A methanogenic microbial community immobilised on an inert carrier was acclimated to a mixture of chlorinated aliphatic hydrocarbons in a bioreactor used for their detoxification. The mixture contained trichloroethylene (TCE), tetrachloroethylene (PCE), carbon tetrachloride (CT) and hexachlorobutadiene (HCB). An attenuated total reflection-Fourier transform infrared (ATR-FTIR) optical sensor was developed for continuous on-line measurements of the toxic compounds in the dechlorinating bioreactor. The sensor consisted of an ATR internal reflection element (IRE) coated with an extracting polymer which was continuously enriched with the toxic compounds. The bioprocess was monitored through the sensor, which was coupled permanently to the bioreactor, over a period of three days of continuous operation. The sensor tracked the progression of absorbance spectra over time in a non-invasive manner. The concentration of organochlorine compounds in the bioreactor was predicted from the absorbance spectra using a partial least squares (PLS) calibration model which was developed for all components simultaneously. The accuracy and reproducibility of this ATR-FTIR sensor was tested by checking the spectra-based concentration values of the toxic analytes in the bioreactor effluents against off-line gas chromatography (GC) measurements. This novel sensor is useful for routine continuous on-line monitoring of the dechlorinating bioreactor.

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