WO1995015487A1

WO1995015487A1 - Method and device for the analysis of water or soil

Info

Publication number: WO1995015487A1
Application number: PCT/DE1994/001433
Authority: WO
Inventors: Reinhard Niessner; Thomas Baumann; Ulrich Panne; Frank Lewitzka; Helmut Heel
Original assignee: Cosmos Messtechnik Gmbh
Priority date: 1993-12-02
Filing date: 1994-12-02
Publication date: 1995-06-08
Also published as: DE4341016C2; DE4341016A1

Abstract

The invention enables water or soil to be analysed rapidly and accurately on site for monitoring or control purposes. The presence or concentration of at least one chemical substance is determined by spectroscopic means. In the preferred embodiment, a laser pulse from a laser (3) is passed along a feed fibre (1) to a probe (A) and the fluorescence spectrum emitted in the vicinity of the probe is transmitted along a viewing fibre (2) to a detector module. Also in the preferred embodiment, an energy-normalisation signal is generated for the detector by an integrator circuit.

Description

Method and device for water and soil analysis

The present invention relates to a device for water or soil analysis, the presence or concentration of at least one substance being measured. The soil analyzes relate in particular to landfills, such as residues and / or special waste landfills, the permeability of which is intended to be monitored or analyzed for pollutants. In the general application of the invention in the field of water monitoring and soil analysis, the substances to be analyzed are in particular mineral oil products and the polycyclic aromatic hydrocarbons (PAHs) contained therein.

In principle, it is desirable to avoid harmful environmental influences in the water, such as in surface water, and in the soil, or to identify them as early as possible. In particular when sealing residues and / or hazardous waste landfills, long-term contact of the deposited substances with the environment, such as surrounding water, surrounding soil and the ambient air, is to be prevented. Particular attention is paid here to the resources used directly by humans, especially to the protection of water and / or groundwater.

However, recent examples teach that pollutants can leak into the biosphere with conventional sealing systems. The earlier this leakage - a punctual or extensive failure of the seal - or the continuous penetration of individual pollutants or groups of pollutants through the sealing system can be recognized, the more effectively and cheaply a renovation is possible.

In the event of a leak, the spread of pollutants within the aquifer must be particularly avoided. If the pollutants are only inside the aquifer, remedial measures are only time and cost intensive, apart from the fact that the biosphere suffers from the pollutants until remediation. In addition, a further spread of the pollutants that are not covered by the remediation can take place in the aquifer. These pollutants can e.g. endanger or impair the groundwater supply.

The safety of a landfill base seal is usually demonstrated on the basis of standard soil mechanical tests. These include the well-known permeability tests (DIN 18130 T 1: determination of the water permeability coefficient, Beuth, Berlin / Cologne 1989), but also the diffusion and adsorption tests, which have so far only been carried out on a laboratory scale (Göttner, J . -J. And Schnei¬ der, W.: Experimental determination and relevance of true-to-reality characteristics of mass transport through mineral seals. In: Jessberger, HL (ed.): Modern landfill technology - reports from the 2nd Bochum Deponiesemi¬ nar, 209-222 (1990); Schneider, W. and Göttner, J.-J.: Pollutant transport in mineral landfill seals and natural clay layers. Geol. Jahrb. Series C 58, 1-132 (1991); Simons, H. and Reuter, E.: Development of test methods and rules for the production of landfill seals made of clay to protect groundwater, Mitt. Inst. Grundb. Bodenmech. 18, 1-228 (1985); Finsterwalder, K. u. Mann, U.: Mass transport through mineral Abdi In: Jessberger, HL (ed.): Modern landfill technology - reports from the 2nd Bochum landfill seminar, 209-222 (1990); Klotz, D.: Laboratory tests with cohesive materials to determine the hydraulic parameters and the sorption properties of selected pollutants. Currently German geol. Ges. 141, 255-262 (1990); Mott, HV u. Weber, WJ, Jr.: Factors influencing organic contaminant diffusivities in soil-bentonite cutoff barriers. Environ. Be. Technol. 25: 1708-1715 (1991)).

Apart from the monitoring of the landfill environment in the course of the preservation of evidence - here, above all, regular examinations of the chemical quality of the groundwater are to be mentioned - regular control systems have been only recently used for municipal waste disposal sites. Controllable sealing systems in the United States have been required for hazardous waste disposal since 1985 (US EPA: Covers for Uncontrolled Hazardous Waste Sites, US EPA, Office of Emergency and Remedial Response, EPA / 540 / 2-85 / 002; Washington DC (1985)) . Also for new developments in the field of landfill technology (Düllmann, H.: Long-term behavior of landfill seals - report on the exposure of test fields on the Goldern-Pont landfill. Published by Grundbauinst. LGA Bayern 51, 27-63 (1988); Schevon, GR and Da as, G.: Using double liners in landfill design and operation. Waste Manage. Res. 4, 161-176 (1986); Finsterwalder, K. u. Legs, R.: Abdicht¬ systems from DYWIDAG mineral mixtures , Fundamentals and Experience, Published by Grundbauinst. LGA Bayern 65, 157-182 (1992)) and in the absence of a geological barrier, sealing systems with integrated control systems have been increasingly implemented in recent years.

As a rule, the control systems mentioned consist of a control drainage (gravel drainage / drainage fleece) located between natural (conventional) and artificial base seal, which collects the seepage water accumulating under the seal and feeds it to the seepage water collector, or the leakage water accumulation via leakage warning devices reports (Hodzic, A.: Planning an integrated waste recycling and disposal center (Weilheim-Schongau district): In: (Ed.): Conference documents 3rd exhibition congress Waste Management March 25-27, 1992 (1992); Hämmerle, E.: Implementation of TA waste in landfill construction. Published foundation engineering LGA Bayern 65, 253-270 (1992)). The control and monitoring systems mentioned above have in common that the detection of a penetration of pollutants by the seal takes place only after the passage of the sealing system. Other control systems are based on the measurement of the specific electrical resistance or the intrinsic potential in or below the mineral seal, which changes in the event of a leak (Dewiera L., Ledoux, E. and Marsily, G. de: Estonation and detection of leaks beneath landfills. In. Gronow, JR; Schofield, AN and Jain, RK (ed.): Land disposal of hazardous waste: Engineering and environmental issues, 69-83 (1988); Geutebrück, E .: Detection and delimitation of soil contamination using the self-potential method. Petroleum, natural gas, coal 108; 179-181 (1992)).

In the case of the legally prescribed groundwater measuring points, a noteworthy discharge of pollutants from the landfill is also necessary, since the emerging pollutants are greatly diluted in the groundwater and can therefore only be detected with difficulty despite highly sensitive analysis. The same applies generally to water and soil analyzes.

The invention is based on the object of providing a method and a device for water or soil analysis, the disadvantages mentioned above being avoided and which also enabling individual components to be analyzed on site as early and as precisely as possible.

This object is achieved with a method and a device according to the claims.

The method and the device according to the invention are preferably based on time-resolved laser-induced fluorescence spectroscopy. This procedure allows even low concentrations (down to to ng / 1) of pollutants can be determined quickly and accurately. The light for the excitation of the fluorophores is preferably generated by a pulsed laser, a modulated laser or by a laser coupled to a dye laser, whereby measurements can also be carried out at several wavelengths. The emitted laser is further preferably coupled into an optical system, preferably into optical fibers, such as a multimode quartz fiber with a step index, and directed to a sensor head. The emitted light is further preferably led via the multimode quartz fiber with a step index to a box car integrator or to an optical multi-channel analyzer and preferably to a monochromator, photomultiplier and a digital storage oscilloscope. The spectrum is recorded there preferably over time and over the wavelength, and is preferably evaluated by means of a factor analysis. The time-resolved, multidimensional fluorescence spectrum of the pore or leachate is measured when using the method according to the invention or the device according to the invention in a landfill within the landfill seal on site, with the fluorescence spectrum of the leachate at least compared to another measuring point within the landfill and used as an indicator for the transport of water and / or pollutants.

In this case, a plurality of fiber-optic sensors are preferably arranged at characteristic and / or endangered points on the landfill seal, such as, for example, low points of the seal, seams of plastic sheets in the case of combination seals or passages of pipes or shafts through the landfill seal. The sensors are further preferably placed at different depths within the landfill seal and are preferably linked by a multiplexer to form a sensor network. When using fluorescence spectroscopy, artificial, the pollutants, if necessary, in the absence of sufficient, detectable amounts of fluorescent pollutants in the leachate simulating fluorescent dyes, for example, the landfill content, such as the garbage, added or applied to this. Fluorescent dyes (eg uranine) which are chemically stable and have similar physical / chemical properties to the pollutants to be measured are preferred. Due to the similarity of the physico-chemical properties, these simulate the pollutants. The functionality, in particular of a landfill seal, can thus also be monitored with regard to non-fluorescent pollutant groups. This enables spatial and temporal monitoring of the landfill seal.

The sensor fibers are led from the landfill to an evaluation device, on which the further structure, in particular consisting of the laser and the detector module, is located. With the invention, as shown in the example of a landfill seal, surface water and soil can be monitored, checked or analyzed cost-effectively. The detection of even small amounts of contaminants e.g. when penetrating the landfill seal, it is in any case timely that sufficient time can be taken for countermeasures to remedy the failure of the seal and the contamination of the groundwater or sediments not belonging to the landfill structure can be averted.

As already mentioned, however, the invention can also be used generally for the analysis of water and / or soil, as required. The substances to be analyzed are in particular mineral oil products and the polycyclic aromatic hydrocarbons contained therein or also other substances and / or gases to be measured.

Preferably, a neural network can be used for signal processing in the evaluation by means of appropriate software for the signals received by the sensors. Such an evaluation method is described, for example, in Knorr, FJ and Harris, JM, Analytical Chemistry 1981, vol. 53, p. 272. With the aid of a large number of parameter sets in which the result (the output parameter or the output parameters) is known, the neural network is trained (the weighting factors adapted) until the desired result is obtained for each parameter set is achieved or the error becomes minimal. In a trained neural network, meaningful results are then achieved even with new input data. The raw data of, for example, 50 measuring points on the spectral axis and 500 measuring points on the time axis are recorded, resulting in a total of 25,000 measured values. Because of their quantity, the raw data of the time-resolved spectrum cannot be used as input data. This raw data matrix is therefore particularly preferably subjected to a factor analysis which breaks down the two-dimensional data set into a set (typically 3) of orthogonal vectors, spectra and decay curves. This results in a number (typically three) of spectra and associated time constants. Exponential decay curves, which are folded with the impulse response of the detection system, are assumed. As a result, the description of a decay curve is reduced to a single number, the time constants. This preferred iterative method minimizes the error square sum in order to adapt the model data matrix to the raw data matrix. The stability of the adaptation is preferably increased if the permitted range of the permitted time constants is restricted.

If the consideration of the spectra and time constants still represents an excessive amount of data for a neural network, the spectra can still be subjected to a suitable transformation (Fourier or Hadamard). This combination of data reduction and use of neural networks is considered to be flexible enough to be able to be adapted to all areas of application. This means that the starting parameters for the neural network can also be a total PAH concentration or, as in the case of the landfill, the concentration of the fluorescent markers. Another possibility is the integration of further measuring probes in the sensor system. The additional measurement of pH, electrical conductivity, oxygen content, temperature and possibly optical parameters such as light absorption and scattering are considered here. Since these parameters either directly or indirectly influence the fluorescence signal of the substances to be analyzed or of the natural fluorophores, their measurement and consideration in the evaluation by the neural network can improve the accuracy of the sensor system.

The results of the factor analysis, spectral information and time constants serve as input parameters for the preferred neural network. The output parameters depend on the planned application. For water monitoring, e.g. prefers a purely qualitative analysis, such as a simple YES / NO answer, which indicates that a limit value has been exceeded. In other cases, an indication of the quantitative pollutant concentration is preferred and / or an identification of the various substances determined, such as different types of oil. Training of the neural network with measurement data from real samples is particularly preferred.

In addition, a function and performance control can preferably be provided in which the Raman scattered light signal of the water is evaluated.

The use of laser-induced, time-resolved fluorescence spectroscopy in environmental analysis has the following advantages:

It is extremely sensitive, it works almost continuously, with the help of optical fibers it can be measured at any measuring point, even difficult to access (see basic sealing of a landfill), Relative to the total number of existing substances, the number of fluorescent compounds is low and the process is relatively selective. Interfering, also fluorescent substances can often be distinguished from the PAHs of interest due to their faster fluorescence decay behavior.

The objects, advantages and features of the invention are set forth below by way of examples and with reference to the

Drawing explained in more detail. Show it:

1 shows a preferred sensor head for the method according to the invention and the device according to the invention, which can be guided to the measuring location in a preferred guide tube shown,

2 shows a preferred construction of a laser module and a preferred device arrangement according to the invention,

3 shows a preferred detector module,

4 shows a preferred placement of sensors according to the invention in a landfill seal and

5 shows a schematic illustration of spectra measured as examples in a landfill leachate collector as a reference signal and comparison spectra measured in a pore water of the landfill seal.

The sensor head A shown in FIG. 1 preferably has an excitation fiber 1 and an observation fiber 2, both of which preferably consist of quartz and converge towards one another towards the free end of the sensor or are arranged at an angle. The angle between the excitation fiber 1 and the observation fiber 2 is particularly preferably between 10 ° -20 ° and preferably about 14 °. The laser pulse which is preferably emitted by the preferred laser module shown in FIG. 2 is conducted into the sensor head via the excitation fiber 1. The emitted fluorescence spectrum is guided to the detector module, for example according to FIG. 3, via the observation fiber 2. The sensor head A can be positioned with a guide tube B at a desired location, for example in the landfill area. The guide tube B serves to mechanically protect the sensor head A and is connected to the sensor head A before the measurement. In addition, it causes an increase in the weight, which is desirable for lowering the probe into a borehole. The sensor heads alternatively consist of one part. In particular, mechanical protection of the fibers in the sensor head is desired. Radial bores are preferably provided in the guide tube for screwing in anchoring elements.

Figure 2 shows a preferred laser module. A pulsed nitrogen laser 3 is particularly preferably provided, which particularly preferably delivers a laser beam with a wavelength λ of approximately 337 nm. A repetition rate of the nitrogen laser 3 of particularly preferably approximately 15 Hz and an average pulse energy of approximately 1 mJ are provided. The temporal half-value width of the symmetrical pulse is approximately 0.6 ns ± 0.1 ns. The laser is focused on the excitation fiber 1 using a focusing device 4, such as a quartz lens 4. A part of the primary beam is particularly preferably directed to a further quartz fiber 1 a via two beam splitters 5, 6 arranged at right angles to trigger the detector and connected to a trigger unit 7, such as a photodiode. A fiber position D is preferably adjustable. The deflected light of the first beam splitter 5 is preferably focused with a further focusing device 4a, such as a plano-convex quartz lens 4a, to form a preferably arranged pyroelectric energy measuring head 8. An integrator circuit can thus preferably provide a signal for energy normalization for the detector.

The excitation fiber 1 and the probe A arranged thereon, which is particularly preferably a fiber-optic probe A, can be moved via a preferably provided xy measurement displacement C and if necessary, provided deflection and guide devices are repositioned. The observation fiber 2 runs from the fiber optic probe A via similar devices to the detector module.

The detector module is shown in FIG. 3. The observation fiber 2 is preferably arranged on a fiber holder 9, which is more preferably connected via an x-y fiber bundle coupling 9a and a fiber bundle 11 for cross-sectional conversion to the input slit of a spectrograph 10 of the detector module. The observation fiber 2 is preferably connected directly to a circular end of the cross-sectional converter 11. The observation fiber 2 from the x-y fiber bundle coupling 9a to the input slit of the spectrograph 10 is preferably 1.50 m long. Several reflector and lens devices and a triple grating 10a are present in the spectrograph.

An optical multichannel analyzer 12 is preferably arranged in the focal plane of the spectrograph 10 and has a preferably red-sensitive photodiode array with an image intensifier. The photodiode array is further preferably provided with a "gateable" and "proximity-used" image intensifier (MCP, microchannel plate). The time resolution is preferably achieved with a high-voltage pulse that opens the MCP for preferably 5 to 6 ns. A preferred trigger signal for the high-voltage pulse is generated via an HV pulse generator, which is preferably controlled by a digital delay generator or delay generator 13. With the primary optical trigger pulse as the zero point of the relative time base, the delay generator preferably provides variable length delay times for triggering the HV pulse of the MCP relative to the laser pulse in variable step sizes. In this way, the time axis is preferably scanned sequentially. The reading process of the diode array is preferably also synchronized via the HV pulse generator and is therefore directly related to drawing to the time base generated by the delay generator. The multi-channel analyzer 12 preferably supplies a signal to an evaluating computer E which, according to its programming, evaluates the signals and delivers a qualitative and / or quantitative result.

FIG. 4 illustrates a measurement setup within a mineral landfill seal if the method according to the invention or the device according to the invention is used to monitor or control a landfill. The sensors A are installed at different depths within a mineral seal 15, preferably below a leachate line, on the edge wall and / or in the landfill area. Reference probes 16 are located in the leachate pipe. If the leachate drainage fails, an accumulation of leachate near the low points and thus accelerated transport through the base seal can be expected.

The basis of the evaluation strategy pursued is preferably the reduction of a time-resolved emission spectrum to the underlying factors, such as preferably the emission spectra and decay curves of the fluorophores involved. First of all, the dispersion of the spectrum within the fiber is preferably compensated for by means of preferably two reference spectra. In the following, the spectra along the wavelength axis are processed with a FIR filter and artifacts due to cosmic rays or incorrect discharges of the laser along the time axis are eliminated with a spike filter based on the spline interpolation. Before the actual identification and quantification, the number of components that vary independently of one another is then preferably determined using a rank analysis. With this information, the time-resolved spectrum can finally, according to the complexity and quality of the data or the requirements of the user, either by means of factor analysis or alternatively by a Rank annihilation factor analysis (RAFA) can be broken down into the characteristic spectral and temporal components of the components.

A gradual penetration of pollutants in the landfill seal is indicated by the increasing similarity of the three-dimensional spectra (wavelength x time x intensity) of the reference probe and the probes within the base seal. In this case, slight deviations in the spectra occur, which are caused by the chromatographic separation of the complex leachate into individual pollutant groups. This fact is shown in FIG. 5. A sudden failure of the landfill seal is manifested in a sudden change in the measured spectra and almost identical spectra of sensor A within the seal and the reference sensors 16.

Claims

Patent claims

1. A method, in particular for water and soil analysis, the presence or concentration of at least one substance being determined or measured, characterized by on-site measurements using spectroscopy.

2. The method according to claim 1, characterized in that a fluorescence spectroscopy is carried out, which is time-resolved and / or laser-induced.

3. The method according to claim 1 or 2, characterized gekennzeich¬ net that the fluorescence spectroscopy is carried out using a pulsed laser or a laser coupled with a dye laser.

4. The method according to claim 1, 2 or 3, characterized by generating the light for the excitation of the fluorophore by the laser and coupling the light through the optical fibers to a sensor head located at the measuring location.

5. The method according to any one of the preceding claims, marked by recording the emitted light as a spectrum over time and over the fluorescence intensity and evaluation by means of factor analysis.

6. The method according to claim 5, characterized by interpreting the data obtained by the factor analysis by means of a neural network.

7. The method according to any one of the preceding claims, marked by comparing a time-resolved, multi-dimensional fluorescence spectrum, which was recorded on site, with a reference spectrum.

8. The method according to any one of the preceding claims, marked by applying at least one suitable fluorescent marking substance to the medium to be measured.

9. Use of a method according to one of the preceding claims for controlling a landfill.

10. Analysis device, in particular for carrying out a method according to claims 1 to 8, wherein the presence or the concentration of at least one substance is measured with a laser (3), an excitation fiber (1), a probe arranged at the measuring location ( A) and a detector device, wherein a laser beam is guided from the laser (3) to the probe via an excitation fiber (1) and the spectrum emitted at the measuring location is guided to the detector device via an observation fiber (2).

11. The device according to claim 10, characterized by a trigger device (7) for triggering the detector device, wherein part of the laser beam emitted by the laser is guided to the trigger device (7) via a beam splitter device (5, 6).

12. The apparatus of claim 10 or 11, characterized gekenn¬ characterized in that a part of the laser beam emitted by the laser (3) is guided to a pyroelectric energy measuring head (8) by a beam splitter device (5) which has a signal for energy normalization for the Detek¬ provides gate equipment.