Monitoring of pollutant in waste water by infrared spectroscopy using chalcogenide glass optical fibers

Abstract

Infrared optical fibers based on chalcogenide glass are used as sensor for the determination of volatile organic pollutants in groundwater. The system work following the fiber evanescent wave spectroscopy principle, so-called fiber evanescent wave spectroscopy (FEWS). It was tested in situ, in real time, under real-world conditions. The measurement set-up consisted of a FTIR spectrometer (BRUKER V22), coupled with the fiber (about 2m), and a cooled mercury–cadmium–telluride detector. A special kit provided by Bruker was connected on the spectrometer to focus the infrared beam from the black body at the entry of the fiber. Some preliminary pilot scale tests, led in an artificial aquifer, show that the fiber permits access to the absorption line positions in a wide range from 4000 to 800cm−1. Moreover, it is shown that the original design of the fiber enables detection of weak concentrations of pollutants down to 1ppm of C2Cl4. Then the experiments in “real-world” conditions are carried out after having applied a proper protection on the fibers. A comparison with the chemical analysis data shows that the optical fibers enable to follow the evolution of pollutant rates in water versus time. Finally, this work is promising in view of installing some permanent checking devices into wells to control the rate of pollutants in groundwater of landfill.