-ring

7

Porous plate

8th

column outlet

9

bleed screw

10

separable pedestal

11

quick release

12

TDR probes

13

Sprinkler cover plate

14

Upper bleed screw

15

Sprinkler base plate

16

Glass capillaries

17

cavity for homogeneous flow the capillaries

18

O-ring seals to the sprinkler unit

19

groove for receiving the column cylinder

20

drilling for gas flow supply

21

Plinth cover ring

22

O-ring seal to the porous plate

23

cavity for the effluent

24

Plinth base plate

Claims (1)

Scalable, semi-open column device for the detection of chemical, physical and hydraulic parameters of water and mass transport in porous media, consisting of a sample cylinder ( 5 ) with side-mounted holes, the mini-tensiometer ( 4 ) and TDR probes ( 12 ), a divisible column foot ( 10 ), consisting of a cover ring ( 21 ), the lower end of the sample cylinder ( 5 ) encloses flush and watertight, a base plate ( 24 ) with a column outlet ( 8th ) and a bleed screw ( 9 ), a porous plate ( 7 ), wherein the porous plate ( 7 ) from the base plate ( 24 ) is recorded so that this the lower end of the sample cylinder ( 5 ), wherein the base plate ( 24 ) from the cover ring ( 21 ), a headspace fumigation and gas sampling room ( 3 ), the horizontal gas inlet openings ( 29 ) so as to allow fumigation and gas sampling, the headspace fumigation and gas sampling room ( 3 ) tightly with the upper end of the sample cylinder ( 5 ), a sprinkler unit ( 2 ) with a column inlet ( 1 ) and specially arranged glass capillaries ( 16 ) passing through the column inlet ( 1 ) are supplied with a percolation liquid, so that a uniform volume drop formation and a homogeneous, area-proportional irrigation can be achieved, the sprinkler unit ( 2 ) on the headspace fumigation and gas sampling room ( 3 ) can be placed tightly, several quick-release fasteners ( 11 ) for fixing sprinkler unit ( 2 ), Headspace fumigation and gas sampling room ( 3 ), Sample cylinder ( 5 ) and pedestal ( 10 ), a precolumn system for providing the percolation solution, consisting of a plurality of storage vessels (A) with transport hoses (P1) and a gradient former (L), a controllable peristaltic pump (B) and with the column inlet ( 1 ) of the sprinkler unit ( 2 ), wherein the percolation solution by the Gradientformer (L) from several solutions, the different reservoirs (A) originate, can be produced in the flow in time-variable mixing, a Nachsäulensystem with a vacuum reservoir and a vacuum pump (D) for the promotion and Filling the effluent percolation solution and an AD / DA conversion and measurement control unit (H) for data acquisition of the sensors (TDR probes ( 4 ) Tensiometers ( 12 ), Sensors in the flow cells (E, F)), for controlling the peristaltic pump (B) of the gradient former (L) of the fraction collector (G) and for controlling the vacuum pump with reservoir (D).