New technology continuously monitors landfill seepage

German researchers have just developed a new infrared spectrometer to detect contaminated water, using a new technology called evanescence field analysis (EFA). This new method appears to combine the advantages of traditional alternative methods of water sampling, whilst avoiding some of the drawbacks.

The new technique has been developed at the Fraunhofer Institute for Physical Measurement Techniques (IPM). Whereas traditional methods of sampling surface and groundwater from around landfill or chemical plants consist of regular water sampling at different depths and times followed by laboratory analysis, EFA continuously monitors seepage and provides more immediate results, possibly lowering costs of clean-up.

However, in the past, infrared methods of detecting contaminants in water poses a particular problem, as the water absorbs too much infrared radiation in the wavelength of interest.

Dr Annette Braun from IPM explained, “The key element of our new spectrometer is an infrared-transparent silver halide fibre through which the measuring beam is conducted. As in fibre-optic cables, its inner surface is completely reflective. If contaminants in the surrounding leachate contact the outer surface of the fibre, changes are introduced to the electrical field. This evanescent field, in turn, causes variations in the infrared radiation which are analysed by the detector.”

This fibre is able to separate water and contaminant because it is coated with a hydrophobic polymer. The contaminants, usually aromatic and aliphatic hydrocarbons, penetrate this mantle, but water does not. At one end of the rod-shaped instrument is a watertight infrared source. The fibre, exposed to the surrounding water, is connected to the detector at the other end of the device.

The rod-shaped measuring instrument is entirely submerged into a borehole and the measurements can be read on a computer. According to IPM, the invention is causing quite a stir and plans are being made for serious production of the new spectrometer. The team is also looking into further miniaturising the device.

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